(first - I am not a lawyer)

in the States, the Magnusson-Moss act basically says a manufacturer would need to prove you damaged a vehicle's system by doing maintenance outside of their network or using products not specified in the owner's manual. Yes, there could be some risk but, you aren't 'forced' to stick with Subaru trans fluid. It may be a rebranded fluid available aftermarket or there may be as good or better aftermarket choices. But, it could lead to some frustration if there was a failure and they refused to warranty it leading to some arbitration etc.

https://www.consumer.ftc.gov/articles/0138-auto-warranties-routine-maintenance

MAGNUSON MOSS WARRANTY ACT

 

Current Subaru gear oil is re-branded Mobil1 75W90, according to the parts guy at my local dealer.

 

Until I reach 100k miles, I have to stick with Subaru transmission fluid, but there seems to be no such restriction on the differential fluids.

no you don't.

Current Subaru gear oil is re-branded Mobil1 75W90, according to the parts guy at my local dealer.

Maybe at that particular dealer, but Idemitsu is the OEM supplier.

 

OEM Diff Fluid

Maybe at that particular dealer, but Idemitsu is the OEM supplier.

The factory fluid that came out of my diffs (and transmission) looked like conventional oil. I can't prove it and it could have just been age, but there was a (mild) cloudiness to it that I've never seen in used synthetic oils.

 

I have not personally used Redline diff fluid, but in other discussions on the same subject here, many have said they use Redline differential fluid. I have Mobil 1 in mine. I can't say that my fuel economy is any different, though.

 

I've used Redline diff oil and manual transmission oil in past BMWs with good results. Haven't gotten to diff oil replacement mileage on the Outback yet, but based on that experience I'll probably change to Redline then.

 

BMWs and Subarus



Ditto. Redline products got the driveline of my e46 to 235k miles before the car was totaled by a texting teenager. It also improved the notchiness of the shifts compared to BMW tranny fluid. I switched back and forth a couple of times before I decided Redline was definitively better and used Redline exclusively.

Based on that, I also started using Redline in the tranny and diffs of my Jeep, and got to 139k miles before that car was totaled.

Those experiences make me pretty confident in Redline products. I still have a gallon of Subaru ATF that I will use up, but then I will switch to Redline ATF. And as originally posted, I'm already using Redline in the diffs.

Redline's website specifies regular 75W90 gear oil in the diffs, but they do make a limited slip version with a friction modifier. For now, I'm going to assume their application guide is correct and not adopt that version.

 

Why 70w90?

I use Red Line 75w90, and so do many others on the front and rear Outback diffs. Great product.

I also use Red Line CVT fluid in the transmission.

 

Why 70w90?

I use Red Line 75w90, and so do many others on the front and rear Outback diffs. Great product.

Oops, my bad. I mistyped and meant to say 75W90.

 

I used Redline oil in my diffs, can't say I noticed any difference one way or another. I think the difference between new and old oil is much greater than between different new oils I used Redline as it's well regarded on here and wasn't that much more expensive than the standard stuff.

Now, if I had needed a couple of gallons of the stuff I would have looked elsewhere..

For the CVT I used the Subaru CVTII fluid as it was OEM and the same price as any other ($60 for 6qts). Definitely noticed a difference, especially going into reverse. I'm going to do another drain and refill this summer (~4000 miles later) then it should be good until 100k, with 60k on the clock right now.

 

When using any other fluid than that recommended by Subaru, make sure it meets both the GL5 & Older GL4 Spec, as many GL5 do not meet the GL4 Spec which involves protection for softer metals. (Some vehicles call for one and not the other, and the better synthetics usually conform to both specs, but not always). That said, I've always been partial to Royal Purple, which actually stopped a minor wet/seepage issue on my GMC Envoy's rear diff, and the Corvettes guys swear by the stuff.