I recently had an engine head change along with some other repairs and since then my water temperature indicator has been acting weird. Prior to repairs, if was fairly rock stable at about the midpoint on the normal temp range. Since repairs, it will sometimes go almost all the way to the red line and then quickly drop, and this is within about 100 yards of driving, to midpoint. I do not believe coolant/water can change temperature that fast. Would it be a sensor problem? Otherwise, the car is running fine and does not really seem to be running hot.

 

Thermostat is most likely bad.

 

Good guess! It was indeed the thermostat. It was rapidly increasing in the problem and I took my car into the dealership. Who knew it would be a $250 charge. I remember the days of picking up a cheap thermostat at the autoparts store and putting them in myself! Apparently, unrelated to the prior head work.

 

I have put in new thermostats and a week later they fail,fun x2.