Low coolant temperature

santon

Registered Member
Original poster
Jun 3, 2020
35
Israel
I had relatively long journey (350 km, about 4.5 hours of driving) and suddenly noticed that my coolant temperature is low. The needle of the temperature gauge has moved a few marks to the left. I had my Android phone with the Torque application and the coolant temperature readings was about 73-75 degrees of Celsius. After 15-20 min of driving, the road conditions changed from a straight highway to the mountain road with curves and elevations, the load on the engine has increased and the temperature normalized (93-98 degrees C). After a few days, I had the same journey and the coolant temperature was completly normal. There were no SES light or error codes. Could it be an indicative of a bad thermostat?
 
Last edited:

Chickenhawk

Hobbyist
Dec 6, 2011
715
Bad thermostat or bad coolant temperature sensor. Hard to tell which sometimes, so you should change them both. It has been my experience that temps consistently low for weeks is thermostat, and temps that rise and fall on the highway are temp sensor.
 
OP
S

santon

Registered Member
Original poster
Jun 3, 2020
35
Israel
It could be that the stepper motor on your temperature gauge has begun to fail.
It is probably a bad thermostat. The stepper motors are new - I replaced them some time ago. Also, I don't rely on the gauge and monitor the coolant temperature on Torque application. I will replace the thermostat soon, already purchased a new one made by MotoRad, just need to find a time to change it.
 

Chickenhawk

Hobbyist
Dec 6, 2011
715
Change the sensor while you are there. It's not that much more work, as they are side-by-side. In my experience, your symptoms point more toward the sensor. When I had your same symptoms, I changed just the sensor first just so I could report back to this forum.

I was right, and didn't end up changing out the thermostat for another 4 years.
 

Mektek

Hobbyist
May 2, 2017
578
FL
I used to the Motorad thermostat too. Made in israel. I think it keeps a slightly lower temp than the OEM.
 

Mooseman

Master Blaster
Moderator
Dec 4, 2011
21,832
Ottawa, ON
I have found that the ACDelco controls the temps better. In my 02, I had used an aftermarket t-stat (I think it was a Stant) and found the temp was slightly to the left of 100c. I replaced that one with an ACDelco and was it was straight up. No actual temp readings as this was before I started using an ELM327.

Last one I installed was actually a Mahle/Clevite TI22688 which I found had the same type of crinkly bend in the tube as the ACDelco 1511006. Weird thing is I can't find neither on RA and there is no original GM part available neither.
 
OP
S

santon

Registered Member
Original poster
Jun 3, 2020
35
Israel
Yes, somebody told me that the Motorad thermostat has the lower opening temperature than the AC Delco. It was easier for me to get the Motorad here so I bought it. I will probably change the temperature sensor too. Surprisingly, I did not get any error code yet.
 

JerryIrons

Active Member
Dec 20, 2011
412
Just make sure you temp sensor is in fact accessible. On my 06 I6 ext, it's in a different spot, like at the back of the block near the firewall. I never did change it as a new thermostat fixed my problem years ago.
 

Mooseman

Master Blaster
Moderator
Dec 4, 2011
21,832
Ottawa, ON
If it's an 02-05, we recommend replacing the sensor at the same time as the thermostat since they are close to each other. However, 06-09 it was moved to the rear right of the head so it can be replaced separately if defective.
 

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