Originally Posted by
Cerberus
*fair warning, i'm bored and halfway picking on your diagnostic process, don't take it personally*
1. you seem fixated on thermostat failure.. which is certainly possible but not the best way to diagnose a problem. diagnosis requires that you not jump to conclusions and then substantiate them, but rather consider all the possibilities based on the known symptoms then narrow your focus progressively eliminating possible problems as you go.
2, true but incomplete. a thermostat that only opens partially would only be likely to overheat in warmer weather where the temperature differential is less able to dissipate the engine heat. In normal/cool weather, overheating would be very unlikely.
3. This one is a lot harder to agree with. first of all, a thermostat rarely sticks in a partially open state. some may fail in that they don't close right, but then go wide open when hot, but i've never seen one fail the way you describe.
again, not trying to be a dick, just bored.