I recently passed 30K miles on 2016 2.5i Premium. So I drained and refilled the Front and Rear Differential fluid today, and thought I would document my journey and add some observations that might be helpful to other noobs like me!
First, I have the FSM for my car, so I carefully studied the manual and read up on the wonderful how-to threads in this forum. Thank you to everyone that posted, it was very helpful!
Here is the gear oil I used from wally-world. It is GL5 and meets the specs in the manual:
I lifted up the car and placed it on four jack stands. This gave me enough room to to get my breaker bar on the plugs. Without the car being lifted on jack stands, I didn't have enough room to turn the breaker bar. The fill and drain plugs are clearly marked with a yellow dot. The top plug is the fill and the bottom is the drain.
Both plugs are a 10mm hex socket and I had to use a 3/8 inch breaker bar to break them free.
The oil that drained out of the rear differential was a disgusting looking grey fluid. It looked very dirty. The drain plug has a magnet to catch the metal sludge. Here are the plugs before cleaning them:
I cleaned up the plugs and replaced both gaskets per the FSM recommendation.
I replaced the drain plug and tightened to spec - 36.9 ft lbs.
To refill with new gear oil, I rigged up some tubing to the spout of the bottle. The tubing had a tendency to come off the spout, so I had to add a zip tie to hold it on tighter. Luckily, there is a small ridge that goes around the spout of the bottle that I could use to hold the zip tie.
I fed the end of the tube into the filler hole and squeezed the bottle to feed the oil into the differential. It worked quite well, with minimal spilling. It took nearly the entire quart bottle, although the specs call for 0.8 quarts. I did lose a little from the hose, so I think this is why I used nearly the entire bottle. Once I started getting a small stream from the fill hole, I closed up the filler plug, tightened it to spec and moved on to front differential.
The front differential is little more challenging to get to. First, I pulled off the front passenger side tire so I could get to the fill plug.
I read and took the advice of those before me to check and make sure that you can break the fill plug free before draining the old oil out! This would have been much easier if I had an extension set for my breaker bar. You need a good set of extensions because there isn't much room to play around in there. Luckily for me, I was able to get my breaker bar in behind the exhaust and break the fill plug free. This was an 8mm hex socket.
Next, you have to remove the front under cover - transmission in order to gain access to the overflow plug and the drain plug. There are 5 screws and 2 clips to take out. I had to print the page from the FSM and bring it with me to figure it out since it was my first time. Here is pick of the under cover directly below where it sits on the car. This is a view from the front drivers side.
With the front under cover - transmission removed, you have easy access to the overflow and drain plug. The overflow plug was an 8mm hex and the drain plug is a 70 Torx. The Torx Drain Plug is clearly marked as Diff Oil.
When the oil drained out, it didn't look bad at all. It had a nice golden color to it still. This was much different than the oil that drained from the rear. The front drain plug also has a magnet to catch the metal sludge.
I cleaned it out and replaced the gasket. This gasket is a different part number than all the others.
After draining the oil and cleaning the plug, I replaced the drain plug and tightened it to spec - 51.6 ft lbs. I left the overflow unplugged because you need to fill the differential until there is a small stream from the overflow plug. This part was pretty straight forward. I filled the front differential using the same vinyl hose setup as the rear differential. It took between 1.4 and 1.5 quarts, exactly according to the specs. It was much easier to fill the front as my hose was long enough to reach into the fill hole and still allow me to hold the bottle up and squeeze the oil out.
Finally, I closed up the overflow plug and the fill plug. I couldn't get my torque wrench onto the fill plug because there wasn't enough room, so I tightened it as much as I could with my ratchet.
First, it was very easy once you have it figured out. The hardest part is getting started! I would recommend having a good set of hex sockets (10mm and 8mm) and a T70 Torx bit.
Very helpful would be an extension set that fits your hex socket set. This would be especially helpful with the front differential fill plug. You need about 20 or 24 inches of extensions to reach that plug. Torque wrench is a must!
The rear diff oil was disgusting and I should have changed it much earlier. So if your wondering if you should change it early, I say go for it. The rear is very easy to do. The front diff oil still looked good and I'm glad I changed it out before it got too bad. I will probably drain and replace the diff oil every year as a routine maintenance item.
Finally, the FSM is extremely easy to download from the Subaru Technical Information site. A three day subscription only costs $35 and you can download the entire manual plus additional training documents. I would highly recommend it.
Hope this helps someone!