car over heating

No, the overflow tank has little to no effect on the engine cooling. If you turn on the heater that adds the heater coil to cooling system and will probably reduce the engine temperature some but is only a short term solution because the heat will be inside the car with you. It can help, however, if you are overheating and just trying to make it to a garage.

Another short term solution is to loosen the radiator cap which can help in the same situation where you are just trying to drive a few miles to get home or to a garage. Doing so releases the pressure in the system and can prevent the coolant from turning into steam.

You probably need a cooling system flush if you don't have any leaks.