94 D90 NAS w/ 60k miles. Previous owner said it started running hot late last summer.

Dealer said it needed a new radiator due to possible bad core. Did it. Problem continues. I have also replaced: thermostat, temp sender, and fan clutch as well.

Dealer also claimed to have run a pressure test to check the head gasket and said it was OK. There is no apparent coolant in the oil and the water pump appears to be circulating with no problem.

Truck runs only slightly hot while in motion. Idling for any period of time on a warm motor will cause temp to skyrocket. Infrared thermometer read around 230 when taken near thermostat housing on head.

Water pump? Head gasket? Exhaust constriction? Timing? ???

Any thoughts or suggestions?

Joe