Tell me more ×  My Pontiac Montana is blowing warm air with the
heater turned on. I was receiving a code(not sure what the
number was but the message referred the engine was running
cooler than it was supposed to.) Since it never got over 140, I
thought it was a stuck thermostat. Replaced it with a 195
thermostat. Now it gets up to 180, cools and goes back to 140.
The heater heats up after it opens but cools down quickly after.
It only is hot for about 15 seconds, followed by 30 seconds of
lukewarm.  Ideas why the heater never heats up?  share|improve
this question add comment  1 Answer  I'd vote heater core issue
first. If the heater core is clogged you might not be getting
enough hot coolant through to get significant heat after the
coolant cools down to a normal temp.  The other option on some
cars is that the thermostat control itself isn't working
properly this would be more likely if the car has a digital
thermostat and the control is on the fritz.  share|improve this
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