Schaeffers 75w-90 in a Ford Sterling 10.5?

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Sep 12, 2022
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Hello everyone, I have a 2017 Ford F250 Powerstroke with the Sterling 10.5” 3:31 e-lock rear, with just about 60,000mi, I would say a good 75% of the miles are towing, either a fifth wheel camper, skid steer and car trailer, or a snowmobile trailer.
Looking in the owners manual I see it calls for a 75w-85 synthetic, would anybody be scared of using a 75w-90 in this case? I use a lot of Schaeffers products in my vehicles, have always seemed to have good luck with them, currently running their OTR Plus 5w-40 in the engine.
I’d really like to use Schaeffers or the High Perf Lubricants I’ve been reading about on here, but am a little nervous with it calling for such an odd spec, was actually surprised when I seen the lower grade in the owners manual for a Super Duty, my last truck was a F-150 and it called for 75w-140 in the rear!🤷🏼‍♂️
I also noticed looking up a previous gen 2011 Super Duty with a Sterling 10.5” it does call for a 75w-140 as well, what do you think changed? The E-Lock?

Thanks in Advance!!
 
I would not run 75W-90 in it. I would use 75W-140 because I would opine the reduction has everything to do with Ford chasing CAFE credits (MPG). I would want the extra protection of the heavier viscosity.
 
The Sterling 9.75 in my 98 F150 calls for 75-140...JMHO, but if I were towing heavy like you are, that is what I would be running in the rear.
 
I ran 75W- 140 in the wifes 2002 Supeduty and still run it in the wifes 2018 Superduty. The p/u is used to tow the the wife and daughters horses around, plus other stuff. My 2015 F150 gets 75w-140 as well. Both pick ups E loc s work with the 75W-140.
 
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I don't use my F-350 in the winter much, but it calls for 75w-140 in the 10.5. I think it's been proven multiple times that thicker gear oil runs way hotter. If I did use it a lot in the winter, I'd run a 75w-90 in it.

Mine has 4.10 gears so the pinion is going to be spinning a bit faster. But 1/4 of the torque as your PSD.

I know 18 wheelers usually call for 80w90 in the differentials.
 
I don't use my F-350 in the winter much, but it calls for 75w-140 in the 10.5. I think it's been proven multiple times that thicker gear oil runs way hotter. If I did use it a lot in the winter, I'd run a 75w-90 in it.

Mine has 4.10 gears so the pinion is going to be spinning a bit faster. But 1/4 of the torque as your PSD.

I know 18 wheelers usually call for 80w90 in the differentials.
Define "way hotter". I have never seen an increase in heat between 75W-90 and 75W-140 in any axle I have had or experience with.

Both oils have a winter rating of 75 so that part is irrelevant for this topic and OTR axles are apples and oranges against light duty axles.
 
If grocery getter, 75w-90 for the quarter or half a mile to the gallon. If ever highway or loaded, or trailering you need 75w-140.
 
Gain a 1/4 or 1/2 MPG by reducing the viscosity in the rear axle?
In the winter.....absolutely!

Years ago I drove such a short distance to and from work, and to lunch and back all the oils were still like grease. When I drained it in the winter, I removed the rear diff cover and the fluid was frozen in place. Had to scoop all the factory fill out and then place a large torpedo heater to get the fluid to come out.
 
In the winter.....absolutely!

Years ago I drove such a short distance to and from work, and to lunch and back all the oils were still like grease. When I drained it in the winter, I removed the rear diff cover and the fluid was frozen in place. Had to scoop all the factory fill out and then place a large torpedo heater to get the fluid to come out.
Must have not been a synthetic oil because a 75W-xx would not result in any loss of MPG and would pour out all way down to a seriously negative number below zero...
 
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