intermittent heat?

[DFrank]

So my truck warms up fine and the heat kicks in normally, but 10-15 minutes of driving later the heat is barely warm. This is in steady city driving with +- 30 deg ambient.



Could this be a thermostat?



TIA, Dave

 

[rbattelle]

What is your coolant temperature when the heat output drops?

Ryan

 

[DFrank]

I guess it would read about 165 or so. Just the factory gauge that is supposed to make you feel everything is all right. The motor is warm enough to give heat, but the heat stops coming. I haven't done more than the daily commute recently to see if the problem goes away on the highway.

Dave

 

[Ducman82]

Coolent topped off?

 

[rbattelle]

I guess it would read about 165 or so. Just the factory gauge that is supposed to make you feel everything is all right.

The factory gauge is quite real, and is a reliable measure of the coolant temperature.



At idle, in temperatures below ~30°F, with the heater running the engine will cool down. Quite rapidly, depending on the heater fan setting and the ambient temperature. Sitting at a stop light my coolant can drop from 187°F to 173°F in only 1 minute with the heat on high and the outside air turned on.



At a coolant temperature of only ~165°F you're not going to feel as much heat. City driving doesn't generate much heat, so it's easy to do this. You might mitigate the problem a bit by turning on recirculation.



Ryan