Differences Between Expansion Tanks & Overflow Tanks in Automotive Cooling Systems

[@QuigzDrifts]

Great video, no intro, jumped right into it, explained it concisely. Learned more in 3 mins then I did in 10 mins of google/forum searching lol

[@ashleysnyder4875]

I just want to say thank you. I bought a car with an expansion tank and NEVER could find anything like your video to explain WHY I didn't have a radiator cap and what more, how each was used. Bravo! 👏❤

[@ThabangMolapo-t6v]

Some vehicle's don't have a cap on the radiator you only refill water on the expansion tank

[@kirkgarner7381]

Great video and explanation. One important difference between the two (that I learned the hard way) is that you can open the lid on an overflow tank while the engine is hot but you should never open the cap on an expansion tank while the engine is hot.

[@JohnDoe-iq4kz]

0:48 - If there is vacuum on the left side, WHAT is gonig to compress the spring in the radiator cap to allow liquid in the reservoir to come back into the radiator ?

[@drbeastcar2992]

I came here looking for this answer

[@mohdkitt9083]

Its about heat and cool.

[@georgehooper6955]

Same question. That valve will be held shut by both the spring AND the vacuum pulling on it

[@lukew9033]

Wondering the same thing

[@Gyppor]

Awesome, thank you for the description. I've worked on cars for 2 decades but never had to do much on coolant systems, this helps a lot!

[@tonyvang7080]

Good job on the explanation. Keep note that the bigger spring on a pressure cap is named pressure spring. Then, the smaller spring is named vacuum spring.

[@johnlotherington8436]

Hi just wondering on the top picture , should the cap be Return or Non Return cap ? Thank you as I thought it should be Non Return but the shop is saying should be Return , where I thought it should be Non Return …. Thank you 0:22

[@jpleroux5951]

Is there a difference in pressure between these two systems? I know that the cap determines the pressure in the radiator but can you adjust your pressure with the expansion tank setup?

[@RzVids]

There’s a cap on the expansion tank

[@AndyNav1]

Thanks for this educational video. Question for you: Coolant overflows only sometimes not always after a drive on my ML500. I have no overheating, heater works perfectly; and this doesnt happen after every drive. Your guidance is much appreciated.

[@Babybeast4357]

How does the coolant flow back into the radiator past the radiator cap when the pressure of the cap pushes down on radiator creating a seal? I’m not comprehending the return flow from the reservoir to the radiator!?!?

[@VC279]

Hey, an you explain why there is a return line on a expansion tank that sends coolant back to the pump? My tank has 3 connections, 1 to the radiator, 1 to engine outlet (behind the thermostat) and 1 connect just before the waterpump. Isn't there a bypass to the radiator in such a design? I'd like to understand why it was build that way and whats the purpose. Thanks!!

[@JeffSmith-dv2zb]

Great explanation. I had wondered by my BMW could have small hole built into the top of the coolant tank, when most websites I saw said that the coolant tank is pressurized and part of a closed system

[@pjames4413]

Does your car have an actual radiator pressure cap on the radiator. If so the coolant tank is an overflow tank.

[@burningapartmentbuilding]

i was curious as to why coolant level goes down in the overflow tank as the car sits and cools down. Didnt know if it was okay and normal. This video helped

[@jb-ik8sj]

At the end of the day the fluid flows back into the radiator?? Doesn't the spring on the radiator cap also cool down and closes. So how can atmosphere pressure push the fluid back in with the spring deactivated?

[@georgehooper6955]

My question exactly! When the engine cools down, there will be vacuum from the engine pulling the pressure valve closed, plus the force of the spring. How does coolant get back into the radiator? (Overflow bottle type system)

[@jb-ik8sj]

@@georgehooper6955 2 different spring systems. I had no idea a radiator cap was that technical...

[@ThabangMolapo-t6v]

Question there are vehicles that uses an expansion tank with two hoses the other one is return then the other one is coming from the radiator so on that type of model how does it build up pressure?

[@HillyRoads]

Steve if you have an older model vehicle and extra coolant, would it make sense from a preventive maintenance standpoint, to extract some or all of the overfill coolant and replace with new coolant, pre Summer?

[@CarsSimplified]

Even if the coolant was being replaced directly from the radiator in the amount the tank has, the old and new coolant still mixes into a less ideal mix, and very little of the sediment that needs to get flushed out will be removed. An overflow tank being drained and filled with fresh fluid would be like that but the mixing would occur much more slowly, potentially not at all if there is an issue with the cooling system. It wouldn't hurt, but it would be much better to just drain all the old stuff out and put in all new fresh coolant. Plus you avoid potential coolant compatibility issues.

[@HillyRoads]

@@CarsSimplified yeah you must be right because I've never heard of anybody doing it thanks for the feedback

[@jhtprojects4431]

Very clear, the difference between the two designs. Thank you. Question, with an expansion tank design, can I gradually "change" the coolant by siphoning off the contents of the expansion tank and pouring in new coolant, say, once a week or per month? Thank you

[@CarsSimplified]

Thanks! As for your question, that would maybe have a slight effect on the condition of the coolant, but it would keep bad coolant in the system for a long time and you wouldn't get one of the major benefits of a full flush: clearing out the sediment. Good question though! There are some service chemicals that get changed in a similar manner to what you described.

[@badressam473]

In the upper system with the main cap on the plastic bottle can i add another tank to match the other system and to refill the the system if needed

[@ZSnowman]

I landed here just because I was wondering if the head gasket testing kit could be utilized in either system through either the overflow canister or the expansion tank. I'm trying to be extra safe when checking out cars before purchase. Thanks in advance for any information.

[@jd646]

If your overflow tank isn't pressurized, then you must use it in the radiator 😊

[@alessiocarlevaro6934]

Does the position of the overflow tank matter? let's say i want to move the one that came with the car, do I have to put it higher/lower than the radiator or can i put it wherever? Thank you!

[@galloarepa]

Great vid. My Cap seal broke and fell into the radiator, causing my overflow to leak a lot of water. Should I worry about the seal being stuck in radiator and obviously I need a new radiator cap? Thanks!

[@gavinwilliam11]

Hi, Very informative. Can you use twin expansion tanks with twin overflow tanks if you are going to run dual radiators?

[@labradormcgraw]

Just found this channel - not too sure how I've missed it. This was very clear, thank you. Subbed from London.

[@txrankin5]

On the bottom design...As the coolant heats up and pushes past the seal on the radiator cap, how does the coolant get past the seal on the radiator cap when it cools back down?

[@CarsSimplified]

Good question! Definitely something I wish I included in this video. I'll end up taking one of those radiator caps apart sometime for a future video, but on some of these radiator caps there's a small sealed way back in that has a small spring holding it shut. As the coolant in the working part of the system cools down, the pressure can get low enough to overcome the spring and pull the excess coolant back in. When the cooling system is at a neutral pressure, just the spring seals the cap, and when the system is pressurized, the pressure and spring are both keeping that return path pressed closed.

[@sherwinmoquia204]

I see in my mom's Hundai Starex it has an expansion tank system built to it. I suppose it's normal to see the coolant boils while the engine is running, correct?

[@stephenchua2576]

Been looking for a flow diagram for a cooling system with expansion type (specifically Hyundai Tucson). Can you help?

[@jeanngandumushinde4820]

Is the Toyota hiace van (with 5L diesel engine) has an expension or an overflow reservoir. Explain how it works. Thx

[@madetoremain]

HI - i have Chevrolet epica 2009 with 2.4 6 cylinders engine - i remove the old engine and install new Toyota Camry engine every thing is great but i want to know Do i have to change the RAD system from the original one ( expansion tank ) to Over flow type ? Thanks

[@patriotcan4165]

I have question what If I filled the resovoir with one jug a pure antifreesze and did not mix.Can I still fix the mix to get right ratio?

[@CarsSimplified]

You might be able to if there's enough room for the water. Most personal vehicles I can think of don't have two gallon reservoirs, though. You may have to drain/extract some of that full strength stuff.

[@finalmatrix]

I am thinking, for the pressurized system, if I release the pressure when coolant is hot with care, then when coolant is cool, it'll create vacuum. Next time it gets hot again, the PSi won't be as high as usual. Is this a good idea to have constant vaccum in coolant line? I've seen coolant hoses got blown holes in them. The goal is to prreserve the coolant hoses. Thanks

[@desitrader7827]

hello, thanks for t he video. it is very useful. On my 2004 acura is blowing off the reservoir plastic cap, This car has a spring loaded raditior cap. what could be reason. is it ok to drive without platic cap. Dealer asks 15 dollars for it?

[@vallan8491]

Do you know why my nissan frontier has a pressure cap on the radiator and the overflow reservior? How necessary is the overflow pressure cap? Reason: I wanted to change my reservoir to the aluminum reservoir with the vertical tube that clearly shows fluid level.

[@jelzkie8351]

May I ask if hoe to bleed the expansion tank? Thank you for your time

[@kandygillen1107]

Question. Why does the expansion tank on a ford e350 have 4 separate compartments in it

[@anthonybowling57]

Does the expansion tank circulate with the radiator circulation.

[@kulas4024]

Hi Thank you for making these videos I have a question about my car, the coolant is in the minimum before using it, and dropped a little bit after using. It retains that level until morning and when I opened the cap it came back to min level. Is that normal?

[@Luc3ntiX]

Is it normal to see some bubbling in the reservoir with the car showing normal temps ?

[@oscarfoxman785]

Can I convert an expansion tank style to an overflow? I ask because I have a Power Stroke with an expansion tank (degas bottle) in a very inconvenient spot.

[@clayyng]

Question, my truck had an expansion tank from factory and switched to an over flow style tank from a 90s-2000s mustang. Since there is no way for the pressure to be released could this be the reason for coolant pushing past the overflow tank cap and spraying out when I am racing for one consecutive long time/run? Doesn’t over heat or anything just pushes past the cap when i do lets say a 60-130mph runs.

[@kippd2265]

I have a 2012 GMC sierra. Does the coolant circulate through the expansion tank is my question… Just added some coolant after I fixed a radiator leak and I want to make sure that the proper ratio is flowing through the system. It still looks like pure coolant on the expansion tank, even after driving for a while…

[@pearlbest5109]

Do 1971 Lincoln Mark 3 have overflow radiator container?

[@ssalamri7302]

hey man what happened if I put a little more coolant in flow tank?

[@mr1hander]

theres a center valve in the caop that allows water to run back into the system, the vacuum created by the system as it cools..us what pulls the coolant back in from the overflow tank

[@shortybarrios8310]

So does placement of the overflow tank matter then? Or is it traditionally lower than the radiator

[@kdrymn]

One question. Is the level of warm coolant higher or lower then cold coollant. Because the level in the expansiontank looks as it is rises at warm temperature en lowers at cold temperature. Is this correct?

[@CarsSimplified]

On every one I've seen, that has been true (that the warm level is higher). Not every tank has high temperature and low temperature marks, but it will still work that way, marked or not.

[@stevezielonko1386]

Whats the best method to clean the gunk out of them????

[@Duchydog]

In an expansion tank system -is it correct that the coolant does continually circulate through the entire system (including the expansion tank) when the vehicle is at normal operating temp?

[@ronaldsteveson76]

I have a lengthy question. On my 5.3 swap in my 64 C-10 I installed the surge tank from the 03 Tahoe the engine came out of but not the radiator. I also installed the correct heater hoses to the surge tank. My problem I essentially have two radiator caps now and I can't seem to get the air out of the system. Running the vent line under the radiator cap of my LS swap aluminum radiator to the outlet on the surge tank that normally goes to the stock Tahoe radiator. I'm doing this via a reducer in that line. Thank you for taking the time to read. Great video BTW 👍

[@joselperez9384]

Can i install an overflow Reservoir to a system that uses expansions tank?

[@paralelmind]

Hi! Is there a problem if I go to a higher pressure coolant tank cap? For example the cap on my car (a4 b9) has 1.4 bar and want to change the whole coolant expansion tank with a new cap that has 1.6 bar release pressure. Thank You!

[@vallan8491]

my nissan frontier has a pressure cap on the radiator and the overflow tank with a pressure cap, do you know why? I wanted to change it to the aluminum tank with the clear tube showing levels.

[@5t341tH]

I made my own radiator overflow tank since I have a custom engine swap. My question is, should the cap be a tight seal or should it be vented? Currently I have an aluminum container with a twist on cap with a rubber seal on it

[@elbale2323]

I have downflow radiator and stock overflow tank. Can i put a swirl pot sir? What are the benefit?

[@ProJanitor]

When adding coolant to an expansion tank while the engine is cold, do you fill until level is at min, max, or in between the two?

[@ThabangMolapo-t6v]

What will happen if the spring of the radiator cap closes while the coolant it is full in the overflow tank isn't it going to overheat?

[@busterstig7830]

I've got a 1.4 petrol corsa and my water tank has a return nozzle at the top but no pipe attached so what does that mean?

[@brightonmusic]

Very interesting! My 2016 Chevy has a different configuration. Both my radiator and surge tanks each have a pressure cap. When the dealer did a flush recently, when the car is cold, the fluid in the surge tank is all the way to the top. I'm concerned about what happens if it gets hot. Where will the excess coolant go?

[@carbonm2]

It'll come out through the hole below the cap. It's VTA

[@brightonmusic]

@@carbonm2 Thank you! That's what I am concerned about. I wouldn't want the hot liquid going on wires or any electronic components. With your information, I am now doubly glad that yesterday I used an old Turkey baster and removed the excess.

[@markzachmann2688]

On the expansion tank explanation, you mentioned that some systems have a return line. I'm wondering if you have any examples of systems that don't have a return. Seems like across the board if they have an expansion tank they have a return to somewhere just before the pump. I don't really know why they need a return, but it has to be doing something. Maybe keeping some small amount of flow up and through the tank continuously purging air?

[@johnlotherington8436]

My tank has a med to large hose to radiator then I have 2 small hoses from tank to radiator 2:31

[@tdbofamerica]

If you have a low mount radiator with an expansion tank that links to a thermostat housing/fill neck - what PSI caps would go on the thermostat housing and expansion tank? Eg if 16 psi cap is normal - would I do 8 and 8 in each location or 16 in each?

[@steveh8724]

Very nice clear explanations, thanks for posting!

[@M3GAN3116]

How often should you top off coollent ? I live in desert thanks

[@manuelcalvorodriguez5993]

Great explanation and I really thank you for your time. I got a question: what happened if I just install an expasion tank instead of a overflow tank (radiator has already its cap) would it work as "overflow"? The issue is that I am rebuilding an old truck which has no overflow tank at all (there is just a hose from radiator to space) so I have to keep checking for the coolant level as it drops it when heats up, because of the place where the overflow tank supposedly fits it is kind of weird that only found an expansion tank that would fit in place .. let me know what do you think would ya? Thanks in advanced man. Atte MC.

[@MOAON_AABE]

Can you flush and REFILL coolant through the expansion tank (top picture) because my car does not have a typical radiator cap??!

[@chrisspain7776]

The drawing shows the two tanks place at two different levels (heights) but you didn't mention whether that matters. Are you familiar with the term "header tank"? My understanding is that a header tank contains a "head" of coolant above that in the radiator so that gravity plays an important part in its operation and is preferable to the two you have covered.

[@mirriamdube5162]

What causes the expansion tank to be full with coolant and split coolant out leaving the radiator with less coolant thanks

[@caly5328]

On the expansion tank, where does the lower hose go?

[@hamdihamdy1156]

Is it possible to change from open to closed in any cooling system.

[@VINICIOMAGI]

Thanks so much for the video. I have a C7 corvette and am wondering how the engine cooling system gets pressurized. If it is so. Now in the expansion tank there is an overflow hose connected directly to the ambient. So, the pressure cannot increase in this tank. In any case there is a 20 psi cap. Maybe it's there for safety reasons. But my main concerns are with the pressurization of the engine cooling system. How can the pressure increase due to this venting in the expansion tank? What do you think?

[@chrisspain7776]

In a pressurised cooling system (i.e. most cars), as the coolant heats up it expands, and pressurises the air inside. If the coolant level is high enough, so that there is little air volume the pressure will exceed that of the cap rating (typically about 15 psi) and the cap will release any air and/or coolant. If the coolant expelled is captured in an unpressurised overflow bottle, then some or none of it may be returned but this depends on certain conditions such as the height of the bottle, and whether the end of the pipe is in or out of the coolant. I hope that helps?

[@apuwdm2]

Excellent video.

[@selvaszf]

during negative pressure how it will work

[@lemere]

In the first illustration of the pressurised radiator with an expansion tank at atmospheric pressure, how can the coolant be drawn back into the radiator against a seal with a strong spring?

[@Yahgiggle]

has a type of valve on the radiator cap that lets the overflow coolant back in as the cooling of the coolant cools it causes a vacuum that makes the pressure inside your sistem lower than the air pressure outside, and this push's the coolant back through the valve in through the radiator cap back into the system, this valve lets pressure out of the system when it gets to about 15psi ish to 18psi ish but about 0 pressure needed to push the coolant back into the system, well not zero but its 14.6 witch is our atmosphere pressure, so it wants to return to 14.6psi this is why it push's it back in and not sucks it back in

[@jettisonyurei8809]

very informative, thank you. i was playing "The Long Drive," a driving survival game and was just curious how my coolant tank was working just by putting a liquid in it. i will be watching more of your videos, sir.

[@CarsSimplified]

Thanks! I like both driving and survival games, so I'll have to look into that one!

[@stevebutler812]

Game only $10? Seems interesting

[@patrickdubuc3439]

Does the overflow have to be vented or can be completely sealed?

[@tradeswithjohnnie]

Perfect explanation. Thank you for making this video

[@jesseg573]

I have a 454 everytime i use it for bit then turn it off it always leaks water I always have to fill up the radiator w/ water b4 i use it, it doesn’t drain all the way just a bit after a couple uses it gets pretty low any ideas on what i need

[@Mike_44]

I recently replaced the radiator on my ‘19 Chrysler Pacifica. Afterwards, I burped the coolant with a big funnel, but now the coolant level on the expansion tank is a bit high. Soon as I open the cap it makes a whoosh sound and the coolant level drops about 1.5 inches. The coolant temperature ranges seem to be ok 195-225, depending if it’s seating idle on traffic or moving. Do you think I may still have air in the cooling system? Should I repeat the burping process??

[@seemann0815]

Thanks for that. Now I understands the difference.

[@Lou1ouze]

Thank you ! great info!

[@wilfreddaviskamau8948]

What would be possible causes for the overflow coolant not being drawn back in to the radiator? Other than a faulty radiator cap that is.

[@Arupojonu]

In case of an overflow tank (open type system), the tank has a way of breathing air in and if that way gets shut (e.g. due to a clogged hose or a loose tank rubber cap seal getting sucked in the outlet during engine cooldown), then the expanded coolant will not return to the radiator. If this happens a few times, then the radiator will loose so much overflowed coolant that the car will overheat and eventually blow its head gasket. So, in open systems, what you describe, might happen due to faulty overflow tank cap and its hoses/seals.

[@great4ever845]

​@@ArupojonuI have coolant on my radiator cap bit nothing in the reservoir tank ?

[@sancheztorres35]

I have a sonic 1.4 and the reservoir tank cap say 20psi so if i use a 16 psi cap Is any problem with that or could be a good thing???

[@Arupojonu]

Nice video, thank you.

[@gennadiyfriedman9741]

great video - thanks! question: my car's engine can't reach the operating temperature, even after some time of driving. I also don't see the coolant swirling in the expansion tank as it used to before when it start circulating through the radiator. What could be the reason for it? thanks!

[@alanhillyard1639]

Hope you figured your issue out already but sounds like you have a coolant leak that has reduced your coolant level to the point that there is now no coolant where your temp sensor reads the coolant temp. If you didn’t fix it I’m guessing you might have ended up with head gasket issues? Probably started out with a perishes hose somewhere in the system

[@karenthomson9749]

Remove half the coolant place one cup of milk in and then 50 grams of rocks. You’ll be gtg.

[@karenthomson9749]

@@alanhillyard1639 see my comment for the solution 👍🏻

[@cal.or7]

So it bleeds itself?

[@santhanakumarimohan]

Hi There are some special coolants that does not boil at around 100 degree celcius but boils at much higher temp like 160 degree celcius. If we operate with such coolants the radiator system does not work under pressure. In this case do we need expansion tanks?

[@oddjarlelvold3496]

Om fixing a 1988 Cadillac. There is a little bit leak om waterpump, and the owner told he check the owerflowtank often. But Wien i checked the radiator, i filled it up with 2 gallon. So why did the coolant not go to radiator from the owerflowtank?

[@hermanotan6132]

Hi from Australia. I own a 2005 Toyota Altise. Coolant is leaking from the Reservoir/ over flow tank. Mechanic has adjusted the hose and placed a clamp on the hose next yo the reservoir tank. Why is it leaking?

[@ricardodizon9148]

If I lost the cap what prblem

[@davidroberts8210]

i replaced the radiator, with a new one the water pump and thermostate in my 09caravan coolent level drops and does not get sucked back into the radiator, i must add coolent to radiator to keep it from overhaeting. no white smoke no coolent in oil what should i be looking for van has 149k i am thinking vally pan gasket

[@rodolfocastanos4341]

How should i drain a traditional coolant system. I have a 2016 corolla.

[@joseph2095]

'05 Town and Country 3.3L Overflow tank fills but doesn't seem to ever return any liquid to the radiator. Radiator level decreases. What would be a fix for this? I've changed the cap, no apparent result. Could there be a leak in the cooling system?

[@paddy145214]

Hi, I have a race car with an expansion tank set up, however the expansion tank has a pressurised cap without a valve and the radiator has a valves cap. The valves cap on the radiator is vented to nothing which gets messy. It didn't used to get messy but I'm getting overheating issues ( possibly head gasket) but not sure. Have you seen a system like this before and am I a component missing? Any help appreciated.👍

[@AbdulKalam-qh8ue]

Hi I did a coolant flush on my passat b8 and put in 4 litres of coolant. I realised it wasn't enough but my mechanic said its fine you can drive it. It covered 2 inches of the bottom of the expansion tank but after 10 minutes of driving I realised my expansion tank was empty. My engine fan did not turn on my car did not show signs of overheating on the temperature gauge. Is there a chance that I have damaged my engine?

[@PeaceChanel]

Peace.. Shalom.. Salam.. Namaste.. 🙏🏻 😊 🌈 ✌ ☮ ❤

[@user-xw6zj8nt1w]

I have a problem with my reservoir tank ,anytime I’m pouring coolant in the main tank it always go to the reservoir tank ,till the reservoir tank full up. When taking the water back from the reservoir tank ,the main tank also go down ,ant help .? It make my infinity qx56 2004 always get overheating, please I need help

[@BrianCanady-u1c]

Marvelous way to break it down and to explain it Numbers 6:24-26 24 “The Lord bless you and keep you 25 The Lord make His face shine upon you, And be gracious to you; 26 The Lord lift up His countenance upon you, And give you peace. God bless

[@louieflores590]

Sir can I ask something about my ford ranger expansion tank. I went into a shop to check my ford ranger because I am losing significant amount of coolant and they haven't fount any leak. They said that my expansion tank is not generating pressure and that the coolant evaporates and i need to replace it. Is it possible that i have a faulty coolant expansion tank? Thank you

[@sonoflight2758]

Why does it say on the manual not to add coolant if the expansion tank is empty. Air could enter the cooling system and damage the engine. What are the chances of that happening?

[@jeff13148]

I have a expansion tank with radiator cap you described 1st. The water level never changes whether hot or cold and engine temp is fine & no leaks. So I'm assuming there's no flow between radiator cap and the cooling system. I see the hose that goes from cap to the overflow tank and that doesn't seem to be a problem. I'm pretty sure the radiator is full. Any suggestions? Thank you for the video. Very helpful knowing what I have.

[@kevinhancock4064]

If its not overheating and you've got hot air I'd say dw . Unorss you feel something is wrong. I've personally got cause for concern lol (my car )

[@Motorman-dl1sc]

I have 2004 C5 Corvette no cool e leaks no dropping level in expansion tank but smell odor of coolen t after shutting car off hot top hose from expansion tank goes into radiator the cap says 15 psi now th does not sell 15 psi but 18 psi called th dealer 've said that is what it calls for is his a m flaw saying 15 psi Bettendorf o early so 18 psi looks like water pump had been changed and belt pulley rose color but not wet could the smell be the heat of technology belt burning off old coolent car not running hot 200 to 220 hot day in traffic any help On this

[@georgegrund6383]

My exspansion tank or so I think it because there is no radiatorcap on the radiator, will not pressurize at all but if I put the cap on it will throw out some antifreeze. I don't know what's going on? Plesae help. I tried to text it with a pressure gauge but it won't take any. I don't see a hole or a crack in it at all.