1999 interior Heater in GMC 6.5 diesel

robbor · January 10, 2017

I have a 1999 GMC sierra diesel thats an old state truck so its really just like a 1998 K2500.

Anyways my interior heater doesnt seem to put out the heat in the interior that it should.

It does not have any sort of actuated valve in the engine compartment to route the heat the the interior heater core like alot of the gas engines do.

Any ideas what to check or how it works? I cant imagine it would always be routing heat to the core even during the summer when you have the ac on.

azblacksheep · January 10, 2017

Im not sure what youre talking about when you say actuator.. theres 1 hose that goes to the heater core from the radiator and one will go to the motor. Theres no actuator under the hood, on a gasser at least, and im sure your oil burner is the same. Check on the passenger side firewall for those 2 hoses. If they just loop thru then the core is probably leaking so the hoses were re routed to delete it. If they connect where they should and one hose is hotter than the other, the core is plugged.

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