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Cooling system / head gasket issue?

kojolaing

New Member
Joined
Jun 5, 2025
Messages
1
Location
London
Car
C200 CDI Estate
Hi everyone

I have a 2012 W204 with the 2.2 OM651 engine (C200 CDI)

This car had so many issues when I got it, and I have done a lot of work myself.
- Oil cooler (coolant tank was FULL of oil) - oil cooler and fuel filter housing replaced
- Coolant tank itself was not holding any pressure - new one fitted
- New thermostat fitted

Since this work has been done, I have had numerous coolant pipes replaced, they seem to build up a lot of pressure and burst.

Thought I had dealt with the last of the coolant leaks, but after a long day of driving in stop start traffic (no coolant warnings) - I left the car overnight and in the morning the dreaded message returned - low coolant. However with a totally cool engine, when I tried opening the header tank, a lot of pressure was released and it spewed out coolant. I let the pressure out after losing about half a litre of coolant, let the engine run from cold with the top off the header tank, the level dropped a fair bit, and I topped up again and closed the tank. I've driven it for about a day and a half since and no coolant message yet but I'm now beginning to get a dreaded feeling that there is a slight leak from the head gasket, which is slowly building pressure in the cooling system.

Why else would there be pressure still in the cooling system after sitting overnight?

Temp gauge never goes above 80

There is no sign of contaminated oil, dipstick and oil cap are clean. No more oil in coolant tank either

Is there anything else that could cause this? I am happy to do any work myself but if it's the head gasket then I can't do that on my drive!

Car has done 180K miles...

Any help is much appreciated!
 

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