Coolant boiling over in expansion tank

AWX BAKES

MEMBER
2015 VOLKSWAGEN GOLF
2.0L
4 CYL
2WD
MANUAL
85,000 MILES

Hi,

I have the car listed above gtd. Issue is that I have a coolant leak. It seems to be coming from the expansion tank. Only happens when the car is been driven hard. No leak at all from normal driving. When I pull up after a harder drive there is evidence of the coolant boiling out of the expansion tank. The water temperature gauge one dash still reads 90 though and doesn’t show signs of over heating. I’ve just had the water pump and cam belt changed and also a new expansion tank. The garage where I got this done don’t seem to be able to diagnose the issue or have made no attempt to. Just hoped the water bottle change and cam belt would fix the issue.
I’m looking for some advise on where to point them next.

Thanks,
Alex

3 Replies

ASEMASTER6371

MECHANIC
52,797 POSTS

Good afternoon,

I would change the thermostat. It may not be opening fully or on time causing the fluid to boil. I know the thermostat is part of the coolant pump. Did they offer any option for temperature?

https://www.2carpros.com/articles/how-an-engine-thermostat-works

https://www.2carpros.com/articles/replace-thermostat

The other possibility is the head gasket may be leaking and causing the fluid to boil under load.

https://www.2carpros.com/articles/head-gasket-blown-test

Roy

Image (Click to make bigger)

SPONSORED LINKS

Was this

answer

helpful?

Yes

No

Tuesday, October 6th, 2020 AT 10:46 AM

AWX BAKES

MEMBER
2 POSTS

Hi.

It has been back in today for a full diagnosis. They cannot find any issues with the head gasket or any other checks they can do with pressure testing or temperature testing.
They only thing that they maybe believe is that there maybe some sort of failure in the charge cooler that is forcing pressure back into the expansion tank that only happens when the engine is under load, ie I’m driving faster.
They plan to get it on the rolling road tomorrow and try replicate the scenario as to when the tank either over boils or gets under too much pressure. They then can nip off the pipes to the charge cooler to see if this stops the flow of pressure.
I kind of makes sense?

Thanks for you help.

Alex

Was this

answer

helpful?

Yes

No

Wednesday, October 7th, 2020 AT 9:50 AM

ASEMASTER6371