Q: How hot does my thermostat run?

A: Stock thermostats on 3rd generation cars are 195 degrees. If you want to go colder, you must change the PROM. This is due to the computer having preset temperatures to determine warmup and fan start conditions. A new PROM in conjunction with a thermostat change will allow the car to maintain a cooler temperature by moving the fan start temperature down to within the range of the new thermostat. In addition, most PROM upgrades will lower the warmup temparature so that the computer will not think that the engine is constantly in warm-up (enrichment) mode. Changing the thermostat without changing the PROM can lead to drivability problem and less-than-expected results, but this varys with the application.


Is this true for a 91 firebird if I wanted to install a 180 degree thermostat?

 

I don't personally recommend colder stats, however a 180 should not pose any real problem. With average stop and go driving your engine temp will be generally higher than 180 anyway. Unless your driving is all high speed you should not really have any driveability issues.