2004 Chevrolet Silverado Intermittent heat

PSBOWLER

MEMBER
2004 CHEVROLET SILVERADO
5.3L
V8
4WD
AUTOMATIC
155,000 MILES

I have an interesting situation. The truck cabin warms up as the truck engine is warming up. When the engine gets to operating temperature, I no longer have any heat coming from the vents, just lukewarm air. I have had several suggestions from stuck thermostat to low coolant to old coolant clogging up the heater core. Only thing is, these would probably cause no heat at all, not the loss of it at operating temp. I was hoping someone here could point me to what could be causing my problem.

3 Replies

WRENCHTECH

MECHANIC
20,757 POSTS

With the engine at full operating temp, locate the 2 heater hoses where they go into the firewall and feel them to see if they are both hot to the touch. If they are both hot, the heat in that vehicle is controlled by a blend door that regulates heated air flow. It is operated by an electric motor/actuator. The problem can be that the actuator is stripped or inoperative or the door itself could be damaged. This is what needs to be determined by examining the actuator and see if it is responding to heat change commands or not.

If the hoses are not both hot, then we have an issue with either engine temp or coolant flow, depending whether it's one hose or two that is not hot.