So for about 2 years I drove around with a thermostat that was stuck closed and didn't realize it until recently. The engine never overheated. Temp gauge was always 1/3 of the way but my fan would constantly run. I thought it was a bad coolant switch or fan relay but it turned out to be the thermostat. So i bought an OEM thermostat and now i get fluctuating temps. With the car sitting at idle everything seems fine. Temp gauge goes to 1/3, fan turns on and off but with the car moving my gauge goes to 1/4. Is that normal? Shouldn't it constantly be at 1/3? I purged the air out of the coolant. any advice?

 

Did you bleed your coolant correctly? And did you test your OEM termostat before putting it in? It's always a good idea to test it before you put it in. Sounds like the thermostat is somehow stuck open.

 

I actually did test the thermostat before installing it. I purged it according to the manual but I can try again.

 

Are you 100 percent sure you installed it in correctly? Even with the pin on the upper side?

 

yup I'm sure. I wonder if it has to do with a new bumper I recently put on. Maybe it has more venting. The temp is fine while the car is not moving. Also I don't have AC if that makes a difference.

 

I highly doubt this has anything to do with your new bumper.. If the temp is fine while the car isn't moving, then the thermostat is stuck open. i recently had this problem but i was using a non oem thermostat and i switched to oem and it was good. Not sure why or how, but you have a defective thermostat.