Chevrolet Repair: HELP!!!!!, head gasket problem, oil pressure loss

Question
hi i own a 99 camero. i recently took my cadallyic converter off because it needed to be guted and i couldnt find someone to weld it back to i had it cut off n a pipe added in its place. i drove my car 4 miles and it began to overheat. i pulled over and released some of the air that was in one of the lines under the hood. the guy told me it should have water coming out when you release the screw but i have alot of air. so when i release that the car cools until i began driving. now at times the temp guage will  go up then down. so when i was 4 miles from my home my vaulves started tapping. i went to pull over and my car shut off. smoke was coming from under the hood. i towed it home and the next day i started it. when it got ready to cut off it was loosing oil pressure. when i started it today it has great oil pressure. i do have a computer in my car. please help me and tell me what to do. i have a new thermostat and a new water pump and new coil packs. what else have a messed up? i was told my air flow censor may have gone bad? HELP ME!!!!

Answer
Hi Stephanie.... first i need to know what motor is in the car, from what you describe you have overheated the engine. If thats the case you may have a head gasket problem. install on the rad a pressure tester, see if car builds pressure in the rad really fast. if it does you have a head leaking compression into the cooling system. if rad builds pressure normal.(slowly) then gaskets should be ok...oil pressure loss could be as engine heats up oil gets thinner and if engine is running below normal operating RPM. Make sure that if you have installed new thermostat that you bleed cooling system completly any air in that system will cause poor cooling resulting in overheating and engine failure. hope this helps....