Serpentine Confusion

[JediKnight2]

I have a 2005 Explorer FlexFuel. I had to change out the alternator and bought a new belt. Alternator went on fine. The belt listed for my vehicle is 855K-6. However. .it's too big . The old belt on the vehicle is 850K-6. Anyone run into this before ? We tried to go up and down a year to see if it changed to the 850 but it didn't.

 

[TechGuru]

855 should be correct. Unless someone installed a smaller pulley on something most likely the belt tensioner is bad which RockAuto has a Motorcraft one for $29.79
https://www.rockauto.com/en/moreinfo.php?pk=3603762

BTW, I prefer to always use these Continental Elite (ex GatorBack) belts on everything I own...

https://www.rockauto.com/en/moreinfo.php?pk=1332875

 

[LoKo498]

855K6MK is the correct type!