OK. Here's the deal. I started my car this morning and ran it on fast idle for no more than two minutes with the sole intent on checking the coolant in the radiator. After shuting it off, I checked the fluid and it was fizzing!No, not boiling. It looked like Alka-Seltzer in my radiator, but it had the consistancy of the head on a freshly poured beer (which, by the way, sounds pretty good right now!). The coolant wasn't hot at all to the touch. I've already checked my spark plugs and everything looks fine. Compression tests find nothing wrong, so I know its not the head gasket. Is it possible that one of my heads is cracked? I don't know what else it could be. I've ruled out the radiator cap, external pressure differences, and I'm pretty sure its not the head gasket (unless the compression tests lied to me). BTW, 72 Chevelle 350/350TH 4bbl. factory air. PLEASE HELP!!!