Rear axle/diff fluid

[mattp321]

2017 limited 2.3 ecoboost 4wd.

Manual calls for "SAE 80W-90" fluid, Motorcraft # CXY-80W90-1L.

I think this is a conventional oil. Can I refill with the Mobil-1 75W-90 full synthetic instead?

Is the Amsoil 80W-90 (AGLPK-EA) full synthetic a better choice?

Reading some posts, seems some are filling Fords with 75W-140.

I've never done a diff fluid change so thanks for any advice.

 

[Odrapnew]

I believe there's a different thread on here about the different fluids.

When I changed my rear diff (2x so far), I used Amsoil 75W90 Severe Gear.

 

[CDW6212R]

I love the Severe Gear, it's the best and not the most expensive. I choose the weight by usage, severe duty you should use the 75W-140, but for light duty and a light footed driver, the 90 weight is good enough if it's synthetic gear oil. I stock all three of the Severe Gear weights for my Fords, I like the lighter two for the front diff, for my two AWD 302 Explorers. They went up last year though, it's about $15 a quart plus taxes now.

 

[mattp321]

Thanks guys. My Explorer definitely does not get "severe usage" - more like soccer mom/highway driving. Of course, if you judge by the number of times it's been back to the stealership for "repairs", you'd get the impression I'm driving it across the moon.

I tried to read some of the threads but I can't really make much sense of them and the true difference between 75 and 80. I mean to me that's only "5" different which doesn't seem like much but again I have no idea about this stuff.

I'll probably just mail order the Amsoil Severe Gear 80W-90 then, stick with the recommended spec but go full synthetic rather than the Ford Motorcraft. It's just that 80W-90 doesn't seem to be available locally, whereas 75W-90 is easily purchased at every auto parts store here.

 

[CDW6212R]

The real difference for gear oils is quality. The type is huge, synthetic is way better than the plain dino oil stuff parts stores sell. The brands matter too, Motorcraft is always a good baseline for quality, many who knows them brands should never be used. The Amsoil and Royal Purple are the best common known brands, others like Valvoline etc, are fine too if they are the synthetic versions.

The viscosity is mainly for usage, Ford changed their required specs for the rear diff, to the 140 weight in the late 90's. So for any 8.8 diff, that should be the best choice of weight. But then the highest quality gear oils(lower weight) will be fine if you are easy on parts, and fuel economy was a big deal for lots of highway driving(thus a 110 in the rear would be fine then).

 

[Mbrooks420]

75w90 will be fine. Just use a quality oil as mentioned.