It`s been leaking coolant at the waterpump . I put a new on there but i didnt wait a hr to put coolant back in it i pit the coolant in right after i put the new waterpump on. It has bubbles in the radiater and it overheat but when i turned the heat on ot doesnt overheat but now if i stop at a stoplight it overhests and when i start going again it still overheats what could it be?