I learned the hard way not to ignore the coolant on my Eclipse V6 GT. Now after numerous flushes and cleanings I have, what I believe is a clean cooling system. When doing flushes the heater would work kinda sorta for a while. Now it seems to be losing coolant and engine oil, along with the heater problem. I bought a back flush kit and performed the procedure to excess. Refilled with coolant and Bars leak fix. Anything I'm missing? Oh yes the heat is better on the passenger side.

 

Blocked heater core. Bars leak does more harm than good sometimes. May cause a blockage and not allow coolant to properly circulate through the heater core

 

K Todd I realize bars leak can cause problems if not used properly. The problem is still little heat the heater core lines are, to quote my son, "pi$$" hot in and out. This is under the hood and under the dash. The radiator is new, Thermostat new, and the coolant is clean as a whistle. I checked the heat cool mix door the actuator is moving and you can hear the door operate. Oh I only used half strength on the bars leak.