99 Chevrolet Lumina overheating the thermostat was replace and the cooling system was drain and flush
There are lots of components to the cooling system - the radiator, hoses, cooling fans and the relays and switches that make them work, water pump, thermostat, water temp sensors and the heater core. Any one thing could make the car over heat as could a bad heat gasket or a dirty cooling system. I would flush the engine if you have not and check to see if the radiator is plugged up and if the cooling fans are coming on.
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