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855 big cam running hot ... DIRT culprit?

Discussion in 'Trucks' started by RenoHuskerDu, May 17, 2022.

  1. Truck Shop

    Truck Shop Senior Member

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    It would be a Horton 790000 series fan hub.
     
  2. RenoHuskerDu

    RenoHuskerDu Senior Member

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    Texas
    It's a classic thermal fan clutch. I have not heard it roaring yet.

    upload_2022-5-27_19-10-14.png
     
  3. Truck Shop

    Truck Shop Senior Member

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    A tired viscus hub. Viscus hubs were very common years back, many fleets bought/spec'ed with viscus
    fan hubs to cut costs. Probably original and probably shot.
     
    RenoHuskerDu likes this.
  4. RenoHuskerDu

    RenoHuskerDu Senior Member

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    We're familiar with that type of fan clutch. We'll give it a good check. Thanks for the tip.
     
  5. JPSouth

    JPSouth Well-Known Member

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    Dec 15, 2016
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    Location:
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    I have been fighting a similar overheating problem on the 8.3L Cummins in my '97 L8000. It only happens on warm days, pulling hard on passes, etc. Over time, I've been through and replaced a lot of components (water pump and thermostats needed done, anyway), the latest being the viscous clutch. The one that was on there appeared okay, passed a couple of the tests, but after a nervous two days finding a replacement, new one acts different - need to have a day with a hard pull to see for sure if it did any good. You pic looks a lot like my application, I hope you have better luck finding one, at least an inexpensive one. Parts stores and KitMaster were no help with the Cummins part #, which was 59921. Finally found one out in OR, (gulp) $475 ground shipped. Radiator is the final component, and same problem here .. nobody boils/rods the old ones out, gotta travel at least an hour to a shop elsewhere. A new, inferior, plastic/aluminum one in horizontal configuration is stratospheric in price.

    One hint, beg, borrow or buy the air hammer style clutch nut removal tool to take the thing off. I soaked the assembly point in PB for a day before attempting with a pry bar, air hammer/chisel and big crescent wrench - it did not go well. After a couple more attempts and some pretty inventive language, a buddy of mine who works at a shop loaned me his kit, 1 7/8" flange size fit, and it was off in 30 seconds. I'll never tackle that project again without one.
     
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