I have a 1999 Mitsubishi Eclipse GS that i recently bought and has had several heating issues. It would start heating up after about 20 minutes of driving. My first thoughts were it is was either the thermostat or it was low on coolant. I checked the top and bottom hoses from the radiator and found no cracks, as well as the radiator. After flushing the radiator and changing the thermostat the issue seemed to be fixed, but after taking it out on a speed test drive it started overheating again. I was running the heater at the time and had to make about 5 to 6 stops to let it cool down to get the vehicle home. I did not let it go above 3/4 of the way up, but it did start smoking a little. After getting home I checked and saw that the reservoir was empty and there was no pressure on the hose going from the thermostat to the radiator. I let the car cool down over night and the next morning i started filling the radiator with 50/50 coolant mix and heard liquid hitting the ground. I looked under the vehicle and saw the coolant leaking from the back of the engine pretty fast. I am pretty handy with tools and would like to know what the issue is so that i can try to fix it. thanks.

 

sounds like a bad heater or bypass hose is bad