My friend and I have been trying to trouble shoot a problem with his 96 Z28 for a while now, and we don't know what else to look at. It's got a 355 w/ ported heads, cam, and a P1SC at about 10 psi. The problem is that it keeps losing coolant to somewhere and we cannot figure out where it is going. It is also getting a lot of air in the system to the point that it forces coolant into the reservoir until it blows the lid off the reservoir. It isn't related to to boost either because it does the same thing just tooling around town. We did a presure test for leaks in the system and found nothing. We suspected he might have a blown head gasket, even thought there are no signs of coolant in the oil or oil in the coolant, so we did a compression test and every cylinder was within 5 psi of one another. We tested the thermostat and it was fine. We flushed the cooling system and it still does it. Does anyone have any ideas what could be causing this or what else we can check? We are seriously out of ideas.

 

Yeah but a cranking compression test isn't the same as a leak down test. Cylinder pressure can still be leaking into the coolant system via the head gasket(s). To preform a leak down test you will need a steady supply of compressed air to enter through the spark plug hole, while that particular cylinder is TDC on the compression stroke (intake and exhaust valves closed). You should be able to hear air escaping into the coolant system, if there is a problem.

 

My roomate's car has the same exact symptoms... everyone seems to guess that it's a head gasket.

 

Was the cooling system bleeded properly?

When the coolant was bubling out of the resevior, was the engine overheating?

Did you installed in head studs and did you use lubricants or sealants. If you did not use good sealants for the studs, it will seep coolant from the water jacket below. I know

Small seepage will not make the oil milky. Another way to check is to send out the oil and have someone analyze it.

Good luck