Originally Posted by bugsandry
I will check on this tonight. So to summarize :
Fail open check : when car is cold and started, no coolant should be flowing
Fail closed check : when car is running normal, coolant should be flowing
if t-stat is stuck closed it overheats due to not opening and allowing the coolant to flow. t-stat is suppose to be closed on a cold start to make the car warm up quicker, then it slowly opens.
if t-stat is stuck open then the car will take forever to warm up. Once you start moving the car will run cooler.. however, in cars like ours with the absence of a gauge you may never know unless it is programmed to warn you. This is the safer of the 2 fails because it won't over heat.