the temp gauge doesnt have much to do with the theromostat, its the sending unit... That temperature gauge is extremely sensitive, so if it doesnt move, something isnt plugged in correctly, or the sending unit has failed... You would know if your thermostat is bad because the engine will either run to cold, or to hot... And FYI its normal for that gauge to read pretty high before the radiator fan kicks on, its got a fiarly low temperature setting which makes it look like its running to hot, but really its at normal operating tempreture.
