View Full Version : Thermostats don't work while driving?

09-29-2010, 07:37 PM
My thermostat doesn't read the coolant temp until after the car has been stopped for several minutes. When it finally does read the temp it sits at the standard temp as indicated in the manual until I start driving a few miles, by which time the gauge has dropped all the way down. Also anytime I drive up a large hill the temp gauge starts working again. The car runs fine, I've never had any problems with it and the timing belt/water pump both were replaced 20k miles ago. Any ideas? :D

09-29-2010, 07:39 PM
Sounds like a bad coolant temp sensor (CTS). It's cheap and easy to change.

09-29-2010, 07:57 PM
Also sounds like a bad stuck open thermostat that what my car was doing changed the t stat wand good as new

09-29-2010, 08:10 PM
Okay sweet. Ill order one asap. Also had another question, not sure if these two things are related or not. But when I turn my heat on its not really hot, like its warmer then the air outside, its just not like blazing hot. So I don't really even bother using my heat. Any idea if these two things are related or why my heat is never very hot?

09-29-2010, 08:21 PM
when you change your t stat that should fix your heat problem. same thing happened to me ;)

09-29-2010, 08:40 PM
Sweet :D thanks for all the help guys.

09-29-2010, 09:00 PM
If your heat never gets hot then that's defiantly the thermostat its stuck open over cooling the car.

09-30-2010, 03:33 AM
Stuck open thermostat

09-30-2010, 04:17 AM
Stuck open thermostat


change the CTS anyway to be sure - make sure you get the old o-ring out and put a new one in - make sure the clip is fastened securely to avoid the sensor popping out.

09-30-2010, 11:54 AM
Here's a tip to find out for sure whether it's the t-stat or CTS, assuming you have climate control:

1. Turn off the A/C unit
2. Press the UP and RECYCLE button at the same time

You will see the temperature read 90 degrees or something like that.

3. Change the temp until it reads 51 degrees and press RECYCLE again.

You will see the temperature of the water as the ECU sees it. The CTS apparently only sends the temperature to the cabin - the ECU reads the temperature from somewhere else. So, if the climate reads 90 degrees and the instrument cluster says something else, your t-stat is fine - it's your CTS. You could also try this trick from a cold start and see if it gradually raises to 90 degrees.

Oh and depending on the year of car, sometimes you need to tap into 49, not 51 (apparently).

09-30-2010, 07:35 PM
Lousy heat and low temp reading on the dash point to t-stat. I'm officially "changing my guess" after this new info on the heat was added....Officially.

10-03-2010, 11:17 PM
Well I've tried everything suggested and still nothing is working. Same problems. I know the CTS and t-stat are both correctly installed. Any more ideas?