Gear Oil at 20,000 miles in Ford 9.75” Diff

I would NOT change viscosity. And if you did, why 90? Why two steps, lower viscosity? Maybe, maybe think 110.

Anyway, the fluid definitely looks contaminated. Hazarding a guess it had some intrusion (water, dirt, wrong juice) at some point in the past and the simple drain didn't get it out. New fluid just picked it up.

Mixture doesn't bug me as a short, very short flush run. Might actually help as a flush.

Get better SOON. Just thinking about that feels painful!!
 
My 98 F150 Sterling 9.75 calls for 75-140, it is right on the metal tag attached by the diff cover bolts. I'm not aware that Sterling ever called for 75/80-90.
I had happened across that info a while back and didn’t bother to save it because it didn’t apply to my application. Since I tow, I’ll stick to the 75w-140 though. I wish I had a cool metal tag on my diff saying that. Heck, maybe I do but there’s that **** cross member right behind the cover, lol
 
I would NOT change viscosity. And if you did, why 90? Why two steps, lower viscosity? Maybe, maybe think 110.

Anyway, the fluid definitely looks contaminated. Hazarding a guess it had some intrusion (water, dirt, wrong juice) at some point in the past and the simple drain didn't get it out. New fluid just picked it up.

Mixture doesn't bug me as a short, very short flush run. Might actually help as a flush.

Get better SOON. Just thinking about that feels painful!!
Thanks Pablo! I agree with you, I think the SG definitely cleaned some gunk in there and ended up mixing it in. I still have that jar of old gear oil sitting on my desk and waiting to see if it will stratify any water to the top. Nothing yet, lol.

I appreciate it man! I’m doing pretty well all things considered. Replacing rear CV axles and all of the control arms in the rear of the Navigator this past weekend has me pretty dang sore 😆. I was feeling a little too good apparently, haha
 
Sorry bud, but as good as those are individually I’d never mix HPL & Amsoil.

Also, why are you using 75w140? 75w90 HPL is more than enough… it’s used in the #43 NASCAR’s semi differentials… the thicker fluid is going to run hotter than thinner fluid, and remove less heat. That can actually cause more issues than what you were hoping to avoid.
ya ford recommended 140 way back. My 87 f250 says to use 140.
 
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