Volvo: Thermostat for 850R, 850r, degree requirement

Question
Hi Jason,
I have an 850R 1996 that needs a new thermostat. It is running colder and the heater is cool. There are 2 different ranges, the 87 degree and the 90 degree. Any advice on which one is correct for this car would be appreciated.
Thanks,
Ralph

Answer
My general understanding is that you want the engine to operate with oil running at about 180 degrees F.  I'm assuming your temperature was in C, meaning the 87 thermostat will run at about 188 degrees F, and the 90 thermostat will run at 194.  My guess is that either one is fine; if it were my car I would want it to run as cool as possible once I made the 180 degree requirement.  Cooler temps mean less wear.  However, I'm not familiar enough with your car to know if it has any special requirements.  If you want to be absolutely sure you are getting the factory recommended one, I would give a quick call to the dealer, or look in a Hayne's manual for your model and year.  This isn't ultra critical though, neither thermostat will harm your engine.