Thermostat

[capt jack]

Quick question. Should I replace the thermostat in my 97 S90 (3 litre 204 bhp) with a new 87, 90 or 92 degree stat?

Various sites seem to recommend various options with no real consistency.

Or does it not really matter?

My reason for changing the stat is that I’ve noticed lately that the heater output seems to vary a bit, a little cooler at speed, hotter in traffic. The temp gauge sits in the middle.

There are no coolant leaks anywhere.

Thanks

Cheers

Jack

[Forrest]

Personally, I would replace the thermostat with one the same rating as I took out unless it is fairly obviously wrong or causing a problem. I think Volvo varied them according to regional climate. I doubt the few degrees variation will make any significant difference under most normal road driving conditions.

[aardvarkash10]

usually the thermostat is matched to the radiator fan switch sensor.

If you are changing the rating of the thermostat you should change the fan sensor as well.

Within limits, warmer is better from a performance/economy pov.

[Dippydog]

Handbook for my '95 MkII 960[which I believe is same engine?] says 87 for the thermostat.How much-if any- difference a warmer thermostat would make I don't know.

[Laird Scooby]

Go for the 92C Jack, along the lines of what Ash said, you'll almost certainly find the fan is controlled by the engine management ECU so should auto adjust to the new 'stat once it relises it's warming up to a slightly warmer preset point.

You'll benefit from a faster warm up, better heater and imprved engine efficiency which means performance and/or economy, depending on your right hoof.