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

tjsea · Oct 13, 2017

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.

chris142 · Oct 13, 2017

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.

ALBERT73 · Oct 17, 2017

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.

Dieselcrawler · Oct 17, 2017

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

03wr250f · Oct 22, 2017

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

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

80w90 or 85w140

80w90

85w140

Synthetic

tjsea

Full Access Member

chris142

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ALBERT73

Registered User

Dieselcrawler

Professional wrench holder

03wr250f

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