Join Date: Sep 2007
Location: Louisville, KY
Car Year: 2008
Car Model: LL Bean (4EAT)
I just changed the differential oils on my 2008 AT with 13,000 miles. I had collected various posts on how to do it, and noted these items of interest:
1. It was not particularly hard to break loose the rear diff plugs. They don't have gaskets, but wedge themselves, so I put a little Hylomar blue gel sealant on the threads. It does not get hard, but will stop seepage.
2. The front diff plug uses a hard thick solid copper gasket. I had bought a $3 new one, but the old one was perfect and could have been reused.
3. Although both diffs use the same gear oil, the rear oil was watery and gray, while the front oil was still light amber and viscous. The rear plug magnet also had a thick coating of black ferrous fuzz, while the front magnet had only a light coating.
4. I replaced the OEM dino oil with Redline synthetic 75W90 GL5 gear oil. This has got to be a "must" for the rear differential, which quickly destroys dino oil. I also wish I had done this much sooner. Subaru really ought to require this as part of the first 7500-mile service.
5. The previous posts said buy 3 quarts because the rear diff takes almost 1 quart and the front diff takes 1.3 quarts. With the car level, I stopped pumping the rear diff as soon as it overflowed, and put the rest of that quart plus another quart into the front diff. The front diff came exactly to the F (full) mark. So 2 quarts fill both differentials if the car is level. If the car is ramped, oil flows to the front of the long rear housing, which will be overfilled when the car is level, and also require buying a 3rd quart for the front differential, of which only a little bit will be used.