yoramw

My 944 turbo which has been very reliable so far developed a rather strange behaviour.
shortly after it reach operating temp and thermostat opens up and the fans kick in, it will overflow significant amount of coolant.

Water level is fine before it happens
II can feel the hoses getting warm once thermostat opens up.
I open the bolt at the top of the head to release air (I route the water back to the reservoir tank with and adaptor connected to a hose to release air.
At some point after much air bubbles clear up, I get the reservoir overflowing again...
No oil in water and no signs of water in oil.
I checked compression and though it is not perfect, it seems reasonable 142-147 across all 4 cylinders.


Before this happened, I did a few things that might have changed reliability:
installed standalone (VEMS, ran fine for a few months),
Installed Tial 38 WG(had the vacuum routed wrong initially, so first test drive did get boost higher than it should, but only one time for a few seconds before I realised it was over-boosting).
Installed an oil catch can.

My initial thoughts were that I have blown the HG, but none of the signs I expected showed up.
What would you recommend as troubleshooting steps?

Tom M'Guinn

I'd pressure test the cooling system to rule out external leaks. When coolant gets out, air gets in and replaces it, and when air gets hot, it expands and pushes coolant out the overflow. If the system holds 15psi for a good 5 - 10 minutes, yet seems to develop air in the system and overflow repeatedly, despite venting it, then I'd start looking more closely at the possibility of a head gasket leak. In the link in my sig line below, see the head gasket write-up, which starts with tried and true tests for leaking head gaskets.

p.s., also make sure the reservoir cap is good!

Good luck!

mj951

Excellent write-ups! Bookmarked.