Radiator cap not sealing.................................

[Drock]

I thought I'd share this elusive issue I experienced in case it can help someone else....... I'd bin driving around with blown head gaskets for about 6 months do to time & $$$ restraints. After finally installing a new set of aftermarket heads, Felpro gaskets, and ARP studs. The coolant system still wasn't recovering from the overflow tank? I assumed the worst, failed head gasket, or cracked block? As it turns out, the flange on the radiator, for the radiator cap, had mushroomed up. I guess from all the blow by of the head gasket leaks? I installed a new RAD cap thinking all the extra heat & pressure may have killed the cap, but still no change. It was only after parking the truck (up a hill) in such a way that the RAD cap was higher then the upper RAD hose so as to purge all the air from the system, that I stumbled upon the problem. By squeezing the upper RAD hose I could hear air escaping from around the cap, but ONLY AIR! The leak was soo small that it would only leak after cooling down, and not enough to let coolant out. The fix was simple, I just flattened out the outer edge of the mating surface of the flange with a body hammer so as to pull down on the cap more. Now the system works perfectly! I hope this helps if anyone having cooling system issues.. cheers