I have a 96 Silverado 2500, I am having problems with the heat output. The temperature will rise to about 230-240 with no heat output at idle, when driving the temp will drop to normal and I get heat. I've changed the thermostat twice with no help. I'm thinking the heater core may have blockage. What say you?

 

Sounds like it to me. More flow at operating speeds.

 

Robak, I need to ask a couple questions/clarifications.

Are you saying that when you let it just idle, that it runs up to 230-240° just on it's own. That's rather high, should stabilize at about 195°.

Do you feel "any" air (warm or otherwise) coming out the outlets just sitting there ? Or is there no air at all being moved into the Cabin unless you start moving/driving ?

 

I got it, Thanks to all for your input.

 

We're very glad you've resolved the problem, but...
One of the main objectives of this Forum, is the "exchange" of information.
Any chance you could post how your resolved it ?
It could be very helpful to someone who may experience the same problem.

 

It was the heater core, thanks for the help.

 

Thanks sincerely for the update !