So how major is this going to be???

[hemihead]

Just started up a fresh rebuild on a 454 on Fri night. Engine has been sitting for about 3 yrs. New main bearings pistons, cam, oil pump, timing set intake, carb, HEI, Etc.

Started and ran well, really responsive the whole time.

Had trouble keeping the engine temp down at anything above idle, tried running it at about 2000rpm for break in but in about 3 min the temp gauge would creep up to the high mark. First time we thought we had air locked the cooling system (bottom hose was cool). Pulled rad cap and way we went, saw lots of air coming through so ran motor with out cap for a while. seemed to be okay, replaced rad cap and increased rpm, temp increased again. let cool down and tried again with rad cap off, again more air bubbles, reved motor seemed to get worse, finally ended up with a hot cooling system and steam puff through rad cap hole. FYI using a aluminum rad.

Our thoughts were possibly a bad thermostat but top hose was hot, pulled thermostat and is in correect position.

Other suggestions thoughts were exhaust gases getting into water jacket via blown intake gasket or head gasket or cracked head.

Oil stayed clean and no moisture out the tail pipes during the run.

Before i begin ripping doeas any one else have a diagnoses??