Severity of overheating has been gradual. No signs of moisture on engine or in tail pipe. No oil in water or water in oil. It loses a tremendous amount of coolant within 3 miles. When idling the temperature gauge goes down. Guage goes up when driving. Also if I start the car and just let it idle for up to half an hour it will not overheat. The only place I see water after it overheats is near the overflow tank. Just a little. Turning the heater on doesn't cool it down but no heat is coming from the heater now. The heater worked when the problem started a couple of months ago. The car loses a lot of coolant within 2 1/2 miles. The car is obviously loosing fluid but other than a little at the top of the overflow tank can't see an obvious leak anywhere. The radiator has less than 5,000 miles on it. It also looks like there has been an overflow on the top of the radiator because stains are noticeable. Can someone please tell me what the problem might be? Thanks.