I replaced my thermostat with a Carquest from Advanced auto in March after i started to get --- on the display and check engine light on. After the install I did notice the temperature gauge wasn't as high as it used to be. Temperature was stayed in between 160's-170's and hardly ever go over 180. 2 weeks ago the check engine light came on and --- appeared again. After a few hours I would drive again and the thermostat would come back on. Now its like every other day the temperature would only get 160 and then ---. I would go out for lunch break and temperature would come back on and be 175. Could it be another thermostat or sensor? or something else?

 

The answer is : yes, it could be the t-stat the sensor or something else.

The temp is supposed to be ABOVE 180F or the CEL will come on.

My guess is either the sensor or the wires to the sensor.

And welcome!
And I moved this to it's own thread.

 

Welcome to the site, replace the T-stat with the correct GM AC Delco T-stat, those others don't open to the ECM's liking and that is your reason for the code, unless the wires got messed up when you changed the Advance stat

 

Thanks, I will give that a try.

 

It corrected my issues , three years ago . I went cheap and learned the hard way!

 

I have found a very valuable tool for just such a problem. Harbor Freight sells a non-contact thermometer, just point and shoot. It will either confirm or repute your coolant temp reading. Use the thermometer to check wheel bearings or find out which cylinder isn't firing by shooting each header. Think your alternator is going bad...check bearing temps. Under $50.

 

A pyrometer won't open the T-stat on time to keep the ECM happy, but it will tell you how hot it is if pointed at the T-stat housing

 

Well after vacations and business trips I finally had the Thermostat replaced yesterday with an ACDelco Thermostat and Sensor. Yesterday the temperature was better and stayed between 180-190 and no issues. Then this morning it was very rainy and the Temperature would only get to 160 in the first 5 minutes then --- came back. The only thing else from when my buddy changed the last one was he drained, flushed and filled with the Green Antifreeze said the Dexcool causes to much gunk. Does green run cooler than the Orange?

 

Oh boy... You should always be using GM specific coolant for our HHRs or could risk damaging your cooling system.

 

Many after market t-stats have a faulty inner gasket. Or its not a 180F t-stat.

-- means it is not hot enough.