kinda forgot to change differential fluid...

[2016subbforest]

thanks in advance for reading.

2016 subaru forester 2.5L base model...

i have 45000 on it right now. the maintenance manual says i should be "inspecting" or changing (i guess) every 30,000. BOTH the FRONT and REAR differentials. i'm a little late. i drive in "NORMAL" conditions... don't toe anything, etc...

will an oil analysis tell me anything about damage done? i plan to do a blackstone labs analysis, but i'm reading i should probably go with dyson? anyway... everything works fine. just forgot. i purchased the thing brand new, so this will be the first gear oil change.

 

[JHZR2]

Most folks never change differential, brake, or power steering fluids....

What major wear chunks that were created, were created by 1500 miles (BMW used to recommend a 1200mi change, IIRC). What breakin was done by 7500 miles (my Chevy truck recommended that for the first change). Anything past that just is what it is. It’s not going to get progressively worse because you changed at 30 vs. 45k. And it’s not an old vehicle, so it’s not a major concern from ambient oxidation or breakdown.

I woudon’t do a UOA. Inspect might mean just check the level, but if you change it when you have a chance, you’ll be ahead of the game.

No damage done and only benefit from here, IMO.

 

[JimPghPA]

Maybe some one with a background in Subaru's can give you more specific info, but if you are not noticing any kind of problem such as back tires chirping because clutch in rear end not slipping properly while the vehicle is going around turns, then you probably have not caused any harm. If it does do that the fix is to change the fluid, and then drive backwards in both left and right circles until the tires stop chirping.

 

[Capt]

It’s Fine, Im sure some people never change it! Lol. I just changed diff fluid in a Ram 3500 that tows 12k lbs frequently, 135,000 miles never changed... it looked like new fluid and very little ”metallic dust” on the pan. Owners manual says change Every 15,000 miles “severe service“ -towing, heavy etc. 75w-90

 

[Oro_O]

I have had several different kinds of awd cars and a 4wd truck for 25 years. As a general rule, I have changed the diff fluids at ~40k on each. I do this as I have no ownership "horizon" and may keep them quite a long time and thus do maintenance in that mindset.

If it were mine and I wanted optimal care, I'd change the fluid now and then base my next change interval on how it appeared. Unless you are in a very cold climate, an 80w-90 may be more suitable than the recommended "one-size fits all" 75w-90. If you have a clutch-type lsd differential, I would ask other owners what/how much LSD additive it tends to require.

Gear oil in a differential does not undergo contamination like engine oil does - it appearing "clean" is no guarantee it's still protecting. It is subjected to extreme shear forces on gear teeth at all times and you can't take an "it looks fine" approach to it.

 

[slacktide_bitog]

Welcome to BITOG

As others have said, most people never change the differential fluid, and they arrive at the junkyard on their factory fill.

Changing it at 45k is fine, no problem at all, and still way more often than most people change it anyway.

 

[kschachn]

thanks in advance for reading.

2016 subaru forester 2.5L base model...

i have 45000 on it right now. the maintenance manual says i should be "inspecting" or changing (i guess) every 30,000. BOTH the FRONT and REAR differentials. i'm a little late. i drive in "NORMAL" conditions... don't toe anything, etc...

will an oil analysis tell me anything about damage done? i plan to do a blackstone labs analysis, but i'm reading i should probably go with dyson? anyway... everything works fine. just forgot. i purchased the thing brand new, so this will be the first gear oil change.

Since you have nothing to compare against, a UOA would be relatively new useless at this point. Even if you are somehow able to determine that damage occurred, what would you do about it except to change the fluid? Change out the fluid now if you wish and move on.

 

[barkingspider]

Just change the fluid when you have a chance and you should be fine.

 

[Skeet6]

Just change the fluid when you have a chance and you should be fine.

^^ this. It's easy, dump and fill them.
Mike B

 

[doublebase]

I wouldn’t waste my money on an analysis, you went 15,000 miles over the “inspect or replace” fluid recommendation. Keep in mind that most people are just going to inspect (check the level) and not replace. So in all honesty, changing it at 45,000 miles is most likely more than ok. And what is that analysis going to tell you anyway? Worst case scenario (and this isn’t going to be the case anyway, trust me), they tell you you’ve damaged your differentials. What are you going to do about that? Replace them? They won’t be under warranty because you missed the recommended change/inspect interval.

You’re car is probably running and driving mint...and that’s because it is. Don’t worry about it.

 

[SubieRubyRoo]

Gear oil doesn't have to deal with the same level of acids like engine oil does, so "in general" gear oil will stay viable much longer. Subaru differentials aren't known to be very hard on fluids, especially the NA models. The gear oil will stink, and will likely be as dark as the look your wife gives when you roll in at 2am after not answering your phone all night, but other than that nothing will be harmed.

Because the stress level on the gear oil is not that high, you can pretty much use any one you want, but I'd stick to synthetic at a minimum. Motul Gear 300 is my personal favorite, but it's spendy. Amsoil Severe Gear will likely last the lifetime of the vehicle for an average person, and of course you've got the big-box choices (Mobil, Valvoline, Castrol, etc etc) and they are all fine too if you're buying based on cost.

No need at all for a UOA, since it doesn't really matter anyways. What's done is done, and in reality a UOA on this app would likely just make you worry about a nothingburger. For the $38 at Blackstone you can change the gear oil twice, and for Dyson's cost you can likely do oil changes for an entire year or longer.

Just change the gear oil, your Forester's diffs will easily go another 300k miles in highway service without a peep of trouble!

 

[Hall]

the maintenance manual says i should be "inspecting" or changing (i guess) every 30,000.

I don't know what your manual says but you quoted "inspecting" the differential fluid. I'm sure that for most manufacturers, that means "check the level". Otherwise, how do you inspect this fluid ? Suck some out and visually look at it ? Confirm what the manual says or if it makes you feel better, just change it.

 

[badtlc]

change it and dont worry. The rear diff isn't hard on fluid. After two changes you probably never need to change it again.

 

[The Critic]

Just service it.....differential fluid in light duty vehicles such as these are rarely an issue. You will need a full torx set to tackle this job though. IIRC the front differential is a bit of a pain to fill.

 

[DougR]

Just change it. You must open the fill plug first. If you drain the fluid and then you are unable to open the fill plug, you'll have to tow the vehicle to a shop. I changed my diff fluid at 90K when 60K was recommended. The drain magnet had very little metal on it and the old fluid was almost as clear as the new fluid.

 

[Kira]

JimPghPA said above: " If it does {chirp} the fix is to change the fluid, and then drive backwards in both left and right circles until the tires stop chirping."

Is this to work any debris free?

 

[ctechbob]

JimPghPA said above: " If it does {chirp} the fix is to change the fluid, and then drive backwards in both left and right circles until the tires stop chirping."

Is this to work any debris free?

Most likely to work the new fluid (Which will have new FM in it) into the clutches to restore normal operation.

 

[nobb]

Out of all the fluids in a vehicle, gear oil is probably the one that you can delay/forget to change well beyond the recommended intervals with little to no harm.

 

[Chris142]

In late 1968 mu dad bought a brand new 1968 Plymouth Valiant. He drove it fron then untill the late 90's.

About 30 years and 150k. He parked the car when it began oil fouling spark plugs.

He never touched the diff oil.

 

[AutoMechanic]

Never changed differential fluid in anything I own. Haven’t had any problems with anything. I would do it it’s just it sucks when you have to do everything on ramps or Jack stands since I don’t have a home garage. And it sucks if you can’t find a gasket and have to use RTV.