My car overheats when I’m driving at highway speeds for longer than 10 minutes. When I turn the heat on, the engine temperature drops. Some sources say to replace the thermostat and some say to flush the radiator. What should I do?
Have you checked your coolant level yet?
Both… after you check the coolant level as @pyrolord314 suggests. Also check to make sure the electric radiator fan is actually spinning.
The electric cooling fan is only needed when you are standing still, or barely moving. If you are overheating while driving at highway speeds, then that is not the problem.
I would first check to make sure that the radiator is full, that the thermostat opens when it reaches operating temperature, and that the coolant is actually circulating. A defective/weak water pump, or a radiator which is full of sludge could cause this.
If the coolant level is ok (in the radiator, not just the plastic bottle), and the coolant has been replaced in the last 3 years, my guess is the cooling system isn’t holding pressure properly. It might just need a new radiator cap. If the thermostat has never been replaced, now might be a good time to do it in any event. They usually start to distort a little by 10 years of use.
My radiator and reservoir are both full. My fan is working. I have even hearing across the radiator and my thermostat is working. I have heat and the heat exchanger helps me cool the engine. I have found that if I rev and hold the rpms at 3000, that will also lower the engine temperature.
I’m wondering if I need to flush my radiator.
Couldn’t hurt. If I had this problem on my Corolla I’d start w/a pressure test of the cooling system, and the radiator cap. Since increasing the engine rpm seems to help, next I’d check that the belt driving the water pump isn’t slipping, and then I’d remove the top hose to the radiator and verify I get a big flow of water out of that hose when the thermostat opens. If no big flow, I’d suspect either a clogged thermostat, or a faulty water pump.
Don’t forget to check the Engine Coolant Temperature sensor.