Hi all.

Been struggling with this one for awhile.

For the last few months, the temperaure gauge never reaches 3 o'clock. For twelve years, it's always been steady at 3. Car takes awhile to warm up and seems to be running cold. No CEL or codes present. Car runs fine; good gas mileage.

Assumed the t-stat was stuck open. Replaced it with a 90C Volvo t-stat...no change.

Recently, the cooling fan has been running after shutdown for about 3-5 minutes. Yesterday, turned the car to "ON" without starting it. Fan comes on (it's 50F outside).

Figured it was a bad fan relay. Replaced it...no change.

Any ideas? I haven't changed the engine coolant temperature sensor yet. Does the temp gauge get its data from the ECT?

2000 S70
Non Turbo
85,000 mi

 

I've been thinking I have the same problem lately. You're the first person I've come across who thinks it's there too.

 

Replaced the ECT sensor. That was the problem. The temp gauge quickly returned to 3 o'clock and held steady, the fan isn't running after shutdown on a cold engine.

One thing I thought odd...I never had any CEL code, but after replacing the ECT with one from Volvo I got "range error" (P0116). Reset the code and it hasn't re-appeared.

I can only guess that the ECM remembers the most recent value sent by the ECT. Upon changing the ECT, the ECM must have received a drastically different value (the correct one) and lit the CEL.

All is good now.