1999 Grand Am - Sensor/Needle in red danger zone - wait 5 minutes - then it is fine - mechanic finds nothing

Question

ok have more space to type. I am driving along, minding my own business, and then hear a ding, look down my temp gauge is lit up red, needle as far as it goes hot, and the indicator basically is telling me my car has overheated. It drives fine, not rough, I pull over immediately. I sit for about 5 minutes, restart my car, it says it is hot, but going to pull over to a safer area, but once I get going, needle goes back toward 200, and then car drives just fine. I take it to the mechanic and it won't overheat for him. This happens every now and then, but never for the mechanic. He has replace all the coolant stuff except for the radiator, he checks the fluid, etc. Good mechanic, knows what he is doing, has over 20 years experience, but this is weird. Any ideas? We were thinking maybe computer problem, he used the heat sensor, not hot, but of course it had already cooled of by the time I get the car there.

Answer 1

If you are talking about your heat/temperature sensor being in the red for 5 minutes then dropping down into normal I would say that it is probably fine.  What is happening is your thermestate has to heat up to a certain point before it will spring open and allow water to enter your engines cooling system.  When your gauge returns to normal is when the water enters.  If the gauge is constantly doing going into the red and back this would indicate that you have a low water level in your radiator.  I would put more in there.  There should be a reservoir under the hood (I think to the bottom left looking from the front to the back.) that has a line in it that says "hot."  If water is up to that line while your car is running then that is the appropriate amount to have and none needs to be added.  If the gauge just does this one time (about 5 - 10 min after you start driving) I would call this normal and not worry about it.  I hope this has been helpful.  If you require more assistance I would give more details about your problem.

Answer 2

If you would edit your post and provide more details we might be able to help you.