Car is running hot. Not actually in the red but above halfway where it normally runs and is pushing water out of overflow. Temp gauge moves up and down.driving 55 on highway and put into neutral. And

Asked by Nov 29, 2015 at 10:21 AM about the 1999 Pontiac Grand Am 4 Dr SE Sedan

Question type: Maintenance & Repair

Put car in neutral and coast the temp
gauge drops way down then as you
resume speed goes back up

3 Answers

14,075

If the water / fluid in the overflow, you're running too hot and it's harder on the engine.

77,905

Sounds like poor circulation in the radiator, when cooling demand is high like driving at sustained speeds the flow is restricted enough to show a higher than normal reading when you slow down or coast the heat demands go down and the radiator is able to cool the engine enough due to the lower demand. Check for restricted air flow through the radiator first, if you can see through the radiator fins then chances are high that it is plugged internally. HTH

25

Hi Jana, The situation you are describing is indicative of a temp sensor getting worn. Assuming you have checked to make sure the overflow is not overfilled and you are not experiencing any leaks, which will also cause this on occasion due to pressure problems. If overflow is good and your overflow cap is working properly then the gauge in your car works off of 2 sensors, one on the engine and one by the overflow. The sensor by the overflow is responsible for setting the 'serv. engine soon' light when there is too much water in the mix or if the overflow get too low, it also talks to the other sensor and the ECM calculates temperature differences. The temp sensor on the engine calculates temperature of the mix in the engine, when it gets worn it does not light the 'serv. engine soon" light until it fails and no longer completes the circuit to the ECM, unfortunately until it fully fails the worn condition cause what you are describing. It is very easy to change, as soon as you lift the hood it is on the right side of the engine and to the left side of the radiator hose. you unplug it and use a deep weel socket to unscrew it and screw in the new one. The gauge will start working properly as soon as the new one starts sending the proper signal to the ECM. Just a side note that I have been working on Grand Ams for almost 20 years and the engine in your situation is not really hot because if it were not the temp sensor this condition would blow the pressure cap on the overflow and you would see antifreeze on the ground by the passenger side wheel which is why I first stated about the overflow and no leaks. Good luck and God bless, get rid of the sensor before it dies all together. In short, change the temp sensor on your engine and you will be okay.

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