Yuck! Original gear oil.

[Hollow]

Just changed out the front and rear diff on my Outback with Valvoline Durablend 80w90. From the look of the oil that drained out, and the amount of sludge on the drain plugs, that may have been the factory fluid I drained out at 106,000.

Maintenance interval is inspect every 30,000 miles and replace at that time under "severe" service(defined as: repeated short trips, stop-and-go, extensive idling, rough, muddy, dusty, wet, cold salty conditions, frequent towing).

I meet many of those conditions and so did the previous owner, so I wasn't thrilled that the oil I was expecting to be 40k old seems to be factory.

Should I do a shorter run on this oil to try and clean/flush out the differentials or run it to 30,000 change it? Vehicle drives as good as ever.

 

[mount]

Run it out to 30,000 at least!

Your differentials are still going to outlast the rest of the car, especially with the proactive maintenance you're doing.

The only thing which warrants early changes is a good amount of heavy towing as it heats up the lube.

Make sure to keep an eye on your seals. New fluid often cleans things out so good it starts to seep.

 

[Hollow]

Silly me thinking that the 60k service done by the previous owner included gear oil.

However, all in all, minus the rust seized bolts (stupid salt belt!) this is one of the easiest vehicles to work on I've ever encountered.

 

[Hokiefyd]

With my OCD self, I'd run the Durablend for two OCIs and then change again. Or, if you plan to change every 30k, 120k would be the next "even" interval, so just run it until then when you get on an even 30k interval.

I'm a big believer in sticking with these types of "even" intervals. Engine oil every 5k miles on even 5k mile increments (25k, 30k, etc), ATF every 15k miles or every 30k miles, on those increments, coolant every 50k miles, etc. It keeps maintenance easy to remember; you never forget when you did it last.

 

[Hollow]

I probably will end up changing it out at 130k miles. Easy to remember.

I do about the same thing for servicing, it makes my life easier.
Conventional oil at 5k, synthetic at 7.5k to 10k depending on time and type of service. Plugs checked at 50k, replaced as needed. ATF at 30k. Gear oil at 30k. Air filter at 20k to 25k. Coolant every 30k to 50k.

 

[oggb]

Folks have done used oil analysis on WRXs with the original gear oil at 100,000+ in the manual transmission and it came back fine. I doubt those diffs even noticed.

I changed my WRX's rear diff at 15,000 or so with Mobil 1 75w-140. I'll never drain it again, but I might check it sometime soon. Might.

 

[Jarlaxle]

Just did the rear axle in my Cherokee...replaced the factory fill (whatever that was...probably 75W-90) with Super Tech 75W-140. I cheated...rather than fight very-stuck bolts, I drained & refilled it with a siphon.

Gotta say: That siphon might be the best ten bucks I ever spent!

 

[cchase]

I did not do the first change on my truck until 350,000 miles. Siphoning the stuff out was the biggest pain I've ever dealt with a car.

 

[Hollow]

Subaru are nice. Front has a dipstick and a drain plug. Rear has a drain plug and a fill plug.

Only problem was the rear drain plug was REALLY rusted seized. PB Blaster, hit with a hammer, nothing. Actually got a breaker bar, and put the jack under the bar and started jacking it up. Lifted the rear tires an inch off the ground by the breaker bar with the jack before the bolt broke loose.

This is why I hate the rust belt.

 

[ron917]

Subaru rear diff plugs have a RTV sealer on them from the factory. That makes them very difficult to break loose. The FSM says to use a sealer when re-installing - Permatex Ultra Grey is the commonly available equivalent. I don't see any need for a RTV sealer on those plugs. I use a non-hardening pipe thread sealer that is spec'd for oil (most of them are, along with water, air, etc).