I kinda figured that you have the 2.2L SOHC.
Then you will need to do one of the two steps. The cheapest will be to remove the thermostat from the engine, and perform a test on it. Just to make sure it is opening at the right temperature (195). The easiest way to do it is to boil the thermostat in water. Make sure that you have a thermometer handy and keep checking the water temp. The thermostat should start to open at about 190 and fully open at 195. Any other temp, the thermostat is faulty and should be replace, yes, again.
If the thermostat passes the test, then you need to perform other test. The instrument cluster. Unfortunately, you need to have access to a GM-approved scan tool to test the cluster. Here is the procedure.
Wednesday, March 25th, 2009 AT 9:27 PM