What is the average operating temperature for an '89 240 with automatic,? My temperature gauge has never worked since I got the car, but there is a 52mm temp gauge where the small clock would have gone. When I am driving, it reads around 180, when I stop, in florida weather with no a/c, it will raise past 190. I pretty sure it bypasses the comp board. I'm just curious if these temps are normal, and what temp rating should a new thermostat be?

I just changed the oil last week (10w 40 mann filter, or should I be running 15w 40 with the weather averaging 90F lately?) and I will flush the transmission soon ( I'm not sure when the last flush was) and I flushed the radiator at the end of last summer.