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Coolant system over pressurising on long trips

M

MK7 Mepa

New member
Location
Leicester
Car(s)
Golf MK7 2.0 TDI
Hi,

New here but I've got quite literally the exact same issue. 2014 MK7 2.0 TDI.

Expels the same way as you've shown in your pic after a long journey. Again with all tests done on heater matrix, egr, head gasket etc.

The only other thing I'm trying is to only fill the coolant half way on cold. It seems a huge pressure dump is causing the coolant to overflow so hopefully with it only halfway there's more then enough room for expansion.

If you find any other potential fixes please post on here, I've just bought the car so definitely a p*ss take.
 
tmw2442

tmw2442

Autocross Newbie
Location
Approved NPC storage contanier
Car(s)
Mk7 R
Sounds like the system isn't pressurizing at all, which in turn is causing it to boil over. Find a shop to put a pressure tester on the expansion tank, pressurize the system...if it holds, then you have a bad expansion tank cap, replace it...with the system pressurised if there is a leak...a mechanic should be able to find it.
 
tmw2442

tmw2442

Autocross Newbie
Location
Approved NPC storage contanier
Car(s)
Mk7 R
Chris_Golf7 said:
The other thing that was suggested is that it is the turbo-creating pressure back in the cooling system through the manifold. Not sure if that would be possible?
Click to expand...
Sounds like a miscommunication of what they are saying....or they are dumb; get a second opinion...
 
C

Chris_Golf7

New member
Location
Australia
Car(s)
2014 Volkswagen Golf
I am much closer to working out what the issue is.

I took the car for a long drive today - I used an OBDeleven scanner to monitor the coolant temperature at the engine outlet.

While the car was moving this mostly sat around 90-91 degrees but after working the vehicle very hard and idling the temperature would climb up.

It moved from 90 degrees to 100 degrees in the space of 2-3 minutes. The radiator fan did not come on to cool the temperature back down.

I started to take the coolant cap off and it started to overflow under pressure.

If I turn on the cold air conditioning then the radiator fan would come on and the temperature drops back down to 90 within 30 seconds.

My theory is that the radiator fan is not turning which is causing the coolant to heat up and expand out the top of the exhaustion tank.

I am wondering what temperature sensor activates the radiator fan and at what temperature it should cut in?

When the OBDeleven scanner was showing 100 degrees the temperature gauge on the car was still at 90 degrees too.

There was no fault code recorded for the radiator fan as far as I can see.

Any help is much appreciated
 
tmw2442

tmw2442

Autocross Newbie
Location
Approved NPC storage contanier
Car(s)
Mk7 R
You understand that unpressurized coolant will boil at 100, by unscrewing the cap and releasing pressure, it's going to boil over...it is being under pressure that raises the boiling point to around 120-125 degrees. Water at mt Everest boils at 70. A completely untuned mk7 the radiator fans do not come on without the AC being on, until around 105 ish. A car's cooling system needs 0.5 to 1 Bar of pressure to function.

The gauge in the car is normalized for the normie driver...it's going to show center at 90 until the car thinks its starting to overheat around 108-110 ish, then it will move.

So anywhere between 75-108 ish, the gauge on the dash wont move (it's programed that way on purpose),shows at 90. The gauge is normalized and not a real gauge.

zero pressure in the cooling system by starting to take off the cap and the coolant being at 100 = boiling...
 
Last edited:
F

FJBGTD

New member
Location
Southampton UK
Car(s)
Golf MK7 GTD
From memory my rad fan came on at around 102 - 106c when I was monitoring with OBDEleven. I had your issue and it was the heater matrix, the electric coolant pump flow was restricted when there was a partial blockage, which lead to limited coolant flow through the EGR cooler, which in turn lead to the coolant coming out of the coolant tank. My heater worked, also both flow and return pipes to the matrix were hot, it was just not as as hot as it should have been when the heater was on. When I removed the heater matrix and flushed water through it, it was very easy to tell that it was restricted. A new heater matrix cured the problem.
 
VDubberinDE

VDubberinDE

Go Kart Newbie
Location
Delaware
Car(s)
2018 VW Golf R
Just to confirm. You are not overfilling the expansion tank are you? I have seen people fill it all the way up, which is wrong. It's an expansion tank so it should only be filled to the line on the tank when Cold.
 
Jose_Gti

Jose_Gti

Autocross Newbie
Location
Philadelphia
Check the fuses. You can use this https://fuseandrelay.com/volkswagen/golf7.html
Find the radiator fan fuse or relay and apply 12v power directly to see if it runs.
If under power the radiator fan works then it could be the coolant sensor.
 
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