4 replies to this topic

[Oreo931]

Having a small issue with my fiance's 1997 850 GLT (107k miles).

I recently did a bunch of maintenance/stage 0, which included PCV replacement, coolant flush, new genuine volvo ECT (coolant temp sensor), and new genuine volvo thermostat.

The car runs great, no leaks or anything. A couple hundred miles after I replaced everything the car threw a CEL for P0116. I cleared the code and it hasn't come back for a couple of weeks now.

I was driving her car the other day and while sitting in traffic with the AC on I noticed the coolant temp gauge was sagging.(pointing to around 4 o'clock). About 10 minutes later after traffic cleared up and I was driving at speed the gauge returned to its normal running temperature position.


My only ideas are a defective ECT sensor (seems odd since this one was a brand new blue box part) or possible a bad fan relay.


Any ideas/input would be appreciated.

[r850glt]

Check the wiring from the sensor to the ECU, I had a similar problem and it would throw the car into limp mode.

[troyhyde]

Sounds like a bad thermostat. I've had a few problematic ones that I observed in a pot of hot / boiling water in the kitchen. They would kink a little to one side when opening and/or open too soon.

The reason I pulled them and studied them was some minor variation on the temp gauge similar to what you are observing. Between steady running and idle I would see small fluctuations in the needle.

[prasamin]

I would start by throwing the old ECT back in and seeing if the behavior changes....if not, then the thermostat would be the next issue....you sure you got the right therm? there were a couple of them available which have diff. temp ratings..


if you hear the fan coming on and off as it should, doubt the relay is bad.....

[Big Will]

I agree with Pras about the fan relay but it wouldn't matter what temperature thermostat you used (as long as it's reasonably close to stock). That wouldn't make the gauge fluctuate like that. Volvo stocks only the 90 degree ones now but I personally use an 87 degree in mine, other people use ones from 82 - 92. Either it's a defective thermostat that's sticking a bit or a bad ECT sensor.