[ET160]

I replaced my thermostat about six months ago.


Yesterday, I found my temperature gauge drifting down as I picked up speed on the highway. I assume the thermostat has failed in the open position.


On the other hand, I'm surprised, given the interval. Could I have a bad coolant temperature sensor?

 

[andybisnut]

I replaced my thermostat about six months ago.


Yesterday, I found my temperature gauge drifting down as I picked up speed on the highway. I assume the thermostat has failed in the open position.


On the other hand, I'm surprised, given the interval. Could I have a bad coolant temperature sensor?

Could be either. Most of us on here replace both (sensor and thermostat) when we do the job, since parts are cheap. Sensor requires a deep 19mm socket if I recall. It's super easy to swap especially if you already have the coolant drained.

This is one of those weird situations where OEM is really important. The first time I did the job, I used aftermarket parts and still had gauge issues when I was done. Had to do it a second time, this time using both the OEM thermostat and OEM temperature sensor.

 

[ET160]

Thanks for the tip. I'll replace both parts.

 

[EdT]

I replaced my thermostat about six months ago.

Yesterday, I found my temperature gauge drifting down as I picked up speed on the highway. I assume the thermostat has failed in the open position.

On the other hand, I'm surprised, given the interval. Could I have a bad coolant temperature sensor?

I have installed two Saab OEM thermostats, and both have worked perfectly--even when I use Tech II to tighten the band in which the gauge stays horizonal. It always stays horizontal.


On the other hand, I installed an OEM equivalent Motorad thermostat (Saab is the only fitment for this model) and the gauge would droop as you describe.


Oddly, the Saab OEM thermostat was made my Motorad. However it had some detail differences, and it didn't do that.


I have only changed one temp sensor, and that was because it was bad (the pigtail broke off). A sensor would read consistently off, but if it goes to horizontal and stays there if you let the car idle, then it's probably reading correctly.


TL;DR: get Saab OEM thermostat (good luck, hope Orio hasn't repackaged something from Proparts :nono, install, and see if you still have problems.

 

[MI-Roger]

I replaced a bad sensor on my '08 a couple years back. The gage would drop to zero while driving down the road, then come back to the 9 o'clock position.

I borrowed a Cummins Old-Style Diesel Valve Adjusting Wrench from a neighbor which allowed me to do this job without draining the coolant or removing anything in the engine compartment.

Dang it was cold the night I did this!