Mystery Pressure in coolant expansion tank

[Guest Xleon]

Hi,

 

Not been here for a while, but the vRS still continues to throw up new problems every couple of months (one of my most unreliable cars sadly, but it's such a good car to drive, I don't want to get rid of it, despite being 10 years old)!

 

I'm fighting with a coolant leak which I tracked down to the expansion tank.  It appeared to be leaking fluid out of the cap, most likely due to pressure build up.  The tank and cap have been replaced, there is no residue in the oil and no residue in the coolant. A sniff test has shown no gases in the coolant.

 

The temperature gauge never goes over 90, it's rock solid.  The fans are all working and cutting in/out correctly.

The thermostat has been replaced and the cooling system has been power-flushed.

 

The head gasket was replaced only 2 years ago, so it can't possibly be this!

EGR cooler was replaced a few years ago, so I'm also sure it's not this.

 

Has anyone heard of this issue or have any suggestions on things to try next?  I'm out of ideas now and I would really if possible, not want to get rid of the car yet :-)

 

Thanks.

[sepulchrave]

It's probably head lift, replace the head bolts with ARL bolts and see if that fixes it, if not you'll have to redo the head gasket.

[Breezy_Pete]

Is there positive pressure in the expansion tank after an overnight sit?

[hutchysrs50]

Yeah, i'd say headgasket again also. 

Sounds like your quite clued up really, most other options of what it could be have already been done, only thing you never said has been replaced is the water pump but if the temp gauge sits nicley then not likley to be at fault either.

Edited 23 June, 2016 by hutchysrs50

[Guest Xleon]

Thanks for all the responses.    

I am really hoping it's not a head gasket as it was done only recently, along with the cam-belt and water pump.

 

There is still pressure in the expansion tank after an over-night sit yes, but it only feels about the same as when the car was "healthy" but back then, I never kept opening it to top it up, so can't be sure :-)

 

So it's possible to build up pressure without the tell-tale signs of oil / residue / gases detected in the coolant?  I can't see what else it could be, but wanted to be sure.

It's so frustrating and sad to have this issue after only 96K miles and with it being well looked after.