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Old 01-19-2013, 06:24 PM   #1
SubieWolfSti
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Subaru Stars Differential and Trans Fluid Lesson For STI Owners

Hello Everyone,

The purpose of this, is to inform owners of their vehicle's fluid requirements. I will only talk about the Trans and Diff. Fluid based on my experience in the hopes that this does not happen to others.

I am the 3rd owner of a Subaru WRX STI, a few days ago a came across a clunking noise coming from my car, after further inspection and diagnosing, i pinpointed the noise was coming from the Diff. The Previous Owner decided to change the gear oil with fresh fluid, thankfully he recorded this to which he used Valvoline 75w-90. This was the cause of the problem, as i will soon explain.

According to the OEM Service Manual for a 2006 MY (Section 6 Chassis-- 04.Differentials- DI-19 (page 19))
The Regular Impreza, and WRX take,
GL-5 75w-90 or Equivalent
The Subaru STI takes,
GL-5 SAE 90 or Equivalent (Straight 90 Gear Oil)

Some will argue that it doesnt make a difference, but consider this, if the it didn't matter, why would the manufacturer explicitly state to use SAE 90?
Because, thats what that system was designed for. (in addition to the car being the Sport Edition of the Impreza that many will drive either aggressively or track it or both.)

Another possible argument is that its hard to find, currently Redline and Torco do not carry SAE 90 Gear Oil. However, Royal Purple apparently has SAE 90 but their online distributers do not. Im currently in the process of getting it and will report on my findings. However, If it's not possible to find a high quality SAE 90 oil, then just go to the dealer and buy it or order it.
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Last edited by SubieWolfSti; 01-19-2013 at 09:06 PM.
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Old 01-20-2013, 12:45 AM   #2
Unabomber
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You are overthinking after the previous owner underthought. Buy whatever oil is available as blingy 90 weight is NOT needed. There are some on here that will face palm your Royal Purple choice specifically.
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Old 01-20-2013, 08:10 AM   #3
Aaron'z 2.5RS
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Subaru Extra-S


There, your life just became "easier" ... boom
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Old 01-20-2013, 09:07 AM   #4
HeroCrank
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Quote:
Originally Posted by Aaron'z 2.5RS View Post
Subaru Extra-S


There, your life just became "easier" ... boom
Thumbs up. I endorse and support this suggestion.

Last edited by HeroCrank; 01-20-2013 at 10:22 AM.
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Old 01-20-2013, 09:14 AM   #5
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Extra-S is so sexy. I bought the whole 5 gallon thing of it and changed the fluid on both my Subarus. My 14 year old Impreza's original tranny with 264k on it is as smooth as butter!
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Old 01-20-2013, 10:53 AM   #6
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According to this: http://forums.nasioc.com/forums/show....php?t=1631770 the 06 requires LSD oil and some posts suggest it will clunk without something that has the friction modifier. I don't have an STi, so I have no idea!
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Old 01-20-2013, 04:28 PM   #7
SubieWolfSti
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I agree with the fact that i may be overthinking it, and i agree that RP is a tad too excessive, but my view of it is, if the car wants straight 90w then that's whats it should get right?

As for fluids i will go for the Extra-S, thank you for the info regarding it. I preffer OEM to much else out their, and it makes my life easier.

Thank you ladies and gentlemen.
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Old 01-21-2013, 02:13 PM   #8
SubieWolfSti
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-Update-

Well the rear Diff is getting the OEM LSD Fluid so that was settled.
However, after talking with subarugenuinparts.com apperently they do not make
Extra-S in straight 90 oil for my trans.
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Old 01-21-2013, 05:20 PM   #9
2dino
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Ask you supplier for Subaru rear LSD oil, not gearbox oil.
I believe it is Gear oil LSD Part No. K0305Y0900
It is in 1 litre metal can.
It is nothing to do with Extra S at all.
That was specified for the rear differential when I had my 04 Sti.


Extra S comes in 75-90 and there was also a 75-80(?) version.
75-90 is what we want for gearbox.

cheers
2dino
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Old 01-21-2013, 07:03 PM   #10
SubieWolfSti
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The part number matches the oil i ordered from the dealer so the rear diff. is taken care of.

However, from what i understood from the manual, Subaru wants straight 90w for the trans aswell. (Section 05. Transmission - 05. General Description 6MT-2 (page 2)).

The bummer is that they dont sell it, they buy in Bulk (Huge Oil tank Truck) which i have a suspicion that they use 75w-90 to saves costs instead on storing 90w exclusively for the STI cars. (Food for Thought)
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Old 01-22-2013, 12:37 PM   #11
2dino
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Don't have 06 shop manual but I am only aware of Subaru listing GL-5 gearbox oil.

Extra S 75W-90 is the OE oil and is used from 04 till now.
If dealer put Extra S 75W-90 you have the correct oil & good to go!

Not aware of Subaru using straight wt. gear oil for gear box.
Can you post scan of the manual?
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Old 01-22-2013, 03:36 PM   #12
SubieWolfSti
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(I Dont Own This, For informational Purposes Only)

Here it is,

If you notice the (5) next to the 90w gear oil and on the bottom pretty much saying the STI model only.
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Old 01-22-2013, 05:20 PM   #13
2dino
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Interesting.
So it is from 06 factory manual?
Thanks for sharing this another Subaru mystery


Still I would worry less about it.

I actually would worry about straight 90 gearbox oil for year round drivability in winter.


So glad when my shops started stocking Extra S.
I was not happy with Motul in my 04 Sti.


Cheers
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Old 01-22-2013, 09:59 PM   #14
SubieWolfSti
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Just got a call from the dealer, apparently they do not make the LSD oil for the STI in 1 liter cans anymore. It is as of a month or two ago ordered in bulk form.

Luckily, they are some online, and i got the extra-s for the trans. so now to play the waiting game.

Hope this helped somebody.
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Old 01-11-2014, 08:25 PM   #15
STIinthefe
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My 04 sti started to have a slight synchro grind up shifting to 5th and down shifting to 4th. after a couple weeks of research I changed the tranny fluid to Motul 300. I must say that the shifting is much smoother overall BUT I still have my up 5th and down 4th grinds. I may try a cocktail next time, i heard of so many having luck with this fluid or cocktails but when i read the service manual it says do not mix different manufactures of fluid and it scared me off.
PS i know there is a ton of info about this, but I just wanted to add my experience.
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Old 01-12-2014, 01:30 PM   #16
SubieWolfSti
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Default The extra bits of info that count,

Hey STIinthefe,

No worries, I also wanted to add my expirience. As for a cocktail, i wouldn't recommend that because each bottle has their own additive which when mixed together with other brands can cause issues. I installed Extra-S on my STI and i love it, and feel confident when driving. Furthermore if this helps, i seriously track my car and am proud to say i have not had any differential issues or transmission issues.

Cheers
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Old 01-13-2014, 07:10 PM   #17
STIinthefe
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^ thanks. gonna let the motul ride till the next change but i will use that fluid next time and in the rear diff when i change it in a week or so.
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Old 03-21-2021, 05:09 PM   #18
willowlee
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Bringing back this thread cuz i don't want to clutter the site with a new one. It's time for me to change my fluids. They are the front and rear differentials, and also the transmission gear oil. I have a 2013 subaru sti. From what i have been reading online, all three front, rear, and transmission gear uses the same subaru extra s 75w90 oil? Or is there different oils from subaru for each? I just plan to keep it oem, nothing fancy here. Thanks.
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Old 05-14-2021, 09:50 AM   #19
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I've been running the Scottys cocktail in my 04 STi trans. 11k miles no grinds or issues, 3qts of motul gear 300 75w90 and the rest (1.8ish qts) redline lightweight shockproof. Then again I didn't have any grinds or issues to begin with. No complaints though it shift smooth as ever
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