[07STILimited]

Soon it will be time for me to change my transmission and differential fluids. I have read a lot of different threads about it and I am a little confused about what to buy. For the rear diff many people have said that you need to use Subaru Limited Slip Differential Oil (Part# KO305Y0900) because normal gear oil does not contain friction modifiers. Since my car is an 07 and uses a torsen rear diff instead of the older clutch version do I still need to use a limited slip diff specific oil? I'm thinking that since the front differential isn't a clutch type and it shares its oil with the transmission I probably can just use normal gear oil in the rear diff. Are there any advantages/disadvantages to using an oil with friction modifiers for this type of diff?

My second question is about the type of gear oil to use. After reading numerous posts about this I have decided that I want use oil that is as close to the stock oil as possible. Many people claim that Subaru uses congenital Valvoline gear oil. Others say that Subaru does not use Valvoline and Subaru Go Extra S (part# K0322AA093) is much better. I would love to use Go Extra S, but it is only sold in 5 gallon drums. What is my best option if I want to use something similar to stock?

My last question is do I really need to change this oil at 30k? I checked it an it is very clean. It is almost completely clear. Is it still a good idea to change it anyway?

Thanks

[Deuce Cam]

I contacted SOA regarding which transmission oil they use in the the STI and they responded saying they use the GO extra s in all their manual transmission cars from the factory. Unfortunately, as you know it's not practical to buy a five gallon drum of it (unless you rack up 60-90k miles a year). FWIW, this fluid is not a full synthetic, although it may have synthetic additives.

I would stick with the Subaru lsd oil for the rear ssuming Subaru is still using this fluid for the torsen diff. You know it works and it's readily available, why switch?

[07STILimited]

Originally Posted by Deuce Cam

I contacted SOA regarding which transmission oil they use in the the STI and they responded saying they use the GO extra s in all their manual transmission cars from the factory. Unfortunately, as you know it's not practical to buy a five gallon drum of it (unless you rack up 60-90k miles a year). FWIW, this fluid is not a full synthetic, although it may have synthetic additives.

I would stick with the Subaru lsd oil for the rear ssuming Subaru is still using this fluid for the torsen diff. You know it works and it's readily available, why switch?

Thanks for clearing that up. I'm glad I at least know what the factory oil is even though it's difficult to obtain. I read that it is basically a highly refined/processed conventional oil which makes it close to what some companies would call a synthetic (even though it clearly isn't a true full synthetic). This leads me to believe that a normal conventional gear oils (such as Valvaline) may not be very similar to Go Extra S which makes me reluctant to use a different oil. Did you end up choosing a transmission oil yet?

I agree with you about the diff oil. Assuming Subaru uses this oil for the 07 torsen diff I am happy to spend the $20 on it. I'm just not sure that's what Subaru still uses. From what I read friction modifiers are only needed with a clutch type diff. Maybe I will contact SOA about this one. Could you tell me the best way to get a hold of them? Thanks!!

[Deuce Cam]

I'm at 17k and looking to change those fluids, I'm still trying to decide on a transmission fluid to go with. As you know it's not an easy decision. I've been reading on here and nasioc and it seems everyone likes to use something different. One guy says something works, twice as many people respond saying it didn't work for them. The two most popular seem to be the Motul 300 and conventional valvoline; although many people have also noted having bad experiences with these oils in the 6 speed. The only thing that seems proven is the GO extra s; too bad Subaru doesn't really make it accessible to the consumer.

I actually complained to Subaru about this fluid's inaccessability and the lack of knowledge of this fluid from my 4 local dealerships (none of the dealerships knew what the stuff was and couldn't even look it up without a part number).

They responded saying it's not readily available through dealerships because there's no demand. I found this response humorous because Subaru makes their rear lsd oil, coolant and ATF (also probably, brake and ps fluid) readily available in small quantities (i.e. quart/gallon jugs). How can there be a demand for these fluids and not the manual transmission fluid?

end rant.

[07STILimited]

Well apparently you had better luck with SOA than I did. I emailed them a very specific question. I asked what kind of oil my rear differential came filled with from the factory. They told me that they were not in a position to answer this question "by mail, email or phone." they told me to read my manual (which obviously doesn't help since it does not state what is used) or to contact my dealer. My dealer is completely useless though. I needed a crush washer to change my oil and after 20 mins of trying to figure it out they sold me one for an automatic transmission! I wish someone on here could tell me what the torsen diffs were filled with from the factory. Here is my email to SOA followed by their response:

Me:

"I just wanted to find out what type of oil my rear differential is
filled with from the factory. My car is a 2007 STI Limited. It is my
understanding that in 2007 the rear diff was switched from a clutch type
diff to a torsen. I know the older clutch versions were filled with
'Subaru LSD Oil Part# KO305Y0990' because they required friction modifiers
to function correctly. Since the 2007 diff is torsen does it just use
normal gear oil (Go Extra S Part# K0322AA093) like the front
diff/transmission or does it require the Limited Slip Differential oil? Thanks"

Subaru:

"Thank you for your e-mail inquiry regarding technical information on
your Subaru STI Limited. We are not in a position to offer technical
information via phone, mail or e-mail. Please refer to your owners manual
pg11-21 thru 11-23. For additional information please refer to your
Subaru dealer. Your local Subaru dealer would be in the best position to
offer technical information regarding your vehicle, as they can give you
a more precise answer to your question.

We hope that this information is helpful in your search for technical
information for your Subaru. Should you have additional concerns please
call me at 1-800-SUBARU3 (1-800-782-2783).

Best wishes,

Gretchen Atkinson
Subaru of America, Inc.
Customer/Dealer Services Department
--------------------------------------------------------"

[Deuce Cam]

I spoke to SOA recently via email regarding the issue I mentioned, I'll see if the guy I'm dealing with can give me a straight answer to your question. I was suprised at the response I received. Overall, they could do nothing about it, but they at least put the stock GO question to bed.

[07STILimited]

Thnx Deuce! It would be great if he was able to answer that question. I'm surprised that with the amount of people on these forums and the vast amount of technical knowledge no one really seems to know what kind of fluid goes in the diff and trans. I'm glad you were able to clear up the trans oil question. Now if I can just figure out the diff oil I'll be set. I think if my diff ends up taking the Go Extra S I might just buy the big drum. The other thing that surprises me is that there is no demand for the Go Extra S. It seems to be the only stuff that is guaranteed to keep the trans operating correctly. There should be a huge demand for it IMO.

[Deuce Cam]

I was considering getting the drum but I've decided that it's just not practical for me. I plan on doing the change every 15-20K (it took 2 years for me to reach 17.5K). The drum would be good for 3-4 fluid changes. There's no guarantee that transmission fluid will stay good for 2 to 4 years in a resealed container so no go for me.

I'm leaning towards the conventional valvoline 75w-90 gear oil, but I still hesitant to actually do it. If it doesn't work well I may try the motul.

As for the Torsen is it mechanical or helical? I think the 04-06 STIs had mechanical (clutch/type) rear lsd.

[07STILimited]

I didn't think about the fact that the oil may break down over time. I just assumed that since it stays good in the car for quite a while it'd be fine in the drum. It would certainly take me years to use the whole drum though. Anyway, I believe the Torsen diff in the 07 uses crossed axis helical gears and does not contain any clutch. This is where I get confused. I thought that friction modifiers were only for clutch type diffs, but I'm not 100% sure. If I can't get the answer from Subaru my next idea is contacting JTEKT Torsen North America the makers of Torsen diffs. It seems silly that getting an answer from Subaru is so difficult. I'm assuming only they know what it is filled with at the factory.

[Deuce Cam]

Well I finally got a response from SOA for your question. It seems you were on the right track. Subaru uses the GO extra S for the torsen rear diff on the 07's, not the mechanical rear lsd oil used on previous years.

Here's a copy of the email trail:

Hello Richard:

Thank you for your patience. I researched this in our Technical Service Manuals. No, the LSD gear oil used in your 2006 WRX STI is not used in the 2007 WRX STI. In the Technical Service Manual for your 2006 WRX STI Sedan, it states:

Mechanical LSD oil MUST be used for STI model. Recommended oil - Gear oil LSD (Subaru part # K0305Y0900), GL-5 (90) or equivalent.

In the Technical Service Manual for the 2007 WRX STI Sedan, it states:

Recommended gear oil: GL-5 (75W-90) or equivalent.


For the 2007 WRX STI, the Subaru Extra Gear Oil (75W-90) was used at the factory for the rear differential and manual transmission.

I tell you what Richard, I sure do like the 2008 Technical Service Manuals as there are separate ones for the Impreza/WRX and WRX STI. Makes reviewing the information so much easier as it is specific to the unique WRX STI.

Sorry again about the delay. Have a great day!

Sincerely,

John
Subaru of America


From: John
Sent: Tuesday, May 06, 2008 3:48 PM
To: 'Richard'
Subject: RE: 00-General Inquiries (E-mail #)

Hello Richard:

Sorry for the delay. There were some changes here at Subaru of America that happen to have increased my workload about tenfold at least for now. I would be happy to help you and your friend with this. Just give me some time to properly research this. I will be back in touch shortly.

Thanks for your patience and for your kind words about the service I provide.

Sincerely,

John
Subaru of America

From: Richard
Sent: Saturday, May 03, 2008 7:50 PM
To: John
Subject: RE: 00-General Inquiries (E-mail #)

John,

I'm writing in regards to a question my friend has about his 2007 STI. He contacted SOA regarding his question, but his representative did not know the answer. You were a great help in providing specific info on my questions regarding the extra s GO so I thought you could help.

I know Subaru offers and uses their own rear differential lsd oil from the factory on all cars equipped with a limited slip differential through 2006. In 2007 Subaru changed from a standard clutch type rear differential to a Torsen rear differential in the STI model. The difference, I have no idea. My friend wants to know if Subaru is still using their rear lsd oil for the Torsen differential.

My question, what rear differential oil is used in the 2007 STI from the factory?

Thank you,
Richard

Edit: Done to remove personal info.

[07STILimited]

Richard,


Thanks a lot for contacting them on my behalf! I really appreciate it! I was assuming it was the go-extra s, but I wasn't able to verify this. I did end up contacting Torsen with my questions. They basically told me that the 07 is equipped with a t-2 torsen diff which is very forgiving when it comes to oil. It doesn't require any specific oil or friction modifiers. I tried to get a specific oil recommendation from them, but they told me it was very difficult for them to recommend one brand over another because they use a lot of different oils and all of them are reliable in the t-2. I guess this means if I do buy the big ridiculous drum of go extra-s I'd use it 1 quart faster than people just using it for their trans, but I'll still probably skip it. I'm thinking of going with conventional Valvoline for the trans and mobil one for the diff.

Hopefully some time in the future someone will be searching this forum and find this thread to be useful. I think it's the only place on the net where you can actually find the proper oils for the 04-07 STI transmissions and diffs.

[XxSCAxX]

you can use the valvoline for the rear diff too.

[07STILimited]

Originally Posted by XxSCAxX

you can use the valvoline for the rear diff too.

Yeah I might just do that. I was thinking that since I can use whatever I want Mobil 1 might be a little better, but I'm open to suggestions with the rear diff. Torsen said I can basically use whatever I want as long as it meets the requirements.

[ogintheback]

Originally Posted by 07STILimited

I didn't think about the fact that the oil may break down over time. I just assumed that since it stays good in the car for quite a while it'd be fine in the drum. It would certainly take me years to use the whole drum though. Anyway, I believe the Torsen diff in the 07 uses crossed axis helical gears and does not contain any clutch. This is where I get confused. I thought that friction modifiers were only for clutch type diffs, but I'm not 100% sure. If I can't get the answer from Subaru my next idea is contacting JTEKT Torsen North America the makers of Torsen diffs. It seems silly that getting an answer from Subaru is so difficult. I'm assuming only they know what it is filled with at the factory.

Call Mastro in Tampa, they seem to be very knowledgeable and helpful.

[pearl boxer]

So from what I've read on this thread, I would be fine with running Motul Gear 300 in my 07 STI tranny and rear diff? There's really no point in me running the Motul PA 90 in my rear diff, seeing as it's not a mechanical style LSD, right?

That would be nice to just buy 5 or 6 liters of one type of gear oil.