2002 Pontiac Grand Prix 40th Anniv GT, 227,000 miles. I have been running the 180 degree thermostat. Upon replacing the radiator hoses, I decided to reinstall the original oem 195 degree thermostat.
Now, the temperature gauge rises to a high temp of only 170 degrees or so. I removed the 195 degree thermostat and dunked it in boiling water, and it opens, then closes when removed from the water. So, I am convinced it is ok.
For now, I installed the 180 degree thermostat again, and all is well. The temperature gauge rises past 180 degrees and then settles back to where it always did before, and the heater throws much more heat.
I don't believe that there is anything wrong with the operation of the temperature gauge or the coolant temperature sensor.
Also, with the 195 thermostat in place, and the car idling in a warm garage, the temperature gauge still is not rising.
The PCM was programmed by ZZP, and the fans stay turned on after the engine is shut down. With the 195 thermostat installed, I regularly checking to see if the fans are running non-stop, and they are not.
I can't figure why this is happening. Upon searching on here for "thermostats", "temperature gauge", "coolant temperature sensor", etc, there is a claim that the operation of the cooling fans is the same with a 180 or 195 degree thermostat since difference is only 15 degrees.
I want to run the 195 degree stat to get more heat in the interior of the car.
What are other things I could look at?
