Diagnosing a Faulty Coolant Expansion Tank Radiator Cap

[@lakemphato9296]

The best video ever .........easy instructions ,demonstrations ...I solvef my cars problems aftet watching this

[@PBGarage]

Thanks!

[@youngindia7169]

Wow you saved my car I have a fiat punto diesel it has mysterious issue that no mechanic resolved, after couple hundred kms running car thermostat blown I replaced it Then after some days radiator blown and replaced new one After some days oil cooler started leaking Every time only coolant is leaking my mechanic said if you replace oil cooler also, then don't be shock if head gasket blown up. After researching google and KZbin I landed at your video and now I realized that coolant reservoir cap is not working properly. Good thing is car never overheated and didn't leaked too much coolant it leaks slowly and i did top up. Thank you very much.

[@PBGarage]

Glad we could help!

[@labi.not123]

I wanna thank you first of all for the amazing video

[@PBGarage]

Thank you too!

[@J4rn0]

Also bought an aftermarket cap which opens much higher psi, expecting it also causes problems. Went back to another oe cap i had. Tested them on similar type rigged setup. Thanks

[@PBGarage]

Glad it helped!

[@kinmin0]

different psi is the size and the thickness of the rubber o-ring under the cap. Worn o ring will release the pressure earlier. Over filled coolant always will damage the o-ring within few days and it become harden unable to hold the pressure, the coolant will boil and burst out or cause leak

[@drivertech3994]

İf can not hold the pressure , can i say the coolant liqud flow will drop and beacuse of that water can not reach to thermostat ? Or water can not circulate around everywhere at engine inside

[@PBGarage]

If it can’t hold the pressure you will lose coolant over time and you could get air in the system.

[@drivertech3994]

@@PBGarage thank you very much

[@mightymulatto3000]

The Audi rad cap valves are supposed to open at about 1.5 bar or 22psi on the 2.0L.

[@PBGarage]

Yep!

[@barrygreen9918]

Have you tried the 'shake test'? If you shake the cap in the vertical direction, are you noticing that the one you tested that chattered had a click/clack noise when shaken in your hand whereas the others have not? In engineering terms the clack is the sound of a higher valve movement which is giving a larger pressure drop, rather than a gentle slow bleed relief. Which inturn causes rapid coolant flash over in the hotest part of the engine! This week my Arteon has dropped the coolant level to Alert level (that is when the sensor wires in the bottle are no longer submerged), with a corresponding dash alert & ping "Check Coolant Level". This occured after 18 mile drive on two consecutive days despite topping off the level each time. I bought an OEM cap the third day and 30 miles 70mph testing the car was perfect an d no change in coolant level. Dash showed 90 C temp all the whole time. So then I took the orginal 25,000 mile 4.5 year VW cap for pressure testing by a non franchise garage. They reported it as fine, but opening at 28 psi (not 23 psi) and claimed it was therefore good to go. Then I watched your video today and I think it tells a story. By the way VW asked me to book in for a coolant check, but 2 weeks wait for a service booking, and the vehicle is required for TWO DAYS, to carry out full analysis before giving a price. What would that be on labour charges? Can I prove it is the cap?

[@PBGarage]

I haven’t, now I’m curious.

[@PBGarage]

That sucks about your Arteon. I hope they sort it out and it’s not a fortune.

[@mok822]

caps open at different pressure according to coolant system specification

[@PBGarage]

Correct, but seems some aftermarket caps are not correct for the 1.8 or 3.0 system.

[@garethhhhh]

When you weird cooling issues what do you mean? Just ordered a new cap because I've been having coolant going missing, not much but enough to where it needs topping up once a week. Came out an hour after parking up to look the other day and found the expansion tank backed up with coolant overflowing out the top. Would explain the missing coolant but im puzzled as to why it would overflow. Thanks.😊

[@PBGarage]

It burst one of the coolant supply hoses to the turbo, and it would leak coolant randomly from other places. If you have an AMB 1.8T, and you’re having that issue of the tank over-filling, or having issues with cabin heat, or the car intermittently overheating or blowing steam, you can try bleeding the air out of the system a few times but if it persists you may be dealing with a cracked cylinder head. VERY VERY common on specifically AMB engine code cars.

[@garethhhhh]

@PBGarage thanks for the auick reply. The heating is fine, and the car doesn't overheat. It blows white smoke for the first 10 to 15 mins of driving, but after that, it's normal again. It's a Peugeot 207, and I had the head gasket done 2 years ago. AA came around last week, took the cap off when it was hot, and it overflowed, so he had to quickly put the cap back on. He had to bleed the system to get the coolant to circulate again, but I have no visible splits or leaks coming from the system. I have no idea how the air rushed in, that's for sure when he took the cap off. Took it to a mates house, and he looked, couldn't see anything, and the system was circulating and behaving. Weird thing, though is it sometimes struggles to start, goes eventually, but then the Amber engine light comes on and the anti pollution fault (air to fuel ration I beleive that means) Thanks.

[@PBGarage]

@garethfox6352 that sounds like a cracked head or blown head gasket for sure. Combustion chamber pressure pushes air into the coolant system that’s why it keeps pushing out coolant or having air locks. As the engine cools down it pulls coolant into the cylinder and that’s why it’s hard to start and then runs rough and has a misfire on one cylinder until it pushes the coolant out and burns it off (white smoke). A couple tests you can do. Drive the car so it’s quite hot and park it overnight. In the morning, before you start it, pull the spark plugs and check for signs of coolant in the cylinders.

[@garethhhhh]

@PBGarage did think of checking the spark plugs. I've got one of those blue fluid mix things that you attach to the expansion tank to see if it turns yellow. I've a feeling it is the head gasket but still sit fingers crossed it isn't. Friend did say he thinks the water pump might be slightly leaking, so the air might be getting pulled in there. That's what I hope anyway lol.

[@PBGarage]

@garethfox6352 fingers crossed

[@balancereplays7722]

i have a vw vr6 gasoline engine.. when the engine is running and keeps heating the expansion tank gets almost overfilled by it self. car is not overheating stays at 90 Celcius fans works too.. what could be the problem?

[@PBGarage]

Sounds like it could be a leaking head gasket pushing air into the system.

[@balancereplays7722]

@@PBGarage so can i drive it or its a major problem that i must see

[@stevecharles2482]

Hi am currently having a problem with my car its over heating the reservoir is swollen the water pump beld has busrt and i replaced it it started work after it started to over heat wat causes that can i help me out

[@PBGarage]

If the car overheated before you fixed the water pump belt, you could have killed the thermostat or cracked the head, blown the head gasket. Lots of potential issues could have arisen.

[@Bruhvant]

Which caps would you recommend for the 3.0 systems??

[@PBGarage]

Rockauto sells Gates for $6, I’ve always liked their parts.

[@R3MILI]

@@PBGarageive audi A6 2.7 2007 which is the best cup

[@utbasat]

An amazing video, really thank you

[@PBGarage]

Thank you and you’re welcome!!

[@labi.not123]

My question is how do I know if the cab is doing his job if it’s opening when does it really open and release pressure

[@labi.not123]

The issue with my car is I feel like the cap it’s not opening I got a new one and I think the new one is still not opening when it’s supposed to because I feel like is getting build up pressure inside maybe at the Reservoir failed

[@PBGarage]

One way to find out is by testing it like in our video here.

[@PBGarage]

What makes you think it’s building too much pressure? Is it blowing off hoses? Or are you getting air in the system? Heater core stops working? Some of those could be indications of a blown head gasket or cracked head rather than an issue with the cap.

[@ColtonMFrey]

@@PBGarage I’m experiencing some weird issues. Air seems to be getting into my system, I can bleed it off but then after six hours of driving I can go bleed it again, rinse and repeat. I had some weird issues before, car seemed to be running a bit warm (not over half until shut down, then it would go just over half until it was turned on and coolant was flowing again, or it cooled) so I currently run a modified thermostat to allow a little extra flow and I changed out the rad, water pump and thermostat from before. No issues with overheating now but I am getting a bit of air in the system. Can a bad expansion cap cause this? Or am I looking at a head gasket? It can run for 12 hours without overheating, blowing hoses off (which it’s never done), or anything weird like that but after driving for a couple days I can start to hear a little water gurgle/bubble noise when I turn the car off which indicates air in the system, then I can bleed it again and get more air out. 2010 VW 2.5 Oil does and has looked good, no mixing anywhere and there’s no oil in the coolant.

[@labi.not123]

@@PBGarage thank you so much for replying! My issue is when idling the temperature going down on the engine and I lose heat in the car when I rev the engine everything goes back to normal. And the other thing is even wen the car is cold from over night if I open the coolant cap there is a lot of pressure and increases the coolant in the Reservoir.

[@magnat300]

what is the symptom with a bad cap?? maybe i have the same problem

[@PBGarage]

Coolant loss, air in system no heat in cabin, overheating, if the cap opens at too low pressure, coolant fittings, hoses blowing off, coolant leaks, swollen reservoir, if the cap opens at top high pressure.

[@stevecharles2482]

Nice question am having the same issue with my reservoir

[@blkcoupequattro]

Higher pressure cap will effectively lower the boiling temp of the coolant, but I believe my car Allroad has 2.7t engine has the lower pressure cap that opens at 21-22psi, racers use higher pressure caps to keep coolant from boiling, but that might also contribute to other cooling system problems with heater cores, radiators, hoses, etc....

[@PBGarage]

Yeah the car the high pressure cap was on had already suffered pressure related failures, coolant feed hose to the turbo burst, leaks from heater hoses, etc

[@chazwalker7156]

Hi, the water in my expansion bottle starts to bubble and come out of the expansion bottle overflow spout at around 100 degrees temp (also, the heater fails to warm up) we know it's definitely not a warped cylinder head issue. I've just discovered (when the engine is cold < before start up) that air passes through the expansion bottle overflow spout if I squeeze the radiator hose < is this a sure sign that the expansion bottle cap is at fault please?

[@PBGarage]

If the heater isn’t warming up you’ve got air in the system. You could try swapping the cap, bleeding the system really well, and then see where you end up. Squeezing a rad hose shouldn’t send coolant out the vent unless your tank is way overfilled.

[@PBGarage]

The overflow is under the tank, not the nipple facing the front of the motor.

[@PBGarage]

The heater core could also be clogged…

[@chazwalker7156]

Cheers for your replies. Sorry, I forgot to mention, the car in question is a (2008) 1.2 Vauxhall Corsa D. When I squeeze the radiator hose, when the engine is cold, air (not coolant, as it isn't over-filled) passes through the expansion bottle cap mechanism and out the overflow spout - I can hear the air passing and sucking through the spout as I squeeze and release the radiator hose. Shouldn't the expansion bottle cap machanism be closed (to allow pressure build-up) when the engine is cold and only open, for safety, if excessive pressure is created (because of a fault) within the cooling system?

[@paralelmind]

Hello! Any updates regarding opening at higher pressure long termn? Is there a problem if I go to a higher pressure coolant tank cap? For example the cap on my a4 b9 tfsi has 1.4 bar (blue cap) and want to change the whole coolant expansion tank with a new cap that has 1.6 bar release pressure (black cap). Both are OEM! Thank You!

[@PBGarage]

Well the cap that was opening at 26psi caused constant cooling system related issues, including blowing apart the coolant feed line to the turbo, and blowing apart the fill plug on the coolant pipe, as well as having leakage issues at the heater core connection. So who knows, might be fine, might not be. I replaced it with a cap that opened at the proper pressure and had no more issues.

[@paralelmind]

@@PBGarage thanks for the reply. The 1.6 bar is 23.2 psi.. It's strange that Audi changed the cap pressure with the newer coolant tank. :/

[@mukulrao1233]

I have a familiar problem like this, coolant reservoir talking overflow while driving car without switch on ac but if I switch on ac then everything works fine

[@PBGarage]

Sounds like it could be a problem with the radiator fan control. The fans turn on with the a/c but if the coolant temp sensor isn’t working properly maybe it’s overheating when the a/c isn’t on.

[@mukulrao1233]

Brother I have already clean my radiator, fully scane my car via scanner buy there is no fault. Also remove thermostat valve.. When i`m driving without ac on the radiator fan works slowly might be 10_20%. But in ac on its works on full speed.. Please help me out dude. What I could be.

[@PBGarage]

Yeah sounds like a problem with the fan control, the rad fans should be able to spin up to 100% if the car is overheating.

[@PBGarage]

Also check the readouts on both coolant temperature sensors.

[@rahulbisht5191]

Got any solution mukul?

[@TheyCallMeMannes]

I have a different problem. I just discovered today that the coolant level before starting the car was at MAX. Last time I drove was on Wednesday (hence "today" is Sunday"). I went for a 25ish km ride, and the coolant level rose up above the MAX line with the same amount as usual when in the middle between MIN and MAX. I parked the car at around 14h00 and checked the coolant level again at 18h00. it dropped just slightly below MAX level. the supercharger (It's an Audi S4 B8) was still quite warm. I'll check again tomorrow at 10h00 in the morning to see how much did the coolant level go down. I wonder whether it's safe to drive to the auto mechanic (about 15km of motorway driving or 15 min) or rather have the car towed there.

[@PBGarage]

As long as your temps stay normal then you should be fine driving it to the mechanic. Keep an eye on it as you're driving and if it starts to rise above normal, pull over immediately. Good luck!

[@Ape76]

There is no “max” level on any of them!?

[@jamesjones7183]

I wana put blue devil in my car is that the radiator and is that where you put the coolant or is the radiator cap somewhere else

[@PBGarage]

Yes that’s where you would add it but if you’re having coolant leaks, blown head gasket, or a cracked head, it won’t help.

[@jamesjones7183]

@@PBGarage my number 3 cylinder is only holding 60psi and I'm hoping it will fix it probably not gonna work tho right I'm a need a new engine

[@PBGarage]

If the engine code is AMB and you’re pushing air into the coolant then you probably have a cracked head. All you need to do is replace the cyl head not the whole motor.

[@jamesjones7183]

@@PBGarage okay can I ask one more question mg audi has 180,000 miles and number 3 cylinder is not holding compression right. So should I have my head rebuilt or the whole engine since it's so many miles and if I have my engine rebuilt will this solve the problem

[@R3MILI]

Two month ago while driving in highway i get the low coolant in my dashboard , i refill it with water without antifreeze and it again loose more then 300 gr in 30 km drive city . I send it to mechanic he told me that might have a leak in radiator , check it but nothing , after he told me that my fan dont worked after temp goes 92 celcius , he told me he fix it ,but again i keept loosing water the same , 1 week ago i sent it to another and i replace the cup and i add it for the first time antifreeze , i drive 30 km and in the morning i saw it the level was as it was filled , after i drive in mountain 20 km and again was ok , 3 days ago was for a drve in city no more then 15 min and when i seen in the morning it had less water but a very very little difference . Today i was in drive 80km and when i get home i let the car get cold for a hour i was the temp was 50 celcius , i seen the water was 3 mm down max and when i remove the cup it went to max . I dont know if this is ok , if the cup was the problem or it does has any problem again , please someone explain me

[@PBGarage]

Sounds like it could have been an issue with the cap but keep an eye on it. Does it start ok from cold? Any white smoke in the exhaust?

[@R3MILI]

@@PBGarage no nothing , everything its ok for start and no smoke

[@R3MILI]

@@PBGarage im doubting that maybe i put too much water and now the sistem has loose it to gat it to normal or not ?

[@PBGarage]

@R3MILI so I would wait and keep on eye on coolant level.

[@R3MILI]

@@PBGarage , just seen it , it lower than max , lower than it was . Might be maybe the cup has to be with bigger pression ? one more question, the mechanic only added 1 litrer of concentrate coolant , is it ok ?

[@1609dee]

Iooks like the one from Jenny's car is off the thread .it shouldnt be that hard to screw on

[@PBGarage]

Yeah it wasn’t great.