[Subaru3025]

2014 Forester, 9 1/2 years old, approx. 75,000 miles, no severe driving

Front and read differential oil question:
Forester maintenance manual indicates the 2 differentials should be periodically inspected and oil replaced only if the car has experienced severe driving. This car has not.

My Subaru dealer told me that the oil must be replaced every 50K to 75K regardless of how it is driven.

Sooo - should I follow the dealer & replace the oil in both (or maybe just rear) differentials?
Or follow the maintenance manual & just inspect?

Thank you.

 

[TAMUGRAD2013]

You will probably get a lot of different answers to this, but to me changing fluids is cheap insurance, changing the whole differentials down the road is expensive. In my previous Outback I would change front and rear about every 36,000 miles on my own at my friends home shop. Yes it took about and hour to do, but it was not hard and it was good insurance knowing the fluid was fresh. The front fluid never seemed to dirty, but the rear fluid always seemed pretty brown and and discolored, but never burnt. On my Forester I will do the same which will probably happen for the first time in May.

 

[bman400]

You'll get responses from changing religiously every 30,000 miles to 100,000 miles. Balls in your court and do what you feel comfortable. Both are DiY tasks if you want to save $

 

[Black21Limited]

If you decide to do it yourself always break loose the fill plugs where applicable before attempting the drain plug. They can be very tight in some cases.

 

[donkpow]

I'd change the oil if it hasn't been done to date.

 

[adc]

Change them. Especially the rear

 

[Canuk]

There is no such thing as a lifetime fluid. Anywhere. Period. Change the diff oil, and do the tranny while you’re at it.

 

[whobodym]

Two further observations - 1) some dealer service departments definitely exaggerate the necessity of some service procedures for profit 2) have we seen any stories here on the forum directly saying "I drove my car always gently for x0,000 miles and I did have differential failure because of never changing fluid"? I myself had it done - but only because I did 10,000 miles of towing (all on one trip, taking my car from 37,000 to 47,000 miles) and I'm now at 92,000 miles with no sign of driveline problems.

 

[Theseus161]

I would definitely change diff oil every 30k to 40k miles. It starts to look really bad if not replaced. All automotive lubricants will break down in time. It’s easy to replace and not expensive. I’d stick with Subaru oem.

 

[Rand]

Change it in both esp. the first time there is alot of extra break in wear in there.
Its easy to do with a few simple tools.
I recommend Valvoline in the squeeze bags.

I plan on first change around 20k miles.. then every 30-50k miles. Its very reasonable $$ if you are just paying for oil.

 

[Phil From Texas]

I suggest changing the fluid in both the front and rear. Don't forget the cvt fluid. That should be changed every 60k miles. I had a complimentary oil change with a recall. I was given a list of all of the fluids that were checked. I found out that meant a visual check was done (or was it?) to see if there were any external leaks. What a joke.

 

[Natedog]

After owning a 2015 with the CVT, a 2010 and now 2012 (both non CVT), and many other cars over the years, I'd do both front and rear diff fluid changes every 30k miles maximum. Mine were both dirty everytime at around 30k miles (front was worse on mine), the CVT every 30k maximum...it was nasty dirty everytime I had it changed which ranged from 30-40k miles in between the three changes.

Diffs are easy DIY if you're mechanically inclined, CVT is not too difficult either but you must be detail oriented and have some wrenching experience...otherwise leave it to the pros. Pay em now...or pay em a lot more later on!

 

[MarkL]

You could either have the fluid analyzed before you do the change, or send some after the change to see what the condition of the fluid was. I use Blackstone labs. Or you could do the simple test and extract a little out the filler hole- if it's black you know for sure it's past time to change it. Moisture can get into your diff fluid just from condensation inside the case. Once you get much moisture in the fluid it can accelerate the fluid breaking down.

 

[Black21Limited]

The rear doesn't hold much. It's not worth sending to the lab just to see if it needs changed. You would be down by a bit to fill the bottle, without replacing what you drained. It would be worth it to check for wear though. But I would only send it after I went ahead and changed the .8 quart. At least you'll be driving around with fresh oil waiting for the results.

It's not like there is a drastically expensive amount of gear oil involved with both front and rear combined. Under 4 quarts in most cases. (2.2 quarts for the 2021) If they held something like 4 quarts each, going a longer distance would be much more forgiving. But since there is such a small amount, there isn't much "reserve" if something is going south.

 

[PMRsForester]

@Subaru3025,
Change the differential oil. It’s done its job. Unless you want to have an oil study on it, but why…. Just do what is in your manual. Myself, I change the oil every 30k as I live in snow country.

 

[Vishnu]

Do what Subaru recommends. Just check the levels occasionally. The oil is good forever unless contaminated. If you find leaks that means dirt has an entrance point and the leak needs to be fixed and a new fluid fill. Dealers enjoy your money and probably could care less if it's a waste of money or not no matter how sweet they are to you.

 

[Wangle]

You could either have the fluid analyzed before you do the change, or send some after the change to see what the condition of the fluid was. I use Blackstone labs. Or you could do the simple test and extract a little out the filler hole- if it's black you know for sure it's past time to change it. Moisture can get into your diff fluid just from condensation inside the case. Once you get much moisture in the fluid it can accelerate the fluid breaking down.

I am sorry, and I do appreciate your perspective, but it seems silly to me to test what amounts to be a total of 2.2 to 2.3 quarts of oil that gets changed so seldom. On Subarus that tow I change front and rear fluid at 25 to 30K. Otherwise 50,000 miles. This is one of the most neglected things. Next week I’m going to help my nephew who lives out of state change differential fluid at over 190,000 miles. I hope it actually drains out LOL.
CHANGE IT!!!

 

[Vishnu]

I apologize, but my owner's manual is not in a convenient location, but I think Subaru does allow that towing counts as severe duty, but I don't know if that means the differential fluid change is specified or not. My basis for not recommending non-specified changes is two fold: 1. Subaru doesn't think it's necessary and their engineers signed off on the maintenance requirements, and 2, Your two or three quarts of oil represent a lot of natural gas to produce that synthetic oil and multiplying your quarts possibly being wasted by the millions of vehicles out there results in an astronomically big waste of resources. Recycling even consumes energy. I will admit that I have been known to swap out differential oil, but usually around the two hundred thousand mile mark. I buy new cars for the warranty and then drive them to death. Many had been driven over four hundred thousand miles before selling them and not one of the dozen or so vehicles have ever had differential problems. I never changed the CVT fluid in my '14 Forester and it is still going for my daughter with over 300,000 miles. But I did change the differential oil at the above mileage. Engine oil would last forever too if it weren't for the blow-by combustion contamination that results in the oil becoming acidic and other nasties that eat bearing inserts.. There is no such contamination in differentials or CVTs. Regular automatic transmissions and limited slip differentials have friction material contamination that necessitates a periodic change out, but there are no such contaminates in non-limited slip (Subaru) differentials.

I just replaced a transmission on a GM half ton truck with 350,000 miles on the odometer and always followed the schedule on the filter and fluid, but it gave out. Point being that maintenance, or over maintenance, doesn't guarantee longevity

 

[Black21Limited]

70 plus years of not changing the diff oil in our M37 wiped out the rear differential at 17,000 miles.

Just because there are better lubricants now, there is no study on them for that time frame.

The fact is as long as the differentials/transmissions
are vented to the atmosphere, there is going to be moisture and oxidation. Nothing lasts forever, as the PO's of our M37 assumed.

Which includes the military, the city of Parma and a private individual. All who failed to do a simple drain and fill.

 

[Vishnu]

70 plus years of not changing the diff oil in our M37 wiped out the rear differential at 17,000 miles.

Just because there are better lubricants now, there is no study on them for that time frame.

The fact is as long as the differentials/transmissions
are vented to the atmosphere, there is going to be moisture and oxidation. Nothing lasts forever, as the PO's of our M37 assumed.

Which includes the military, the city of Parma and a private individual. All who failed to do a simple drain and fill.

Was the BMW differential a limited slip? Probably yes if it's a BMW. LS's have friction material which contaminates the oil eventually and definitely do, as mentioned in my post, require change-outs periodically. The maintenance schedule also probably had a differential oil service line to address the issue the PO ignored.
That was a costly error passed on to you by the PO. In most likelihood the PO didn't trust the BMW engineers and thought themselves the wiser ones, or else they didn't care.