I have an 89 d250 with the 5.2L. I started having overheating issues a few weeks ago and attempted to deal with the simple and inexpensive fixes first. Here's what I've done so far; replace thermostat (195 degree), installed new water pump and 4 new belts. I've done basic diagnostics on the fan clutch and do not think that is the issue, but I'm not 100% sure. After install of new water pump, drove truck about three miles-down 1.5 and back up a fairly steep grade and it was boiling in the overflow tank. I plan to flush the radiator today (I know should have done that already), but I would appreciate any other thoughts about what else to check. Thanks. Japhy

 

Any white smoke out the exhaust? Coolant in oil? How old is the radiator? Every used any stop-leak on it?

 

HeyYou, Thanks for the response and the answers to your questions are: No white smoke and no coolant in oil. I've had the truck for a little over a year so I'm not sure about the last few questions, but knowing the previous owner a bit, I think that the radiator has not been replaced (if it has it would have been before he owned it which would have been 10+ years ago. I doubt it has had any stop leak in it.

 

Might wanna yank it, and have it professionally boiled out. Could just be full of sediment.

Either that, or just replace it with a new one...

 

If the clutch is good you will hear a roar from the fan when you first start it up. Rev the motor to about 1500 rpm's that will be fast enough to hear it. Also take it out on the highway at 50+, You will have enough air flow through the radiator to cool it. If it still over heats it's probably the radiator.