The simple question--Any longer term experience with retaining the 75-85 in the rear diff?

Longer version:
Hi all. I've lurked here thru the posts about diff fluid but do have a question. Have a new to me 2020 F250XL 6.2 gasser 4wd w/the sterling 10.5 open? diff (no electronic switch or anything on the dash) with 32,000 on the clock. Never used for any heavy towing by previous owner (I'm thinking a supervisors or somethings use truck for a company b/c the truck is in EXCELLENT shape but had many different profiles saved to the bluetooth). Anyways, I changed most fluids on purchase but the rear diff still has me asking questions. I changed it but went with Amsoil 75-85 per manual and Amsoils search result and the lubelocker gasket as recommended here. Most of trucks life will be a grocery getter and the bag of garbage to the dump, with about 10-15% of its life towing a roughly 10K pound tractor/brush hog/trailer setup. Any need to change that 75-85 out for something heavier (75/80-90, 75/80-110, 75-140) or is the 75-85 gtg for the long run. thanks to all in advance

p.s. Want to completely change out the power steering fluid too using the hose disconnect and lock to lock with engine off method.
Which of the hoses on the bottom of the reservoir is the supply and which is the return? thanks again

 

The lower weight fluids are to meet CAFE goal points .


ford only cares that your metal makes it thru warranty.

if you sell your vehicle before that then run the recommended sauce


if you plan to keep for the long haul…it makes sense to investigate what reduces wear .

 

thanks for the input speakerfritz. Sadly read about the CAFE stuff after changing it-was wondering why heavier had been the goto for decades and all of a sudden a change. Thoughts that 75-90 would make that large a difference? If not, then weight suggestion anyone? (since i prefer to keep vehicles till the wheels fall off). Forgot to mention I live coastal southeast so no extreme cold or anything.

 

When I changed my diff oil, I just used 75w90 full synthetic, much easier to find and much cheaper, no issues at all.

 

Ford has had the sterling 10.5 in use since 1983, running everything from 75w85 to 80w90 to 75w140 in it. I put 75w140 in my 2019 when I changed the rear diff, which is what I ran in my 2000 and 2002 F350s which had the same sterling 10.5 rear end. A 75w90 would work as well depending on use.

The magnet was pretty clean and the gears looked pretty good when I changed in but since I was going to be towing a 13k fifth wheel I went with the heavier top weight oil.

 

Thanks for sharing your experiences guys. I felt like I did lots of reading before changing it-should have done more 😂 Seems like the favored is 75-90 with the 140 being next. Maybe someone whose run and worked the 75-85 for while will chime in. Thanks again for sharing guys.

 

I believe Ford has switched the suggestion to 75W-140. That's what's going in my 105K mile F250. BUT, as you have recently changed your fluid, i would suggest running it as is until you really hook up to do some heavy towing. Unless you drag race your truck, in which case change it now.
The important take-home is the lighter oil isn't going to hurt your truck in normal use. AND, you picked a high quality lubricant. It's the heavy load situation where the heavier oil will give you better film strength. This axle is well-known and doesn't have reputation for trouble. Hundreds of thousands of them are in use and most people think very little about diff fluid changes. Where I grew up no one ever changed that fluid, but we lived in flat country.
R.

 

Same for me

 

thanks ATC, another input for 75-90-seems the most popular suggestion lol

 

Thanks dogdays. Running it for a little while is kind of what i was thinking since it is low milage truck, fresh fluid, and Amsoil. Since truck will be mostly a grocery getter and light towing (golf cart or a zero-turn mower) and only moderate weight as mentioned in OP when "heavy" towing, my thinking was/is that it should be ok; that said I'm not at all against spending a little extra in a different wight lube and doing it again with a more suitable weight if the benefit were that great. (I'm likely overthinking all of it as had a 97 f150 4.6 w/ the 3.55 back in the day that the pinion bearing and 1 of the axle? bearings-out by the rear wheel-went bad at ~150k miles, and fluid was changed out at ~90k (w/amsoil 75-140)... all that was a bear to R/R)

 

Same thing on the 3 valve engines. They ran 5w20 to meet CAFE and MPG requirements when they should've run 5w30 for the engine to last longer.

I always run 75w140 plus Ford's friction modifier, the only time I had to replace the guts in my differential was because they shimmed it incorrectly. It was actually a miracle it lasted the 12 years and hard miles it did.