I recently changed my belts, hoses,thermostat, and changed the coolant on my 85 td. This was in preparation for an almost 700 mile road trip. The car ran at the proper temperature for the trip untill I was about 1 mile from dropping of Andy at his house. After pulling over and running the heater the temp came back down. I replaced the clutch fan thinking this was the problem. Two days ago I drove to Columbus (two hours away), no problem untill the return trip. The temp went up to about 110. I Ran the heater and it dropped back to 90, but then slowly went back up to 110. This was with the heater running full blast. It stayed at 110 for about twenty minutes and then returned back to 90. The weird thing is when I check under the hood when this is happening, the coolant in the reservoir is cold. Yesterday this happened on a short drive so today I swapped the radiator from another car that is running at the correct temperature and it made no differance. I replaced the new thermostat and it made no difference. This problem seems to have no pattern and has me stumped. I wonder is it possible that there is something floating around in the engine that restricts flow randomly?

The mileage is only 50k on this engine. The cam timing and IP timing are perfect. Valves are adjusted properly. When I start this one on a cold morning I never have to even touch the accelerator.

Sorry this went on so long. I needed to vent.