My car started to over heat, so I filled it up with coolant. I ran the car while I put some coolant in (till it was full). Then I filled the tank that's connected to it with coolant too. But its still overheating. I know it might be the thermostat but if it isn't. What else could be causing it too overheat when it ill filled up with coolant? The water pump runs on a belt and isn't leaking so that shouldn't be the problem I'm guessing. Any ideas?