('09-'13) Changing differential oil??? - Subaru Forester Owners Forum
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post #1 of 31 (permalink) Old 04-23-2012, 05:46 PM Thread Starter
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Changing differential oil???

Is there any reason to change MT differential oil (front or rear)? The manual says only to inspect yet some posters here change the oils on a regular basis. Opinions?

Thanks in advance.
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post #2 of 31 (permalink) Old 04-23-2012, 06:35 PM
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The rear Diff only holds less than a qt. and comes out fairly dirty looking after 10-15k miles. Changing the trans is an effort to get it to shift smoother.

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post #3 of 31 (permalink) Old 04-23-2012, 06:40 PM
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If you provided info regarding your Forester we could help with more detailed answers.
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post #4 of 31 (permalink) Old 04-24-2012, 02:47 AM
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Originally Posted by SubieOutlaw View Post
If you provided info regarding your Forester we could help with more detailed answers.
+1

Rear differential should be changed at 10K miles and every 20-25K miles thereafter IMHO

Be careful what you wish for.
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post #5 of 31 (permalink) Old 04-24-2012, 03:19 AM
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Quote:
Originally Posted by OldGoat38 View Post
Is there any reason to change MT differential oil (front or rear)? The manual says only to inspect yet some posters here change the oils on a regular basis. Opinions?

Thanks in advance.
Yes. The Subaru Australia service schedule says to change the diff oil every 50,000km (31,000miles) when the gearbox oil is changed. It takes 0.8L.

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post #6 of 31 (permalink) Old 04-24-2012, 04:03 AM
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Quote:
Originally Posted by OldGoat38 View Post
Is there any reason to change MT differential oil (front or rear)? The manual says only to inspect yet some posters here change the oils on a regular basis. Opinions?
The maintenance schedule also says to replace the MT and diff gear oils every 15K miles under "severe driving conditions", such as towing a trailer.

I don't use my Forester for towing, but I'll probably change the gear oils at 30K mile intervals on the odometer, plus an initial change at 7.5K miles. The gears do wear, and I'd just as soon not have that stuff needlessly swirling around inside the MT or diffs.

Note that the MT and the front diff share the same gear oil reservoir; don't use limited slip gear oil for this application. I've tried Subaru Extra-S and Mobil Delvac gear oils; I'm partial to the latter.

HTH,
Jim / crewzer

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09 Forester 2.5X EJ25 5MT Premium AWP PZEV (sold 7/2011)
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post #7 of 31 (permalink) Old 04-24-2012, 04:28 AM
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Here's why I change mine well before 15k, this was done at 11k. The rear diff plug, in profile with the slurry attached to the magnet, and then the slurry transferred to the paper towel. The oil was black as sin as well.

Not the best pictures as they were from my cell phone. But enough to get the idea across. The front diff was about 50% as bad.
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post #8 of 31 (permalink) Old 04-24-2012, 05:33 AM
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Most of your wear particals are generated in the first couple thousand miles of service as things get worn in...that's the main reason to change early.

I changed our 09 FXT at 30k with synthetic, probably won't touch it again (unless we keep it longer than I plan). The OE fluid did drain ugly, but that was expected...I've never seen an OE fill on any vehicle that didn't drain ugly.
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post #9 of 31 (permalink) Old 04-24-2012, 05:53 AM
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True, all of our Subaru's have been consistent.

Since they're so easy I do them every 15k after the 1st one.

At this point, with 70k on it, my wife's 08 OBW diff fluids come out pretty clear with essentialy nothing on the plugs. Probably could stop doing them now but they're so easy I'll keep doing it on the 15's.

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post #10 of 31 (permalink) Old 04-24-2012, 12:04 PM
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Hi, this is my first post here.
I have a 2011 Forester with auto trans. I plan to change all the fluids. The transfer case has a Torx or star type drain plug. Do you guys know what socket I need for this, and where to get one?
Also, What type of oil do I use for the diffs, and transfer case, and trans? Do I need to use synthetic?
Thanks, Mike
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post #11 of 31 (permalink) Old 04-24-2012, 12:09 PM
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It is a T70 bit. Be sure you can remove the fill plug before attempting the drain plug. Often owners have drained the diff fluid only to find out they can't remove the fill plug. Now they are left with a dry diff and no way to fill it.
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post #12 of 31 (permalink) Old 04-24-2012, 12:22 PM
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Quote:
Originally Posted by SubieOutlaw View Post
It is a T70 bit. Be sure you can remove the fill plug before attempting the drain plug. Often owners have drained the diff fluid only to find out they can't remove the fill plug. Now they are left with a dry diff and no way to fill it.
That's not a concern on the front diff.
75W-90. I like Mobil1

Be careful what you wish for.
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post #13 of 31 (permalink) Old 04-24-2012, 12:47 PM
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Originally Posted by fly2mike View Post
Hi, this is my first post here.
I have a 2011 Forester with auto trans. I plan to change all the fluids. The transfer case has a Torx or star type drain plug. Do you guys know what socket I need for this, and where to get one?
Also, What type of oil do I use for the diffs, and transfer case, and trans? Do I need to use synthetic?
Thanks, Mike
If you get an aluminum washer for the front plug, the torque is in the low 30 ft-lbs, and if its the copper washer its around 51 ft-lbs or so. You can find the exact numbers in another thread. The AT plug is around 18 ft-lbs, also searchable in another thread.

Look around for the rear diff plugs and you'll see there are many torques recommended as well, and some people like to use sealant, some don't. I believe ADC recently said he uses 22 ft-lbs. If it works for him, its good enough for anyone.

The AT uses Subaru type HP.

The thing about doing a drain and fill on the AT, and this was very kindly pointed out to me by another member is that there appears to be a special computer controlled purge cycle required after the fluid is replaced.

He referenced the procedure in the service manual, and I found it in my own manual as well. What I'm not clear on is if it pertains to a drain and fill or is only applicable for a full fluid exchange.

Anyone know? I may start a separate thread as more 09 and later owners may want to start doing a drain and fill on theri AT.

Larry D
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post #14 of 31 (permalink) Old 04-25-2012, 06:43 AM
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Quote:
Originally Posted by lfdal View Post
If you get an aluminum washer for the front plug, the torque is in the low 30 ft-lbs, and if its the copper washer its around 51 ft-lbs or so. You can find the exact numbers in another thread. The AT plug is around 18 ft-lbs, also searchable in another thread.

Look around for the rear diff plugs and you'll see there are many torques recommended as well, and some people like to use sealant, some don't.


Make sure you don't over torque the front diff drain plug, they seem very ease to strip the threads in the housing.

I use a coating of never-seize on the fill/drain plugs on the differentials...a steel plug in an aluminum housing is a galling issue waiting to happen, I don't care if they are plated plugs.
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post #15 of 31 (permalink) Old 04-25-2012, 06:46 AM
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Originally Posted by lfdal View Post
The thing about doing a drain and fill on the AT, and this was very kindly pointed out to me by another member is that there appears to be a special computer controlled purge cycle required after the fluid is replaced.

I did a drain and fill on my 09, made no difference. I used HP, and I actually overfilled a tad and needed to siphon some out. That was nearly 10k miles ago...

I will be curious if its needed for a simple pan drain.
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