2007 Chevrolet Equinox
Service department at dealership cannot find anything wrong!
Question = Intermittent problem - temperature gauge will show car is
overheating withing minutes of turning car on... Arm on gauge is all the
way up past the red overheat mark!!!  The fans are working, the water
in overflow tank is not boiling.  By time we drive to dealership, gauge
shows only slightly over half-way mark.  By time mechanic gets to it, it
is acting normal again.  Should we insist on a new temp sensor?
Answer: The thing with the temp sensor, you see, is that if it is faulty,
it would be faulty all the time. This is a difficult problem to try and
diagnose online. It might be best if you could leave the vehicle
overnight at the dealership, so when the mechanic looks at it, it
should act up upon starting. If there is an electrical problem, a trouble
code could be set in the computer. You could also have a problem
with the temp gauge itself. Since your engine seems to show no signs
of overheating, I would assume that it isn't and you have some other
issue causing your gauge to spike.