Overheating and Intake?

01 Grand Prix, 130,000, just had the upper intake replaced by a friend who owns a shop. The car was overheating and losing coolant. The plenum was worn out on one of the intake holes. He did a compression check with all cylinders coming in at he says 3100 psi. I have already replaced the tst, water pump and radiator. Also, has new ac delco plugs and wires. Well today it overheated on me again and this time I lost some power somewhere. When on the gas it just didnt have the normal pickup. The car has a misfire at idle, but is smooth when on the gas. I just got the car back yesterday and paid them for there work and now it's broke again so this would really suck If I blew a head or something which it sounds like I did.

Thanks for any reply...

Chris in Houston

Take the car back as they obviously didn't fix the issue. Make sure you got all the air out of the system and that the radiator is not blocked. Also check the cat as it could have been damaged by water from the first issue. This can cause a loss of power. Do a compression check as the 3100 PSI your friend quoted is way off base. Make sure he uses the correct guage this time.

is this a GT with the 3.8 or an SE with the 3.1?

GM issued an extended warranty on all 01-02 W-bodies (including your Grand Prix) to 7 years/120,000 miles due to a known issue with the converter breaking apart and clogging itself. A simple vacuum test would determine if the converter is blocked. This will also cause overheating and loss of power due to the exhaust gasses not being able to escape.

Your fans might not be coming on....which blows air through the radiator and condensor to cool the water in the radiator before it circulates through the engine block. I dont think you have a blown head Gasket, check for Coolent in your oil, and mabey take a plug out and see if its all funky, cause if you got a head gasket leak, you'll be getting oil into your combustion chamber possibly.

Guys,

Thanks for all the replies. I misheard him when he mentioned the psi for the compression check. The guy who has been working on my car is ASE certified and used to work for GM so this guy def knows what he's talking about. Unfortunately, I hit about 126k when I found out about the cat so that def sucked. We looked at the car over the weekend again and this time we def have water in the oil along with an antifreeze smell of white smoke from the exhaust. Broken head gasket? I think so. Time to rebuild thanks to the upper intake issue. Thanks GM for great parts!

Car is an 01 GT 3.8 NS, good engines just crapy plastic parts to go with it.