I have a 07 dodge caliber sxt- the heater started blowing warm air a year after we got it-then the next year cold. I changed both (it has 2) thermostats and it wennt back luke warm for 2 months then cold. we had a tech look at it and say the heater core was bad, 600$ to fix, i said bull-not leaking in the floor. after he drained and refilled the coolant though, it was warm for a couple days then went cold. I took it to the dealer, they kept it 5 days, said it would only reach 180 degrees, must be thermostat stuck open- i advised they are new- they eventually changed them anyway, said there was also a possible gasket problem letting air in,
- called me and said it was warm, includung the engine operating temp, i went to pick it up, 320$- my wife got in it 3 hours after they called to say it worked, drove it home.........ya- no heat and it never warmed past it's usuall temp a bit over half way between cold and warm.. around 180 degrees.
Soooooo... what the @%$@#???????
the computer says the Blend doors are ok- although 1 time we did seem to have heat out of a couple vents only for about 2 days, thats why i asked them if there was a blend door issue.