The temperature gauge in my 1996 Mazda 626 has been dead for as long as I have had the car (years). I never bothered to fix it because the car seemed fine. I recently had an issue where I discovered a crack in my radiator when steam started billowing from the hood. An accurate temperature gauge would have been helpful in that situation.
I recently replaced the radiator myself. Now I'm interested in addressing the temperature gauge. Considering the temperature gauge has been broken long before I had a problem, I assume that the gauge is faulty and not the cooling system thermostat (though I haven't tested the thermostat).
What's involved in testing/fixing the gauge?