Q: My car is still overheating after I replaced the thermostat

Let’s focus in on the fact higher RPMs have an effect on your engine’s cooling system. There is only one main component in the cooling system related to engine speed and that is your water pump. The pump is powered by the drive belt which runs at the same speed as your engine. The water pump pushes the coolant through the engine, and cycles it through the radiator where a majority of the heat transfer (or cooling of the hot coolant) takes place.

The coolant is run through areas in the engine block where it picks up the heat from the combustion happening inside. From there the hot coolant is run through the radiator where its temperature is decreased, and then its ready to pick up more heat from the engine. If the coolant is not cycling through the engine, the cooling system will not work. The water pump can fail, as well as the pulley that drives it. I recommend further inspection of the coolant leak by a professional mechanic at this point.