80w-90 or 85w-140 Which and Why ???

Discussion in '6.9L IH & 7.3L IDI Diesels' started by MIDNIGHT RIDER, Oct 11, 2017.

80w90 or 85w140

  1. 80w90

    2 vote(s)
    16.7%
  2. 85w140

    5 vote(s)
    41.7%
  3. Synthetic

    5 vote(s)
    41.7%
  1. tjsea

    tjsea Full Access Member

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    I believe all of the 99 and up supeedutys with a 10.5 sterling come factory with 75w140 synthetic in them. Since it's basically the same rear as ours thats what I plan on running. I always liked Amsoil so that's what I'll be installing at some point this winter.
     
  2. chris142

    chris142 Full Access Member

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    Some aftermarket gear manufacturers say that Synthetic gear oil wont remove heat as well as dino oil. I find that hard to believe considering the amount of pickups and 18wheelers that come with syn from the factory.
     
  3. ALBERT73

    ALBERT73 Registered User

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    Not so many years ago Eatons warranty was 500,000 on 80w90and 1 million on Syn. must be a reason. They shipped new trucks with 80w90 run 12,000 miles then switch to Syn. dont think they do that anymore.
     
  4. Dieselcrawler

    Dieselcrawler i pooped today! Staff Member

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    all my buses at work (400+ in the company) came with 75-140 syn. this is international and chevy mini buses.
     
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  5. 03wr250f

    03wr250f Full Access Member

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    Spec on the 10.25 iirc is 85-140. Now reading in my textbooks from tech school there was a bar graph that struck me. 85-140w is good for lubrication down to -10* where 75-140 is good to -40. Also as previously stated 10.5 spec is 75-140. Since I get a good discount through our shop I will be switching to 75-140 over the 85-140 i previously ran. If you live in a place that comonly gets down around -10* I would go 75-140, otherwise I wouldnt sweat the difference between 75 & 85w
    and spec for front iirc is 80-90
     

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