2001 Mitsubishi Eclipse • 127,000 miles

The heat blows cold air except for driving on the highway. As soon as I get off the highway it goes back to cold air. I then noticed a small puddle under the passenger side of the engine. The overflow was empty so I replaced some of the fluid. The fans are turning on and no visible leaks to any hoses. Yesterday I had a friend install a new thermostate and flush/bleed the radiator. He said the radiator should be getting hot and it's not. I picked up the car today and it still does not have heat and the temperature gage will rise to hot and then level out several times while driving. I noticed antifreeze coming out the front of the car once I got home. Not a lot and the overflow was still full. Any ideas?
November 29, 2012.

U will need to rent a pressure tester. It goes where the cap is. Then u need to pump it up. Then u can find the leak.

Nov 30, 2012.
You do need to pressurize the system to find the leak first, after that you need to bleed the system of air, you may have a restricion in the heater core or even a head gasket issue. But you have to fix the leak before you can go any further.

Dec 1, 2012.