have changed thermostats twice in 05 diesel but heater warms up then temperature drops and lose heat in cab
2005 2500hd diesel. thought thermostats were bad. will blow coolant out the overflow when left sitting idle for a little while to. the gauge inside will go up and ill have heat but then drop to nothing and the heat quits working
it could be a sludge build up in the matrix for the heater try back flushing the system
the other fault could be an expensive one as the head gasket may have begun to go if that is the case you will have to get the head planed and an over size head gasket but dont go for the stainless one with rubber inserts as they are crap if you can go for a copper one and torque the head down 3 to 5 pounds over the setting and that should solve the fault
You could also have a collapsed hose, a worn water pump, a blocked radiator, bad head gaskets, and who kows what else. In any case you need to have a mechanic look into this before spending more money on guessing what could be wrong. Even the radiator cap may be bad and not keeping the correct pressure. By the way, why do diesel owners keep their motors idling when not in use? I notice this practice and it just seems so wasteful, regardless of the amount/time involved. Anyway, good luck withe vehicle.
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