ive got a 93 gmc 4x4 with a new goodwrench tbi long block crate motor with maybe 10,000mi if not less on it and it has been losing coolant and overheating out of the blue. now everything in the cooling system is new i mean EVERYTHING and it doesnt miss or steam or has milky oil like a head gasket but my hoses are hard and my overflow tank fills up way past the fill level but wont siphon back sometimes. now ive got alot of money and time in this thing and i cant figure out for the life of me whats wrong and i know this is a camaro forum but ive seen some good tbi info on here so any info would be appreciated thanks guys

 

My first guess would be a bad or wrong style radiator cap.

 

i took the cap off last nite and topped it off and i checked it this morning and the radiator level went down half an inch

 

Did you leave the cap off or is the drop in level in the recovery tank? Was the motor hot or cold when you did this test? Is that a new cap?

 

the cap was off and the engine was cold and today i checked the radiator while it was hot/warm and it was full and the res tank went up like it should but i checked the radiator 10 mins ago and it was low like at the bottom of the tranny cooler. where could it be going? if the radiators low cold wouldnt it get lower when its hot and expands to the tank???

 

At this point I think you should pressure test the system or have someone pressure test it if you don't have the tools necessary to do so.

 

Run the engine with the radiator cap off and the heater on til the thermostat opens to check circulation and for any backpressure that may indicate a bad thermostat. incorrect intake manifold gaskets can cause air to be trapped in that area. You can also pull the spark plugs and turn the engine over to check for water in the cylinders. Do this after the engine cools enough to work on it but while there is still some pressure on the cooling system. That motor has a 3 yr 100,000 mile warranty on it if it is like the one I installed in my firebird last year.

 

if i were to pull it apart if it was a head gasket would that void my warrenty?

 

I don't know for sure, but I'd say yes. If you think it's a problem with the new engine, I'd have a professional look at it first and then contact the people you got it from before any disassembly, even by a professional shop.