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.

 

I don't know if it will fix your problem, but you need to bleed lt1 coolant systems, using the bleed screws to get rid of air , and air bubbles. You need to bleed the system if you have not. If you don't have the exact instructions, there are how to page links on here , or you can use the search to look for instructions, service manuals, or ask. If you already know how, try bleeding the system.