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.
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