How often do you change thermostat on 940, 1995? Also, coolant level drops

about 1" every 10 days. Is that normal (same car)?

 

Seldom, if ever..check the other post on radiators..Is the car running hot?
One way to check the thermostat is to put it in a pot of water on the stove and see what temperature it opens. However, by the time you go all the way to the store to get the new $3 seal to put the old thermostat back in, you might as well spring the extra ten bucks and get a new thermostat that comes with the seal.

 

Generally recommended to change the thermostat whenever changing the water pump. The coolant level should not drop 1/2" in 2 years.