Explaining the Mystery of Subaru Radiator Caps

[@NateTeunissen]

Dude, you guys just saved me. Was having an issue with my overflow filling to the brim with coolant, and my car then overheating. Everything I was reading was saying head gasket. I watched this video just on a whim, and it made me realize, I actually had my caps swapped. Yall are the best.

[@FlatironsTuning]

Very glad to hear that this helped you. Stay Tuned!

[@NateTeunissen]

@@FlatironsTuning Wound up being the head gasket anyway *super excited*. But I still learned a ton from these videos

[@FlatironsTuning]

@@NateTeunissen Sorry to hear that, but it definitely is critical to have those caps in the correct locations. Hopefully that will help keep your engine cool going forward. Thanks!

[@TheRandomname951]

@@NateTeunissen can I ask what year your Subaru is/was? Thank you!

[@TheRandomname951]

@@FlatironsTuning do you know if this hold true for the CSF radiator as well?

[@colonelredracing]

Hi Jon, I hope this solves your cooling problem and thanks for the plug. My solution on our sprint/endurance cars is to simply use the stock/oem caps as Subaru intended, no aftermarket caps to fiddle around with. If you don't get the caps right you can spend a ginormous amount of time and effort trying fix an overheating issue. Putting the caps on correctly may not solve the overheating, it could be something else, but you have to eliminate that variable first. Next, what we've found is most important is proper ducting into the radiator and sealing it all around the edges so the airflow cannot slip past it. A vented hood makes a big difference too. If you watched our KZbin video on the last Cascade Enduro you heard me say that after 6 hours of racing our coolant temps were still slightly below normal on the OEM gauge. Later our datalogger confirmed our temps. And for your audience, the rule of thumb so you don't get the caps swapped backwards: The cap with "ears" goes on the expansion tank because Subaru wants you to open that one to fill/check the coolant. The round cap without ears goes on the radiator because Subaru doesn't want you to take it off, so they make it harder to grip it.

[@FlatironsTuning]

Thanks very much for pointing us in this direction. It has been enlightening to say the least! Stay Tuned!

[@89autoworks]

Thank god. This just saved my ass on the side of the road.

[@FlatironsTuning]

@@89autoworks Oh man. Glad you found the video and that it helped. Stay Tuned!

[@89autoworks]

@@FlatironsTuning I can’t wait till my car is done, would love to take a road trip out to your guys place!

[@89autoworks]

@@FlatironsTuning yeah and I lied, car is still over heating…. No bueno.

[@ozzysgarage]

I've ran Mishimoto radiators on a few cars now and I must say that using OEM caps are the way to go. I always had overheating issues when running anything aftermarket. Go OEM and in the proper location, you'll be good to go!

[@FlatironsTuning]

Totally agree. Thanks for watching and Stay Tuned!

[@jessem9832]

whats the correct way the caps go? I want to buy oem for both

[@ozzysgarage]

@@jessem9832 the perfect circle one is the radiator, the one with the lil side tabs is the expansion tank. Hope that makes sense

[@SCOOBTUBE]

The Subaru cooling system can be a right pain at times if you don't know the difference between the expansion cap and the radiator cap, however it's made worse by companies listing all the caps as rad caps.. 1 way valve on the radiator, 2 way on the header.. Very Interesting video for people with coolant issues being led to believe it's hg failure 👍

[@FlatironsTuning]

Thanks for the comment and thanks for watching. Stay Tuned!

[@PeterHernandez-lg2eh]

More stuff to worry about with the Subaru

[@5501pickopicko]

Great video as always guys 👌 I’ve tried to explain this so many times to friends in the Subaru community but now you’ve done the perfect video explaining it all, I can share the link with them. Another pointer not covered is the reduction in size of the overflow tank usually when fitting front mount intercoolers, this can cause issues whereby the coolant overflows the overflow tanks capacity and then when the two way cap draws back when cooling down, it empties the smaller capacity overflow tank and draws air which then causes the air pockets in the system and head gasket failure. Keep up the great vids guys 🤘

[@FlatironsTuning]

Thanks very much Sam, and great point about the expansion tank. That is definitely another gotcha for sure. Thanks for watching and Stay Tuned!

[@stevemartegani]

I've seen a lot of folks ditch the expansion tank for track use. My car, which is basically one giant experiment, is actually running an N/A radiator + JDM crossover pipe without the expansion tank and only one radiator fan with the USDM EJ205. Coolant temps have stayed below 200 on the track so far. Ill find out how it does with the new turbo tomorrow :)

[@FlatironsTuning]

Thanks for the comment. I think that the expansion tank is actually they key to the solution, not the problem. Thanks for watching and Stay Tuned!

[@tommyvercetti6035]

I'm surprised you guys didn't already know this. I have been trying to tell people this for years!

[@FlatironsTuning]

All to easy to overlook the fine details. Had to do what we could to get the word out. Thanks for watching and Stay Tuned!

[@jeremiahjorenby2275]

The reason for the expansion tank is that due to the location of the turbo charger on dual cap cars, the cap on the radiator is no longer at the highest point of the system. In order for the system to function properly, the fill point must be at the highest point in the system (just like how a brake bleeder must be at the top of a caliper). Notice how the 2010-2012 Legacy GT did not have an expansion tank because it has a bottom mount turbo.

[@FlatironsTuning]

Thanks for the comment. Stay Tuned!

[@Edward-bz5jh]

I love that explanation!

[@PeterHernandez-lg2eh]

This makes sense. Guess I messed up. I burped air on my koyorad radiator side no bueno

[@barryegan1138]

Hi guys , great video , I do a lot of track work in my Impreza and I’m a plumber by trade so My understanding of the way the caps work is that both caps lift sending expanding coolant in to the expansion tank (at different pressures) but only the header tank cap draws the coolant back as that is the highest point of the system. If you ever noticed when the engine is cold , say it was left over night the coolant level is never right to top and there is an air gap and once the system pressurises again this air gets pushed out and the cycle of push/pull continues. If you have the 2 way cap on the radiator you may get air pockets forming and this is a lower point in the system hence the overheating. I could be wrong but it is may understanding of it. A friend with a s204 had this happen at the Nürburgring and a head gasket failure shortly afterwards. Caps were fitted incorrectly.

[@FlatironsTuning]

Thanks for the comment Barry, and that is our understanding about the issue with the 2-way caps as well. Thanks for watching and Stay Tuned!

[@tysonheller1612]

So happy to actually see or find a very concise video about this topic as I and apparently many many others had absolutely no clue about this one way & two way valved cap my OEM radiator on my 2012 WRX finally let go at the crimped plastic endtanks and started leaking. Swapped out for a koyo rad radiator and radiator hoses so it obviously came with their cap and upon install was when I started to find out about all this one way two-way valve craziness and obviously when I started searching online trying to find out why and where to put the higher pressure cap where to put the two-way valve and if it was even worth using one of the higher rated pressure caps. I most definitely did see very erratic coolant temps and it would get over 208 and rather quickly once I understood what was going on and had the correct pressure caps in the right locations everything's calmed down and worked out wonderfully and when I pull my car in the garage and shut it off you can actually hear that vacuum and you can hear the system sucking the coolant back out of the overflow which kind of tripped me out at first until I realized what was going on and that that was actually correct but thank you very much for the content in this video it was wonderful also very excited to hear what else you find out with continued testing on this topic.

[@FlatironsTuning]

Thanks very much for the comment. Stay Tuned!

[@atlasintegrations4114]

Excellent video. That is a real problem solving topic. I run a 2002 WRX in Arizona and it gets hot here. The stock configuration has done fine with +115° temps, but you cannot run the car hard during these times, obviously. Once you figure it out, I would love to improve my cooling system anyway possible. Videos like this are gold nuggets for us weekend warrior car builders. Thanks. 😉

[@FlatironsTuning]

Awesome comment! Thanks for watching and Stay Tuned!

[@micahgunnell]

Very interesting! Never would have considered this as such an important thing!

[@FlatironsTuning]

Thanks for watching and glad that the video was helpful. Stay Tuned!

[@micahgunnell]

@@FlatironsTuning Will do! I recently subbed and I’m really enjoying your content 👍😊

[@MrBillDaBear]

I’ve ran dual 2-way caps for a couple years of track days now. 1.3 bar ARC cap on the expansion tank and 1.4 bar CSF cap on my radiator. I think the important part is to have a 2-way cap on the expansion tank, and the pressure relief on the expansion tank be less than or equal the cap on the radiator

[@DJ_Driven]

If you keep the factory expansion tank it sounds like the 2-way cap should be less pressure than the radiator cap. As long as one of those two caps maintain correct pressures it looks like you're set up is safe, but if it was me I would run the factory cap on the radiator.

[@Judgedredd18]

I’m about to do the same 1.3 greddy on expansion tank and 1.4 Csf.. the oem radiator cap doesn’t fit the Csf kinda loose and leaks a little.

[@CLNracing]

On track, with the stock configuration, I had an issue with pushing tons of coolant into the coolant overflow until the lower fluid capacity caused over heating. As a quick leap of faith, at my next event I replaced both caps with 2-bar 2-way caps and never had any overheating issues, nor over filling of the overflow tank. I was not aware of the Rad cap being a 1-way cap but it makes sense why my overflow was constantly overflowing and thus overheating. I will definitely be taking a handful of caps to my next event now that I know this, but the 2-bar 2-way cap combo I have currently seems to be working.. (Aftermarket Aluminum Rad and hoses handled the higher pressure just fine.)

[@FlatironsTuning]

Glad you found a solution that works for you. I would recommend keeping a 1 way cap on the radiator, or in a pinch, having a slightly lower pressure cap on the expansion tank. But again, if you have found something that works, by all means stick with it. Thanks for watching and Stay Tuned!

[@ninjaknight-jn9ky]

Usually the radiator is the highest point, but because you have to cool the turbo and keep oil circulating you so you don't bake it if it put away hot. The turbo runs directly into the cap and as the water expands and heats it rises gets pushed out and cooler water from the engine is pulled in the expansion cap is there so that water can be forced in and out by the highest point and. And it's there directly to cool the turbo goes engine > turbo > expansion tank > radiator or overflow tank > engine , but you always want hot to be at the top of the system so that if it evaporates it likely out of the system atleast that's how I understand it. It basically a turbo timer but automatic and fully mechanical it's also nice because it forces the whole system to equalize to the radiator tank temperature also forgot about the forth hose that directly cycle just teh engine which is also the primary pumping method with the car on to cool the turbo by forcing coolant from the cooled side of the radiator into the water pump and engine and hot side of radiator I haven't rebuild a ej205 in a while it kindof faded, but that what I remember. My koyo didn't come with a cap also they're better than mishimoto. By a long shot. Aleast in terms of build quality.

[@aersoul]

I did read when I got my mishimoto radiator to installed their cap in place of the expansion tank and move the expansion tank cap to the radiator location. Besides the paperwork mentioning a 2 way cap I didn't look further to find the differences. I ended up not using the mishimoto radiator due to fitment issues (GM6 with GD7 swap) and I was just looking to replace both caps with new oem caps. I ended up with 2 high pressure caps that are shaped differently and thats when the concern arose. I was like "which cap do I need, is the 137kPa for STI and the 108kPa for WRX?" So I did digging and couldn't find anything concrete. Finally read through the service manual and it just explained which one goes where. I've yet to install the lower pressure cap on the expansion tank since I didn't see any cooling issues, but the swap is weeks old and only a couple hundred east break in miles on it. But I hace noticed my upper radiator hose pulls a vacuum after the engine is turned off and the hose collapses which caused the hose to rub on a pulley so I will install the 108Kpa on the expansion tank and see if that cures that small issue. Considering I built the car to go on track its good to see this information sooner than later. While we have our questions on our own builds, just goes to show how a team of engineers at subaru cobbled this solution and it works perfectly so long as the cooling system is being serviced per their procedures. Goes to show sometimes OEM is just fine in some applications.

[@FlatironsTuning]

Thanks for the comment Javier. Definitely take a look at your caps. If you are pulling a vacuum in the radiator hose such that it is collapsing, there is definitely an issue there. I think that getting the caps sorted should fix that issue though. Thanks for watching and Stay Tuned!

[@M3NS0]

What an huge amount of info... And what about the non-turbo subarus, with only one cap in the radiator and the expansion tank next to the radiator, with an standard plastic yellow cap? This cap on the radiator is a two way one?

[@FlatironsTuning]

Thanks for your question. The non-turbo Subaru's only have a single cap on the radiator, and that is a 2-way cap. The tank next to the radiator is the overflow, and it doesn't have a pressure cap on it, and you actually wouldn't want to seal that off. Glad that the video was helpful and thanks for watching. Stay Tuned!

[@gar24407]

This bit my ass badly. I finally communicate with Mishimoto radiator they told me the same thing. I ended up just running 2 oem caps and no issues. This should be a large red warning on the cap when they ship it. Not a foot note on paperwork nobody reads.

[@FlatironsTuning]

I definitely think that it would be better if this instruction was more visible for sure. Glad you got your issue resolved. Thanks for watching and Stay Tuned!

[@Silent_Keith]

So it wasn't the head gaskets, didn't someone say it wasn't?...😀 I'm just glad you got it figured out.

[@FlatironsTuning]

Right? I feel like we are getting to the heart of the issue, and our cooling system will be the better for it. This is why you always have to do your diagnosis work, and develop a solution based on what you find. Thanks for your help, and for being a great sounding board for this Keith. Much appreciated. Stay Tuned!

[@Silent_Keith]

@@FlatironsTuning Meh I'm always learning like anyone else. I really would have like to have seen that car go around COTA, but sometimes the cards you're dealt are just not the winner combination.

[@FlatironsTuning]

@@Silent_Keith Honestly, if this lets us figure out the cooling system and improve it (which I think it all ready has), then this may be the best thing that has ever happened to that car short of getting the dry sump figured out. Next year will be better. ;-)

[@weduhpeople8504]

@@FlatironsTuning Why not just add an Accusump?

[@Zcypot]

I have been having this issue ever since my power bump. Going to check this out when I get the car back

[@FlatironsTuning]

Hope that it helps. Thanks for watching and Stay Tuned!

[@terryloweh]

love your channel but its in dire needs of some better audio equipment but overall amazing stuff! thanks for sharing all this info

[@Yknotvideos]

The expansion tank vents to the coolant reservoir via a tube that is kept in coolant at all times. This allows the system to heat up and cool down, while pushing coolant in and out of the expansion tank without sucking air back in (which could lose your bleed of the system). Since the radiator vents to the top of the expansion tank, you want it to be able to push coolant out, but not pull anything back, because it could pull air back in and lose the bleed. The recommended way to set this system up basically allows for the proper regulation of pressure and control of thermal expansion in the system while having an ambient-pressure coolant reservoir available to the user and not allowing any air to enter the system. That being said, if you REALLY fill the expansion tank up, you probably won't ever get enough air in the cooling system to cause a problem, but if you 1. don't get the tank completely full, or 2. allow air to enter the expansion tank in some way (e.g. low coolant in the reservoir), you could end up in trouble.

[@alfredojarillo3146]

Awesome video. Here’s my experience and two cents. A few weeks ago I pulled the engine(04 EJ205) had the original aluminum expansion tank, the filler neck had a small rip due to all this pressure. Ended up changing to the plastic OEM expansion tank, but did not replace the caps. Anyways, my dad helped a bit, during the process of adding the oem super coolant(Have a 2007 2.5i A/T sitting on the side) Did notice the shape where different(didn’t give too much thought)and did not check the kPa. A few moments later my dad brought this up even though he’s never worked on an EJ. And mentioned to check the pressure readings on top of the caps, without even looking at them. Once I did.. for radiator it’s 108 kPa and expansion tank 137 kPa. Looked it up on forums and saw the difference. No overheating or anything. Mean while I still kept inspecting hoses and caps. I’d remove the expansion tank cap and see build up from I guess the old coolant. I clean it up with a toothbrush and remove the gunk. Radiator cap not a whole lot. You explaining how these caps work, specially the expansion tank cap, gave me an answer to my question tonight. Earlier today(9/23/22) took a drive from chicago to Wisconsin dells(non stop). Just check my engine bay and saw the upper radiator hose kind of swollen, pressure wasn’t released from the expansion tank cap(since I didn’t clean it before hand). I’m gonna get a cheap toothbrush and clean it. Until I get new OEM caps. This video helped me understand how these caps work, so thanks for that!

[@FlatironsTuning]

That is fantastic to hear, and glad it helped. Thanks for watching and Stay Tuned!

[@j.bow87]

This is an interesting thing of 2-way and 1-way radiator caps. When I owned my 1999 Legacy B4, it was an OE twin turbo EJ20 set up and only had the overflow tank next to the intake manifold and no cap on the radiator. I was plagued with over heating issues and thought it was a head gasket issue. After replacing head gaskets and rebuilding, could never get it to properly work right (coolant overheating). Would always overheat at idle (like an air pocket after cold start), burp it, it would be fine. Could never figure it out. I now wonder if I had a wrong radiator cap. Of course, I’ll never know as I scrapped it already 😢. But thank you for some insight and sharing!

[@FlatironsTuning]

Thanks for watching and glad that the video was helpful. If you had a 1-way cap only, most likely you would have seen radiator hoses collapse because the cap wasn't letting coolant back in, and it would go into a deeper vacuum. Most likely those other signs would have prompted further investigation. Hope that helps and Stay Tuned!

[@ricardoshi839]

I hope I can provide a bit of insight to the reasoning between pressures and locations. The radiator located cap is a one way valve so should an over pressure condition occur pressure will be released. It is a one way valve because that is not the highest point in the cooling system. The cap located on the expansion tank should be a marginally lower pressure release as you want that cap to be the main point of coolant expansion overflow. Being the highest point in the system, it will aid in burping the system. You also want this to be the place where the two way valve allows coolant to be sucked back up through to refill the cooling system from the highest point.

[@FlatironsTuning]

Thanks for the great comment. Stay Tuned!

[@mrbaldwin8819]

I've ran two after market caps for 5 years now with zero issues with heat . Ones a Cobb cap for expansion tank made by aluminate and an apex cap on mishimoto rad . The combo works for daily tuned car , I feel stumped as you guys since many have told me not to do this but seems just fine

[@FlatironsTuning]

Thanks for the comment Mitchel. There is definitely a lot to this, and the issues from the incorrect/mismatched caps would present more slowly or be less of an overall issue on a street/daily driven car compared to a race car. Thanks for watching and Stay Tuned!

[@mrbaldwin8819]

@FlatironsTuning no doubt on thar point between daily and race car set ups . I've always wondered the issues with it and also one thing I could never get answered was that some of these caps internals or valves spin freely and others are very fixed with no play . I bring this up since I wrecked a koyo cap in summit County where I was over heating and the cap had loose center and the label was soaked . Not sure if that explains the issues clear enough but thought I'd mention it

[@FlatironsTuning]

@@mrbaldwin8819 I have seen failed caps leak coolant up to the sticker/label on the cap. It seems like that is one of the ways that the cap can fail.

[@mrbaldwin8819]

@FlatironsTuning I'll Luke to see what info comes of your study that way I can finally know myself lol the failed cap thing has me confused due to the fact that Cobbs caps come Luke my failed koyo cap but I've never had heat issues but sticker is weird from heat more than anything .

[@mikestreet4339]

I'm not claiming to be an expert, but I'd like to offer my anecdotal 2-cents, in case it is useful as a datapoint for anyone researching this subject: I have been running a Mishimoto radiator on my 2011 WRX for roughly 3 years now. For the radiator itself, I purchased and installed an OEM STi 1.3 bar radiator cap, which has a slightly higher pressure rating than the stock WRX's cap IIR, and still retains the 1-way valve construction. On the expansion tank (or what I sometimes call the turbo reservoir, higher up on the engine), I placed the aftermarket 1.3 bar Mishimoto cap there. So there is no pressure differential between the two caps, and the higher cap in the system is a 2-way Mishi valve. I also installed Samco's silicon ancillary coolant hoses at the same time as the radiator. 90 degree summers, highway/stop-and-go traffic, occasional performance driving (not extended track use though), and I've had zero issues. The overflow tank will fill up when hot, and drain back into the engine upon cooling. Will be watching closely when I start HPDE courses within the year.

[@FlatironsTuning]

Glad to hear your setup is working all right so far. I'd definitely recommend dropping the expansion cap down to a 1.1 bar cap if you can. Thanks for watching and Stay Tuned!

[@HeidiFegles]

IV had really good luck with my 1.3 bar 2 way radiator cap, I have one radiator cap and seams that moving the expansion tank to the high point mine is right behind the intercooler, and in an 85 rx turbo the spare tire cubby works perfect to mount the catch can and expansion tank and set tools on when your working on it.

[@FlatironsTuning]

Nice! Very cool that you are keeping the RX on the road. Stay Tuned!

[@HeidiFegles]

@@FlatironsTuning hopefully I can keep it going and modify to keep it on the road. No point in buying new, for me the thrill is making my old car compatible with all new parts, low insurance, no attention every time I park it and get out, unless it’s a Subaru finatic that’s in the know, it’s got a special place in my heart probably the same feeling you get driving the yellow bug eye wagon. It’s such an amazing car why would you ever need a new one. Especially when you can attatch any Subaru part your heart desires at any time basically to make it handle or take what you throw at it. And the fact that at any rally the possibility of a fan having a Subaru parts store at their house is a good chance. Like my scrap bin is full of axles, hubs, struts, wheel bearings, trans parts. Motor parts. Probably extra 3 of every sensor collected over the years. And I already hauled away 20 destroyed motors to the scrap yard to then take that money and buy more Subaru parts haha.

[@Segar1991]

Hey guys, great video! So im currently having an issues with my coolant system for my 2013 wrx. I got a new radiator, radiator hoses, expansion tank and overflow tank. My radiator was oem that i purchased and it was without the oem cap. The expansion tank came with a mishimoto cap and i just put it aside and ordered 2brand new expansion/ radiator caps. After some new coolant and full burp of all air bubbles(properly done through the expansion tank) and is ready to go. I also order new thermostat, thermostat housing, and sensor. With nearly everything brand new, why am i still having problems with my overflow tank filling up and spewing out. When the car cools i never see that the coolant pulles back into the radiator. Ive done pressure tests and the head gasket is fairly new. Im completely lost by this? Is this setup not brand new?! Also my radiator fans are turning on and my car stays within 197-178range. Drove it around for an hr keeping tabs on the temps. Any ideas please help?

[@keithspence85]

Thanks again for all the information and answering all my build questions a few weeks ago. Another thank you for this very important information because after watching this and putting the knowledge to an issue I'm having in my semi I think you may have indirectly solved my issue there as well 😃 although it's not an overheating issue.

[@FlatironsTuning]

Very cool Keith, glad we could help! Thanks for watching and Stay Tuned!

[@toplistcrew7645]

I had this issue happen to me. I have a Mishimoto radiator and the cap. I bought the vehicle with it set up like this. I noticed coolant on the top of the radiator and went and bought a basic radiator cap and never had an issue again.

[@weduhpeople8504]

On my 04 sti I used to own it had a cap on the actual radiator and on the expansion tank reservoir. Ive had installed the larger Koyo radiator when I did one of my 4 engine builds and that radiator expanded from pressure in the cooling system and if I can recall had a head gasket failure. Probably due to not having a dual valved radiator cap on the expansion tank. Fast forward today now I own a 2018 Civic Type R which has an expansion tank and the radiator is cap-less. It is well known that these cars overheat on the track. I’ve done several cooling enhancement mods as well as a fully built motor and big turbo upgrade. Since then it hasn’t over heated. I think mainly from running a bigger turbo. I think maxing out the stock smaller turbo which caused more back pressure making it into a heat pump. The larger turbo has less back pressure so it’s not producing as much heat.

[@FlatironsTuning]

Thanks for the comment. Stay Tuned!

[@911CARRILLO]

Appreciate the info thank you..I was looking for aftermarket caps and could not decide which to get..I'm glad I went oem for this time around.. cheers

[@FlatironsTuning]

Excellent! Thanks for watching and Stay Tuned!

[@cmb350]

I'm definitely curious of your findings with the testing. I'll be looking for future videos. I run a Mishimoto radiator with the Mishimoto cap on the expansion tank. I think the OEM expansion tank cap is on the Mishimoto radiator. My car gets warm on track, but does not overheat. However, I have to run the heat when the ambient air temp gets over 85* otherwise it gets too hot.

[@FlatironsTuning]

Thanks for the comment, and another video is in the works. Make sure you are running the OEM 1-way cap on the radiator. If you have the expansion tank cap on the radiator, which is a lower pressure than the Mishimoto, that could cause issues. Thanks for watching and Stay Tuned!

[@PeterHernandez-lg2eh]

Does this apply to the koyorad radiator also ?

[@Martegiani]

So I just bought a Koyo Radiator and a koyo cap, the SK-C13 and it’s a two way cap. I thought the expansion tank got the two way cap and a one way cap for the radiator? Your webpage says the regular cap doesn’t fit the Koyo radiator, they look the same to me though. Should I try to fit a regular one way cap? Looks like I should return the Koyo cap. Well I’m off to watch the video of why you all got rid of your radiator cap now. Cheers

[@FlatironsTuning]

Thanks for your question. Yes, you can put the factory 1-way cap on the Koyo radiator. Thanks for watching and Stay Tuned!

[@shaneil7901]

Always learn something new from watching your videos, awesome work guys, I have an early WRX with no cap on the radiator, just an expansion tank with a cap, have I understood you correctly in that the expansion cap should be a two way valve?

[@FlatironsTuning]

Thanks for the question Shaneil. That is correct. You need a 2-way cap on the expansion tank. We actually go into detail about your specific setup in this video here: kzbin.info/www/bejne/iIi9hpd-h62em6s Thanks for watching and Stay Tuned!

[@rarevidz]

Well im running an Aftermarket Aluminium radiator with no Cap provision at all and just a cap on the Expansion Tank ,should I be running a Two Way Valve Cap????

[@FlatironsTuning]

Thanks for the question. Yes, if you only have one cap on the system, you need a 2-way cap. Thanks for watching and Stay Tuned!

[@Owensti]

Well that explains why my ej257 always has an air pocket in the expansion tank every 2-3 days. I top off my coolant every other day and can’t figure out where it goes. I have no leaks and my outfront v3 block only has 30k on the build so no way it’s the head gaskets lol, I have the mishimoto rad cap on the rad not on the expansion tank. I’ll switch them out and see what happens. My car idles fine at 181-185 but when I’m driving it doesn’t ever go below 190 and sometimes gets to 210. Never goes past that. I’ll order new caps and hopefully that solves my issue.

[@FlatironsTuning]

Thanks for watching and definitely hope this helps. Stay Tuned!

[@CHASEtheDRIVE.]

So which radiator would you suggest for longevity and cooling of the car for daily and lite track use?

[@meblake7359]

It doesn't make sense to put the 2-way radiator cap on the expansion tank and the one-way cap on the radiator because when the cooling system cools down, it contracts and there is no pulling of the coolant from the expansion tank due to the missing 2nd valve for vacuum. If the radiator has the 2 way cap and the expansion tank (which is only a reservoir) has the one way cap, coolant can be pulled back into the cooling system via the 2 way valve on the radiator. Vacuum pulls the 2 way valve open pulling coolant from the reservoir into the radiator.

[@poudrecanyonbiker]

I have an 05 LGT, does this or how does this apply to the KoyoRad Racing radiator? Didn't see any notes for this product.

[@FlatironsTuning]

Thanks for your question. It would be the exact same situation with the radiator cap as the Mishimoto because Koyo's caps are also 2-way. Thanks for watching and Stay Tuned!

[@MarioFlopsy]

thanks, just installed aftermarket radiator directly for WRX. Of course the cap which came with the radiator is two valve and without this video I will run it without knowing it. I will keep stock ones then

[@FlatironsTuning]

Glad the video helped and thanks for watching. Stay Tuned!

[@jhoelt2922]

Question! Is the expansion tank a factor when doing coolant flushes/replacement? Or only do burping from radiator like all other cars with no expansion tank..?

[@FlatironsTuning]

Thanks for watching and thanks for the question. Yes, since the expansion tank is integral to the cooling system, you would need to work with it for any task related to the cooling system. Stay Tuned!

[@jhoelt2922]

@@FlatironsTuning thanks! I asked because I found it a bit odd that my 09 Legacy 3.0r has a coolant expansion tank by the manifold like the turbo Imprezas/Leggies

[@tyree9055]

I'm running a Stage 2, 2002 WRX with a Mishimoto replacement (oversized racing) radiator with their valve on the radiator and Subaru's OEM one on the expansion tank and I have no overheating issues with my coolant (only the oil gets hot when sitting in rush hour style traffic). I don't really see the point in swapping them, but am curious to know more and as to why they did have an overheating issue?

[@FlatironsTuning]

Thanks for your question. As long as you have the staggered caps, 1.1 bar on the expansion tank, and 1.3 bar on the radiator, that should minimize any potential issues. Thanks for watching and Stay Tuned!

[@impulseproman]

wow that's a good video on overheating issue subaru

[@FlatironsTuning]

Glad it helped! Thanks for watching and Stay Tuned!

[@abelsgarage]

I have literally been dealing with this for a year now trying to figure out why I can’t keep temps down

[@Lucas-nz8em]

Such a simple concept is making my head hurt. Crazy how many years I’ve been messing around with these cars and have never encountered this issue. NOTE TO SELF: don’t swap caps. Thanks guys!

[@FlatironsTuning]

Thanks for the comment, and totally agree. It makes sense after looking into it, but it is hard to believe how many years we just put caps on the engine and never really thought about it. Glad that the video helped and Stay Tuned!

[@svensluyter2773]

Does this 2 cap solution also apply to the Subaru Outback...?

[@FlatironsTuning]

Thanks for your question. If your car has 2 radiator caps from the factory (so an Outback Turbo) then this does apply just the same. If you have a naturally aspirated engine, most likely you only have 1 cap from the factory, so you would not need to do anything to add a second cap. Hope that helps and Stay Tuned!

[@bbehzadi413]

Running CSF 1.4 cap on the radiator and HKS 1.1 on expansion tank no issues so far but hopefully you guys will come out with a better looking one way cap

[@wbernal92]

So I am running a Mishimoto expansion tank and a Mishimoto radiator. And as you know they both come with the Mishimoto caps and I was running both but I noticed my car would over heat if idled for too long. Winter wouldn't really happen much. So I'm sure this is my issue, what should I do for caps? Should I buy an oem "expansion tank cap" and put it in the Mishimoto radiator? Will it fit?

[@FlatironsTuning]

Thanks for your question. I'd recommend using the factory cap on the radiator because it is a 1-way valve, and see if that resolves your issue. www.flatironstuning.com/subaru-oem-radiator-cap Hope that helps and Stay Tuned!

[@E85_STI]

So my caps have been fine but I just did a coolant flush on my 18 STI Two days ago but the coolant was only 3,000 miles old but I’m diagnosing something but anyway my coolant hoses are collapsing under vacuum once it cools off. So I’m curious if I could clean the cap on the radiator because I had that oily residue that I messaged you guys about the other day. Crazy thing is I don’t see the oil coming in but right now I’m trying to figure out the hose issue. I also notice the coolant level will lower just a little but it’s not leaking or anything like that.

[@FlatironsTuning]

Thanks for the question. If your coolant hoses are collapsing, then it sounds like the 2-way valve on the cap on the expansion tank isn't opening. As a start, you would want to replace the cap on the expansion tank. You might also want to check the small hose that runs to the overflow tank to make sure it isn't pinched or blocked at all. If that doesn't help, maybe detail your burping procedure and we'll see if that gives us any ideas. Thanks for watching and Stay Tuned!

[@E85_STI]

@@FlatironsTuning I have the burp funnel and I use the green adapter and fill it with some coolant then I allow it to get to operating temp then I turn the heater on high and wait until I don’t see any bubble coming out. ( now I don’t run it for 20-30 mins I only run it for about 5 mins after the temp hits 185 with heater and the temp starts to fall then I end the burp process) My hose that goes into the over flow I removed it and flushed it and it’s the oem one so it has the slant cut on the end. I will make sure it isn’t kinked then order the cap but the coolant will flow into the over flow but it isn’t going back into the radiator after cooling.

[@4rct1c9Ic3m4n]

Wow good info. I actually thought these caps were interchangeable

[@FlatironsTuning]

Very glad that this helped. Stay Tuned!

[@HeidiFegles]

Well what’s funny is I think the second cap in Subaru is to eliminate the air pocket that forms and for some reason a Subaru water system is hard to bleed air out of. I am relocating my expansion tank and radiator cap to the high point so I can get the air out easier during refill or flushing coolant. And I use 1 cap and it’s a 2 way.

[@jukeboxzero1]

I bought a metal Mishimoto expansion tank for my '03 WRX. Their brand new cap (identical to the one shown in the video at 2:28 and 2:36) leaked so i replaced it with an OEM cap. I have new OEM caps on order to replace the 19 year old ones. Reference 4:45 it is stated that the 02/03 WRX did not have a radiator cap. I can't confirm or dispute that since i got a "free" radiator from my Subaru dealer when they poked a hole in it while replacing the timing belt. There are two caps listed for the 02/03 WRX: 45137FE002 Cap (Round) 45137AE00B Cap (Round with two ears to grab onto)

[@Silent_Keith]

I know the 02/03 only came with one cap, Subaru updated it with the 04 models (late 03 actually) due to radiator issues without the cap.

[@FlatironsTuning]

The 02-03 WRX didn't have a cap on the radiator, but that original part has now been discontinued and replaced by the newer radiator that has a cap. Thanks for watching and Stay Tuned!

[@jukeboxzero1]

@@Silent_Keith Bought mine in March '03. Wouldn't consider that a late '03 but maybe it was since i'm pretty sure there were caps on both the radiator and the coolant reservoir. And the original radiator survived without leaks for 13 years until punctured at the dealership. Page 11-20 of the owners manual refers to both a radiator cap and a reservoir cap but maybe that only applied to non-turbo cars.

[@tyree9055]

@@FlatironsTuning I can confirm that as my brand new 2002 WRX only had a "radiator cap" on the expansion tank.

[@jacquib5664]

I just had to replace the radiator in my 2010 Subaru Forester non-turbo. They put a new cap on my new radiator. However, I'm confused to which cap needs to be on the radiator now. The cap they have on it at the moment has two ears. Is this a two way cap. If so, do I need to replace this cap with a one way cap... without the ears.

[@FlatironsTuning]

Thanks for your question. Since your car is non-turbo, you shouldn't have the expansion tank. If you only have a single cap on your radiator, you would need a 2-way cap there. Hope that helps and Stay Tuned!

[@subielife306]

Heya great video thank you .! question if i may.. i have built myself a closed deck forged 2.0 ej and am running a aluminium aftermarket radiator with no cap . from what i am reading should i be running a larger expansion tank ie the mishimoto one with a 2 way valve ?

[@FlatironsTuning]

Thanks for your question. You do need to run an expansion tank then, and yes, you do want to use a 2-way cap there. We go into detail about this after we made that switch in this video: kzbin.info/www/bejne/iIi9hpd-h62em6s We have had good luck so far with the OEM expansion tank for what it is worth. Thanks for watching and Stay Tuned!

[@nova12332]

I run two oem 1.3psi caps on my forester xt, 1 for the tank and 1 for the mishimoto radiator. No issues after many years. I also did the same with my legacy specb, but with koyo rad this time. Still no issues. Just run 2 oem 1.3 caps

[@daddybotz]

Any info about koyo rads? I habe a 2011 wrx, installed koyo rad and bought the koyo red cap that says 1.3 kgf/cm2. Should I put this on the actual aluminum rad or expansion tank?

[@FlatironsTuning]

Thanks for your question. The Koyo caps are 2-way as well, so you should only put them on the expansion tank. Thanks for watching and Stay Tuned!

[@daddybotz]

Thank you! Great videos, more power to your channel and company!

[@dhwin5709]

I had a cooling issue due to running the mishi cap on a mishi radiator.. I think the main contributing factor is the expansion tank is the tallest point on the cooling system, therefore the two way valve needs to be there to allow coolant from the overflow tank to flow back into the cooling system properly. If you have a two way cap on the radiator, and a two way cap on the expansion tank.. then the coolant from the overflow doesn't have pressure to flow back into the cooling system.

[@dhwin5709]

@@Lennysuga agreed, but I believe the expansion tank is also supporting the coolant from the turbo.

[@FlatironsTuning]

Glad you were able to resolve your issue. Thanks for watching and Stay Tuned!

[@joshuaalvarado5188]

So I have a 2018 wrx with the mishimoto radiator and the mishimoto radiator cap… I have the stock expansion tank with the stock cap on it… I’ve been running the mishimoto radiator cap and my cars been overheating… could that be my issue ? Should I go back to the stock radiator cap?… I only have about 2 weeks with this set up

[@FlatironsTuning]

Thanks for your question. I would recommend putting the factory cap on the radiator and then burp the coolant again. Hopefully that helps. If you continue to have issues I'd recommend getting an experienced Subaru tech to look at the car. Hope that helps and Stay Tuned!

[@nrw510]

I was just about to order the radium engineering caps from you guys and I'm glad I didn't. Just going to use OEM caps and be done with it so there is no guessing on a freshly built motor. I see radium has a style A and a Style B. Is one of them a one way and the other a 2 way?

[@FlatironsTuning]

Thanks for your question Nick. As far as we can tell, all of the Radium caps are 2-way. Thanks for watching and Stay Tuned!

[@holeshot26]

i have a question about the pcv system. when i installed my IAG Competition AOS i completely removed my entire pcv system & just have all 3 breather ports ran into the AOS, and the return hose ran back to the crankcase breather port. Is my engine going to be ok without the pcv valve in said system, or do i need to reinstall the valve back on top of the crankcase breather port?

[@FlatironsTuning]

Thanks for your question. From what you have written, it sounds like you installed the IAG Comp. AOS following their instructions, which is correct. You do need to tune the car after doing this since you are removing the connection of the crankcase to the intake, but that is also why you do need to remove the PCV valve in this configuration. You should be fine with it installed as you describe. Hope that helps and Stay Tuned!

[@RX7Cody]

I called and talked to Mishimoto about this 5 years ago haha I had that Mishimoto cap on the expansion and a Koyo on the rad for awhile no issues but then switched to the Koyo on expansion and a JDM STi cap on the rad (yes mostly for looks on both) but no issues, have only pushed the car on a California canyon run, no track time.

[@FlatironsTuning]

Gotcha. Yes, now that we know what we are looking for, there is a bit of a pattern that is starting to appear. It is really interesting, and we are trying some new things now that we have this info. Thanks for watching and Stay Tuned!

[@RX7Cody]

@@FlatironsTuning yeah it’s surprising how much it impacts the timing and flow of the cooling system. Like on my FDRX7 the air separator tank has very cheap cap I wanted to change to a Koyo but the rotary cooling system is so fragile Looking forward to what y’all go with and find out 🤙🏻

[@FlatironsTuning]

@@RX7Cody Yep, this is a little bit of a game changer honestly. Knowing this, we should be able to make a small change or two and get the cooling system to work a heck of a lot better.

[@RX7Cody]

@@FlatironsTuning yup! 🤘🏻

[@DJ_Driven]

@@RX7Cody back when I had my 1993 RX7 R1 that factory expansion tank was known to just randomly explode. The hot setup was to convert to RX7 FC expansion tank delete setup.

[@emanuelhdez1468]

I need some assistance. I installed a 93 legacy mishimoto rad on my GC and do not have a cap. On my expansion tank, i have a 108k possible a 2 way valve cap. Im having overheating issues sitting in traffic. Is that the correct cap? Or is air in the system? Note: Is a new build

[@FlatironsTuning]

Thanks for watching and thanks for the question. If you just put everything in, the most likely issue is that you either have air in the system or the cap is not working properly. Most auto parts stores can test radiator caps, so I'd recommend starting there, and then burping the cooling system again. If you see any signs of air coming out, that is most likely your problem. Hope that helps and Stay Tuned!

[@emanuelhdez1468]

@FlatironsTuning looking at other forums, it looks like i need an overflow tank to deposit or retrieve coolant from. If that's the case, that may be where the air is coming from.

[@FlatironsTuning]

@@emanuelhdez1468 Yes, you definitely need an overflow to hold the coolant as it expands. If you don't have that, and are simply letting that coolant escape, that is most likely where the air is coming from as you say. For reference: kzbin.info/www/bejne/g3O5f3uFg5iXZtksi=zWompe3CiJ-TWiQY

[@armandsantana7152]

Can the turbo legacy radiator cap (137 kpa) work on the non turbo radiator?

[@FlatironsTuning]

Thanks for your question. Generally speaking, the non-turbo Subaru's only have one radiator cap, so you would be best to use their factory cap, not the Turbo cap. Hope that helps and Stay Tuned!

[@nrw510]

OEM Radiator Cap www.flatironstuning.com/subaru-oem-radiator-cap OEM Aux Tank Cap www.flatironstuning.com/subaru-oem-aux-coolant-tank-cap

[@FlatironsTuning]

Thanks for those links Nick!

[@ANL4JC]

So for a rotated setup without an expansion tank use the stock cap or aftermarket 1.3? 1.5? Curious

[@FlatironsTuning]

If you only have one cap on the system, it would have to be a 2-way cap. So any aftermarket cap would do. If you ran a 1.5 bar cap, then you would be increasing the pressure of the system. Hope that helps. Stay Tuned!

[@ANL4JC]

@FlatironsTuning makes sense. Increasing the pressure with only one two way cap is good or bad?

[@FlatironsTuning]

@@ANL4JC Well, I would say that when you only have one cap, it must be a 2 way cap so that you will be able to let coolant back into the system when the engine cools off. The advantage of a single cap is that you now have control of the pressure of the system with that single cap. So if you want to increase the pressure, it is easy to do so. Increasing the pressure will slightly increase the cooling capacity of the system. Just make sure that everything on the cooling system is tight, etc. For instance, we are running a 2.0 bar cap on our race car, but we had to test the system integrity to make sure that it would hold at that pressure. You might want to take a look at this follow-up video: kzbin.info/www/bejne/iIi9hpd-h62em6ssi=JvWm1mQgA9jskjXD Hope that helps!

[@DandCentertainment]

For clarity, with an AM Radiator like the Mishimoto, can I use the Factory Caps in both locations; Radiator and Upper Reservoir?

[@FlatironsTuning]

Thanks for your question. Yes, you can use both stock caps with a Mishimoto radiator. Thanks for watching and Stay Tuned!

[@marcodg301]

Please post the a as soon as you have figured out the best combination 😅 . Also since the expansion tank is a plastic one , which aluminium aftermarket one would you recommend ? Ths from Italy

[@marcodg301]

***post the video....

[@FlatironsTuning]

Another video is in the works :-) Thanks for watching and Stay Tuned!

[@kchanguito]

Flow Dynamics can also cause issues , (modify) engine usually Create way more heat than the (block ) was engineered to dissipated/ pressure /flow may have a max efficiency with the infinite variables of block differences , Maybe equalizing flow with a (4 cylinder cooling mod ) I currently have a expansion tank deleted with an AOS as *high point, with radiator cap* after market radiator . it pulls and pushes coolant in to the reservoir no problems or overheating has occurred

[@DJ_Driven]

So basically you deleted the expansion tank and running the iag race version AOS with aftermarket radiator and original factory radiator cap correct?

[@FlatironsTuning]

Thanks for watching and Stay Tuned!

[@kchanguito]

@@DJ_Driven that is correct , so no issues as of now there is a few other factors but related to this video that is what I’m running

[@tbas8741]

Also my 99/00 model WRX GF8 Wagon has Metal end tanks on the radiator and so do all the other proper WRX's 1994-2000

[@ttamn92]

They never tought us anything what so ever about this in subaru factory technician training courses... I must have been very lucky over the years because I ran installed and sold tons of sti and greddy radio cap sets and never had an issue...that I was aware of anyway.... but makes a ton of since tho knowing the difference and how each work

[@FlatironsTuning]

Thanks for the comment and thanks for watching. Very glad that the video was helpful. Stay Tuned!

[@admireinspire]

Is that the marsh composites reverse scoop hood I see in the track footage? Man I ordered mine in march last year so I should be seeing it soon? I hope? 😂🤞

[@FlatironsTuning]

Thanks for the question. Yes, that is our Marsh Composites hood. So far, we really like it. With a couple small adjustments to the cooling system, it should take our cooling system to the next level. Thanks for watching and Stay Tuned!

[@kongowns7446]

I'm still confused on the radiator caps. i have a Mishimoto radiator and I have the Mishimoto cap on the radiator and it seems to run fine. should I do what Mishimoto suggested and swap the OEM expansion tank cap on to the radiator and the Mishimoto cap on the expansion tank?

[@FlatironsTuning]

Thanks for the question. Ideally you would run the stock caps honestly. If you were to use the Mishimoto cap, it would go on the expansion tank, and then the OE RADIATOR cap would go on your Mishimoto radiator. You need the 1-way cap on the radiator. That is the piece that is most important. Don't put the expansion tank cap with the "ears" on the radiator. It is too low pressure, and is also a 2-way cap. There is a reasonable chance that having the higher pressure cap on the radiator is okay. (Mishimoto cap is 1.3 bar, and the OE expansion tank cap is 1.1 bar). But you may still have issues with 2 2-way caps. Hope that helps and Stay Tuned!

[@PeterHernandez-lg2eh]

Do I burp air at the expansion tank or on the koyorad radiator cap ????. I just did this on the koyorad side. Was this wrong ?

[@FlatironsTuning]

Thanks for your question. Because the expansion tank is the high point, you would want to burp the coolant there, not at the radiator. Hope that helps and Stay Tuned!

[@PeterHernandez-lg2eh]

Very helpful muchas gracias

[@andrewhorry9417]

Hello guys so which cap should have the higher pressure the one on the expansion tank or higher level cap or the pressure relief valve that Subaru calls it which is the radiator cap that's in front of the car

[@FlatironsTuning]

Thanks for the question. The cap on the radiator needs to be higher pressure than the cap on the expansion tank. Thanks for watching and Stay Tuned!

[@andrewhorry9417]

@@FlatironsTuning thank you so much for your response love the channel my last question to that vain the higher pressure cap that goes on the radiator in front of the car should that be two-valve or one valve. From your videos I gather the two-way valve cap should go on the expansion tank which is the highest point of the car please confirm

[@FlatironsTuning]

@@andrewhorry9417 Yes, that is correct.

[@1_Bad_Z]

Dealer OEM caps on Japanese cars gor for about $20. give or take. Seems pricy compared to local auto parts store that are $5. However, dont cheap out on caps. If you are going after market buy a good quality cap. It may cost you about $25. But again, dont cheap out. I use the cap that goes on my Megan racing radiator 1.5 years later. No issues at all. I do keep a Honda oem cap in my glove box for backup.

[@dawincebee]

I know I’m late but the consensus is to just run the stock radiator caps with any radiator?

[@asdreww]

I have the early STI style single cap system & really can;t understand the disadvantage - pretty much all cars have a single 2 way rad cap.... I thought the additional cap added to the radiator was purely because some people weren;t patient enough to bleed the system properly.

[@FlatironsTuning]

Thanks for the comment. It turns out that the addition of that cap can cause a lot of issues if the proper cap isn't installed. The single cap is a much better solution I'd say. Thanks for watching and Stay Tuned!

[@PeterHernandez-lg2eh]

Mucho confusion with 2 caps

[@ryandrews9612]

I fully sealed and capped off my mishimoto rad cap so it won’t allow anything out. Kept oem cap on upper reservoir and it’s been fine ever since.

[@FlatironsTuning]

Thanks for watching and Stay Tuned!

[@tfaubus]

What's funny about my ej255 with mishimoto rad and proper cap, plus oil cooler, on track I still purge coolant, even though I pass a pressure and exhaust gas test, never overheats though 😜 i just have to pour the coolant from the overflow back into the top tank, then let er rip some more.

[@FlatironsTuning]

Thanks for your comment. I might recommend trying factory caps in both locations to see if that makes any difference. But glad to hear that you aren't having any more serious issues. Thanks for watching and Stay Tuned!

[@tfaubus]

@@FlatironsTuning yeah note that I believe running 19psi caps in both places is ok, I did start with new oem cap on the rad and the mishi cap up top, BUT i noticed the clamps on the Mishi cap were not sealing well due to incomplete clamp of the tangs, nothing my bench vice couldn't fix :)

[@732ajay]

So can you leave both caps oem or do you have to run the mishimoto cap on the expansion tank?

[@FlatironsTuning]

Thanks for your question. Yes, you can run both OEM caps. If you were going to use the Mishimoto cap, you would only want to put it on the expansion tank. Hope that helps and Stay Tuned!

[@osmanamin6621]

Hy my subaru has 2 caps the radiator cap its written 1.1 abd the one on the engine its 108kpa. What if i put both 108kpa what will happen coz i can only get 108kpa??

[@FlatironsTuning]

Thanks for your question. I'd look at the bottom of each cap to see if they are 1-way or 2-way caps. Make sure that the 1-way cap is on the radiator, and then see if you can find the Subaru OEM 1.3 bar 1-way cap. Here is a link to that on our site if it helps: www.flatironstuning.com/subaru-oem-radiator-cap Thanks for watching and Stay Tuned!

[@thenuge88]

A couple of years ago I got a radiator flush at a Subaru dealership and they accidentally swapped the cap locations when they were done. Started hearing intermittent burbling noises in the dash and discovered what they did 🤦🏻‍♂️

[@FlatironsTuning]

Ouch. Glad you were able to find the issue quickly and fix it. Thanks for watching and Stay Tuned!

[@petrmiskerik]

And what is the route with koyorad ? Is the same ? Is koyorad coming with his own radiator cap ?I don't wanna mishimoto rad on my STi...

[@FlatironsTuning]

Thanks for watching and thanks for the question. Yes, same for the Koyo cap. It is a 2-way cap, so you should only put it on the expansion tank. The best cap for your radiator is the OEM cap. Hope that helps and Stay Tuned!

[@petrmiskerik]

@@FlatironsTuning Thx a lot guys. You are the best. I am proud of being part of subaru community / especially thanks to you.

[@Devilpeakmotorsports]

So, if the reason Subaru put the second cap on the radiator was to keep the seams between the aluminum core and the plastic from leaking, why does the all aluminum aftermarket radiator need it?

[@AmirPomen]

So the overheating issue is solved? Im surprised.. lol... Anyway i often see people swap aftermarket radiator cap...whenever they swap yo aftermarket radiator... which i will always try to make sure that higher pressure cap installed on radiatot.. not the expansion tank... Because ive alway have this thought that with expansion tank.. u dont want coolant going out somewhere else at lower pressure than the tank... So with this service manual on 2types of radiator cap story... These explain further and support my theory on this.. Thanks for bringing this up 🍻 cheers

[@FlatironsTuning]

Thanks for watching and Stay Tuned!

[@lam3huynh]

So what do you recommend for 2006 STi with Koyo Radiator?

[@FlatironsTuning]

Thanks for your question. The Stock caps would be the ideal option for most applications. At a minimum you want to keep that OE one way 1.3 bar cap on the radiator. Thanks for watching and Stay Tuned!

[@Segar1991]

So the stock expansion tank cap, it is already a 2way?

[@FlatironsTuning]

That is correct. And it needs to remain a 2-way cap. Thanks for watching and Stay Tuned!

[@Segar1991]

@@FlatironsTuning thank you!😎

[@dsxmotorsports]

freaking mind is blown

[@FlatironsTuning]

Then my job here is done :-) Stay Tuned Ryan!

[@SuperJuniorja]

Can the expansion tank be deleted? And what would the effects be

[@DJ_Driven]

Josh at BBR pretty much does it to all his cars by deleting the expansion tank and running a iag race version AOS that is then the high point in the cooling system. Pretty sure he uses the factory 1-way cap on the radiator with that setup but have not confirmed this.

[@FlatironsTuning]

We are going to get into this in the next video. The short answer is no, and bad :-) The expansion tank is actually the key to the solution I think. Thanks for watching and Stay Tuned!

[@johnmastr7901]

The mishimoto cap must be a lower pressure cap the the expansion tank cap, otherwise why even use mishi cap?

[@FlatironsTuning]

I think that the 1-way and 2-way configuration still matters, but yes, the pressure stagger is almost as important. It is likely that without making other changes, the ideal option is to stick with the OEM caps. Thanks for watching and Stay Tuned!

[@vader2774]

I have a jdm 99 gc8 sti it only has one cap on the top turbo tank and the radiator has side tanks no failures yet 205,000km going strong

[@PeterHernandez-lg2eh]

How about the koyorad radiator?

[@erickvargas5427]

Im on my 3rd cap setup and overheating. This should my next try.😒

[@FlatironsTuning]

Thanks for watching and Stay Tuned!

[@0236king]

Why doesn't mishimoto just make a single way cap that we can buy?

[@FlatironsTuning]

Or anyone else for that matter. They are way, way harder to find that we would have expected. And I suspect the issue is how unusual a 1-way cap is generally speaking. Thanks for watching and Stay Tuned!

[@georgenickolas7321]

As you do research I think Thomas said he doesn't run radiator cap on his radiator

[@FlatironsTuning]

Thanks for your comment George. You are correct, and he has helped to point us in a good direction with the system as well. Stay Tuned for another update here soon.

[@georgenickolas7321]

@@FlatironsTuning Also what aftermarket expansion tank works well for rotated turbo guys

[@FlatironsTuning]

@@georgenickolas7321 It sounds like the Radium expansion tank would be one to look at. It is a bit large though, so you would have to make sure you have room for it.

[@jordonhaberer434]

I’ve had issues with radiator caps a few times myself.

[@FlatironsTuning]

You sir, are not alone :-) Thanks for watching and Stay Tuned!

[@MrLifeEclipse]

I have a fully built EJ25 making nearly 700 WHP and happen to come across this video only to find out my caps were swapped. 😳

[@Rick4345]

My 22 WRX only has one radiator cap. At least the only one I can see.

[@FlatironsTuning]

Yep, that is correct. With the turbo now mounted at the bottom of the engine, you don't need the expansion tank any more. Thanks for watching and Stay Tuned!