Belt tensioner/ squilling....

[superDF350]

Towing out of Palm Springs into yucca valley when the fan would come on to cool the engine at 2500rpms you would hear the fan surge with a squill.
You let out of the pedal and it would go away. it sounds to me either the belt tensioner is going bad. it only does it whan i have a load and pulling a grade, and the fan kicks on. Pleasa give me some ideas. thanks

[Samuel1941]

Back in 2002 (or thereabouts) Ford changed the length of the serpentine (fan belt). Ford added about 1/2 inch to the length to make it easier to put on for the assembly line. The new longer belt had the same part number, so it was difficult to tell which was which.

Most noticeable on the 2002 I had when going at highway speeds and the air conditioner pump would kick on and momentarily stall the belt. Other times it would squeal when the fan clutch engaged the fan and again caused momentary belt stall.

This change caused the belt to slip on some trucks and make the squealing noise. Ford put out a TSB (technical service bulletin) and the fix was a new belt and idler pulley. This fix was done free under the 3 year, 36K mile warranty.

I don't have the TSB handy, so I don't know if this applies to you or not.
But, it sure sounds like belt stall.

[wkdjstr300]

I can post more specifics on it tomorrow, because I have the exact wording at work. But it is TSB 0718. I did it to my truck. It said something to the effect that in hot and dry conditions and when the engine is under a heavy load, the fan clutch belt will squeal.
Sometimes the fan clutch will rapidly cycle. The kit, which I bought from powerstrokeshop.com, costs less than $100.00 and includes a new belt, tensioner and WP pulley. Since I swapped it out, no problems. I can post the exact part numbers and everything in the morning...

[wkdjstr300]

OK, here it is...
2002/03 F-Sieries and Excursion belt squeal; 99-01 with replaced belts:
Some 7.3 engines may exhibit a loud squeal noise from the engine area when the engine is under load and the fan clutch is locked up, typically in hot and dusty conditions. Another complaint may be the fan clutch oscillating or not locking up. this may be due to dust accumulating on the back side of the belt and causing it to slip on the water pump pulley. This usually affects only 2002 model/year vehicles, but may occur in trucks built from 99-01 if the belt was replaced after July 01. On single rear wheel trucks, replace the serpentine belt with P/N 1C2Z-8620=NA on single alternator engines, and 1C2Z-3620-PA on dual alternators. Broadcast message 3848.
Also...A service kit has been released, it includes a belt, tensioner and water pump pulley. Use 2C3Z-8620-AA for single alternator and 2C3Z-8620-BA for dual alternators. Broadcast Message 0718.
As I said before, I bought the kit, 'cos my fan clutch was osciallting and I had the squeal. Since it was installed, no problems (knock on wood). I also replaced the upper radiator hose when I did this (and flushed the radiator). If you didn't already know, you can replace the upper hose with the hose for the dual alternator engine, same model year. That way you don't have to remove the upper hose to change the belt. I believe the part number for the hose on an 02 is F81Z-8260-CA.
Good luck:peace: :)

[superDF350]

Thank you very much for the info. Do you think just changing the belt will do it or should i change the wp pulley. Is this new part number for the belt a shorter belt to put more tension on the tensioner.. Thank again for the help.

[wkdjstr300]

From what I have read, the tensioners aren't the best and several have had success changing them out. If it was me, I would change the tensioner and the belt, keep the current belt as an emergency spare, behind the rear seat. That is, if you have never had the tensioner replaced before.
I understand the tensioners actually have more tension on them than the stock ones...FWIW