2004 Dt466 overheating

What kind of fan clutch? If you have a viscus style, it needs to sense the heat from the rad to lock up. If the rad is dirty, then the air flow is cut off which causes over heat and no fan engagement. See if you have dirt buildup in between the cooling fins on the rad. We see dirty rads all the time and just need a good power washing.

 

If the clutch is in good shape, it should be very very stiff to turn by hand with the engine is NOT running and still cold. Once the engine runs for a bit, they usually become easier to turn as the fluid coupler inside disengages, then once your engine gets to around 215 or so it should re-engage that coupler and make the fan roar to life again. Never ever stick your hand into the fan when the engine is running to test it. Believe it or not, there are some Youtube videos of guys doing this!!!

 

Heavyd's assessment is spot on. Precisely why viscous fans are a bad idea on anything heavy duty. When you pull off to idle the clutch gets heat soaked and comes on due the lack of air flow through the rad. Once you take off again and load it up with no hot air on the clutch it never comes on. Nothing wrong with the clutch most likely. Your rad is blocked. Best to take it out for a thorough cleaning. It can be done in chassis but a much better job can be done apart.

 

If this is a pre EGR engine, check and make sure the coolant stand pipe is installed. Have seen them disappear once and a while and cause the overheat.

 

With refrigerant in the system you will need to have it recovered if you need to disconnect the lines for removal. Sometimes you can cheat and just swing it off to the side without disconnecting. Not sure if possible on this model or not.