There is very little to no heat in the SUV, it was that way all of last winter. The coolant over flow tank was replaced and the whole cooling system was flushed because the last owner tried to seal the crack in the over flow tank with some kind of goop that clogged the whole cooling system. The motor is now staying at a bit under 1/2 way on the temperature gauge with the air conditioner running on a very warm day, the A/C is pumping out very cold air even on a hot day. I have tested the heater and still little to no heat. I can hear the flappers under the dash panel moving when I move the controls. The heater core has been blowen out again. No change. I think the thermostat mite be bad. I came by this by trial and error. Am I on the right track?