Two days ago my heater stopped working. The next day, my car began stalling whenever I would slow down or stop. The RPMs would drop to the floor, then the engine would stall. It does not do this when it is cold. Today, I discovered that the radiator is leaking. The oil is not milky, and there does not appear to be oil in the radiator. Also, there's no cloud of white smoke when driving. Could the stalling be simply because of lack of coolant/overheating?