Possibly a faulty coolant pump.
thermostat
VENT TO HEATER CORE IS NOT CLOSING................
You are in the beginning throws of blend door failure. Check www.heatertreater.net for more information on diagnosing and fixing the problem.
This frequently happens when the heater coil is going bad.
Heater core changed three years ago,I changed Thermostat Heater still blows cool air.
can you please clarify what you mean, do you mean that the front heater blows cold but the rear blows hot or do you mean that when the heating is on cold it blows hot? many thanks paul
If the coolant level is okay, I would suspect a restricted heater core. Try flushing the heater core.
the heater blows warm air when fan is on low but blows cold air when fan is turn to higher setting
The heater fan ONLY blows the air, it does not make the temperature of that air. Your heater temperature controls how hot the air is. Adjust your heater temperature for hotter or cooler air.
Get the air out of your heater core.
we changed radaitor & thermastate , now heater blows cold air
most likely your heater-core went bad. if you car runs perfectly fine besides having heat. if you car gets up to normal temperatures, doesn't over heat. the fan blows, but just blows cold air. then it is the heater core.