Mitsubishi Eclipse Climate Control Problems

in Mitsubishi
For the past 3 winter seasons, my heater blows cold air when stopped at a traffic light/stop light. It's a 2001 Eclipse GT. I took it to the dealership 3 time while it was still under warrenty and they said that there was nothing they could do. They said it was the way it was made! Oh well, how ridiculous is that. The problem did not exist the first year or two. The defrost ONLY BLOWS cold air while parked and idling. I can leave it running for 30 minutes with frost on the windshield and it will not even get warm. As soon as I start driving.....boom.....it heats up. Any one have any knowledge of what could be wrong?
0
Comments
Today I spent a rainy afternoon day to run the car with cap off and heater and fan full blast for 2 hours thinking air in the system. (Possible heatercore or water pump leak) I started the car with heater and fan full blast to remove air and added coolant as needed. Car ran for 2 hours once system seemed to be filled and cycled through turning off fan to turning off heater and so on. Also, reving engine every 20 minutes. I noticed some inconsistencies in the coolant resevoir while this was going on. While heater fan off, the fan on the rad would turn on and suck about 1 inch of coolant out of the resevoir. Shutting off heater would cause coolant to rise above "full" level in resevoir.
Finally shut off vehicle and let cool down. After an 11/2 hours, I took vehicle for ride. Shortly after a mile with heater temp on warm, the temp gauge began to rise again!!! I turned on the heater fan to high to diffuse but to no avail. I pulled over and popped hood to see resevoir filled with coolant and began to puke about a pint of fluid. (This has happened before)I again cycled thru high heat w/ fan, no fan and no heater at all. It almost seemed as if thermostat failed to open, but is brand new!!.
I am wondering if ANYONE has an answer to this mystery that causes me to drink!!!
Thanks
Ed B