1999 Chevy Cavalier – overheats to 260 degrees

Dear Doctor: My 1999 Chevy Cavalier overheats to 260 degrees sometimes when idling after it has warmed up. As soon as the car moves, the temperature returns to normal and stays normal at highway speeds. The cooling fan turns on at about 195 degrees. There is a slight change in the sound of the idling when the engine overheats. The system has been back-flushed. The thermostat and radiator have been replaced. There are no leaks of coolant or oil, and the fluids look fine. The antifreeze does not overflow and it stays at the same level. The car has plenty of power and is in great shape otherwise. The car has been driven for an hour at highway speeds with no problem, but later it may overheat after idling for several minutes. Could it be the EC-Module? Mike

Dear Mike: There are certain functions that need to be checked. First is the radiator flow rate. Just flushing a system does not mean the radiator can flow the coolant at idle. Next, check the water pump impeller. Is it worn? Then check the cylinder head and/or head gasket for failure. The cooling system needs to be checked with a gas analyzer or a special liquid for hydrocarbons in the cooling system. You need to check for air in the cooling system, too.

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