Clutch Fan Unscrewed Itself and Fell Off

[petersonj]

My brother-in-law moved his 2003 2500 4wd NV5600 truck yesterday. While he was moving it, I noticed a ticking sound coming from under the hood. Upon investigation we found the whole clutch fan assembly laying in the bottom of the radiator shroud. Not what I expected. The unit had unscrewed itself from the threaded pulley hub. The interesting part is that there is hardly any damage. The large clutch fan nut shows witness marks where the outside of the crank pulley was rubbing and two fan blades show similar wear from rubbing on the crank pulley hub. The fan blades never contacted the radiator or anything else (including the fan clutch thermal switch and wiring harness), which was amazing.

So, I am thinking that maybe the fan clutch was locked and the assembly came off when the engine was shut off; otherwise, I think the damage would have been much more severe.

Anybody ever had this happen to them? We replaced the fan hub bearing in December, 2018, just over 20,000 miles ago. I used the proper wrenches to remove and reinstall the fan clutch. Most of my life I was a mechanic by trade and I have been around Dodge trucks and many other similarly equipped vehicles and I have never witnessed or heard of this happening.

A new Mopar fan clutch and a new Dorman fan have been ordered.

- John

 

[Tuesdak]

By the way these thread on and off, yes, the fan can unthread itself when the engine stops. The constant torque from the air resistance helps keep it tight while the engine is running.

 

[petersonj]

@Tuesdak, are you saying that you have seen or heard of the happening?

 

[bcbender]

I think never "happening" would be hard to confirm as one would have to iterate and test to confirm it, but as mythbuster would say maybe plausible? It would have to be "really loose" and have several cycles of the perfect situation to unseat it,... Most never have this issue and it is designed (much like a string trimmer) to always be "treading on" in services so can it happen.. yeah maybe?.. But Id tq it down and move on with my time...

 

[Tuesdak]

@Tuesdak, are you saying that you have seen or heard of the happening?

No. The explanation helps helps when it's time to take it on/off.

Now I did hear about turning fans around on yellow iron for summer/winter with open cabs. Engine heat keeps the operator warm... Well one model uses the thrust of the fan to stay on. After two fans immediately came off at RPM $$$$ they quit turning them around on that job.