97 3.1 overheating DESPERATE

[Justinh722]

I have a 97 grand prix with 3.1 liter motor. Had a problem with the temp gauge going all the way up while accelerating on the highway. The coolant would bubble out the resevoir. The temp would go back down but as soon I accelerated again it would peg all the way hot. I decided to change the intake gaskets. Just got done replacing them and a bad FPR and started the car. The temp gauge didnt work at all so I went and tapped on the sensor and noticed it started working again. Has a new water pump, radiator cap, and thermostat. I bled the system at the bleed points. Tonight I drove the car and it pegged to hot again. Pulled over and didnt notice any coolant loss or signs of overheating.

I got back in and drove again and it pegged hot but then shortly after went back to the middle. I pulled away again and it stayed in the middle the whole time for the rest of the 2 miles home. When the temp rises, it does it very quickly as if its a shorted sensor. Is it possible the sensor is bad or is there a way to diagnose an overheating problem when it only shows signs during acceleration. Could I have a bad blockage in my coolant and in need of a flush? I used RTV and torqued all bolts to spec when changing the LIM gasket and upper.

[GTP Dad]

After reading your post I was going to suggest that you replace the sensor before doing anything else. Since you had to tap it once I believe that is your issue. The sensors are cheap and are not hard to replace. Make sure you use a good thread sealant, it also should be conductive to make sure that the sensor grounds properly. Sometimes teflon tape can cause issues.

[Justinh722]

Originally Posted by GTP Dad

After reading your post I was going to suggest that you replace the sensor before doing anything else. Since you had to tap it once I believe that is your issue. The sensors are cheap and are not hard to replace. Make sure you use a good thread sealant, it also should be conductive to make sure that the sensor grounds properly. Sometimes teflon tape can cause issues.

Sounds good. I'll give that a try first. I also don't think I properly burped the system when I filled it with coolant. I just filled it up and closed the radiator cap and opened the bleeders. I read that I should have kept the cap open and maybe should have had the car jacked up a little to relieve air bubbles. I also thought I heard gurgling from the heater core. Seems like this motor is a pain in the ass to get all the air out. I appreciate the help. Thanks

[GTP Dad]

Since you have a 97 open the radiator cap and start the car. Turn the heater all the way to hot and run the car. Watch the coolant level and when it drops add coolant. Continue to do this until the radiator is completely full. This will ensure that all the air is out of the system. Also don't forget to put some coolant in the reservoir as this will keep the system full. These are much simpler coolant systems to bleed than the newer ones. You may also want to change the radiator cap if it is not new. It may not be holding proper pressure.