Amsoil and Lucas are my current go tos. I just did my diffs with lucas.

I won't speak to weight. But I've tried to stick to OEM requirements for the most part. Heavier oil can be good for really sticking in place but it comes at the cost of being easy to aerate.

 

I haven't looked into Lucas but will now. Definitely want to stick with OEM weight for year round usability.

So I just learned that the now conveniently discontinued Extra S god of gear oil isn't a full synthetic. Perhaps that's the key. There's a company Lubrication Engineers that's popular with the S2000 crowd that makes a semi synthetic (703). Expensive as shit but if it works it'll be worth it.

 

I've tried Motul in my 2002 gearbox only because I got it on sale but it turns out after all that I do love it in the gearbox. It's very dear though -- but if you are doing track days then you're spending money anyway so it might be worth the gamble to you.

 

Good to hear on the Motul. Do you remember which one it is exactly?

Gear 300 is very popular and often recommended, but many say it gets notchy and performance degrades, and issues like grinding return.

I think I found the right oil though. It's Motul, but the Motylgear Semi Synthetic 75W-90. Read nothing but good about it. Plus it's not insanely expensive like all the other boutique oils I came across.

Seems these transmissions prefer semi synthetic fluid, which is why Extra S was hailed as king. People report the Motylgear feeling even better than that, so I think we got a winner. Plus the Motul and Subaru link makes me happy using it.

 

Sorry I don't recall which one. I should probably change it soon too, come to think of it.

Oh! There is a difference between gearboxes you should be aware of though! If you have a 6-speed, and it's like the STi 6-speed in design, then it's pumped rather than a splash system. My 5-speed is a splash system.

If you've got a 6, be really careful what you put in there to make sure it's compatible. Go by the book strictly and consult other users with your exact setup -- I do NOT want to misguide you or future readers.

 

You also want to get a fluid that has the correct additives (friction modifiers), if the gearbox or rear differential require it. If you use the OEM fluid, then you do not have to guess. If you find an alternative, then do that last check before you buy it.

 

Good point. For the 5MT you do not want any friction modifiers ('LS' version) and the Motylgear does not contain any so it's perfectly suited. I've even read guys running these in the STi 6MT with success, which AFAIK do not require an 'LS' oil.

 

Not sure if there's a big difference between the 5MT & 6MT but I had good luck with subaru oil (Idemitsu) and Liqui-moly mos2 additive. The rough shifting has reduced a bit.

 

Yea me neither but I get the feeling it's significant, at least in terms of what fluids work best.

So going back to the drawing board lol. Came across some posts where people complain about the Motylgear.

Which leaves me with two semi-synthetic options really - Ravenol or Fuchs. I'm leaning towards the Fuchs. Popular with the Porsche crowd. Cheaper. Can't find anything negative (yet). Not much at all on the Ravenol. Don't want to be a guinea pig, but at the same time I do

May go with the Fuchs and see how it goes. If I don't like it, it's cheap enough to dump and try Ravenol without hurting the wallet too much.

 

Lol good luck and post your impressions. The oil selection is always a compromise because the diffs and synchros share oil. EP additives help diff but make synchros slip and vice versa.

I think most other true awd systems with center diff like longitudinal engine quattro have separate transfer cases and separate oils for diff and gearbox. Majority are wet clutch/haldex anyway.

 

Don't think brutally hard on this. It's easy to overthink it.

Make sure it fits OEM specs and it's from a reputable brand. Gear oil does get worked hard, but nothing like engine oil. The only times you've really got to be overly diligent is when you are doing diffs with clutch pads or that require certain friction modifiers.

 

Lol yea I'm having to catch myself and reel it back because this is starting to drive me crazy. Seems these Subaru transmissions are pickier than most, but the huge variance in people's experiences makes me realize I just have to see for myself. The condition of the trans seems to play a role too.

Anyway I'll see tomorrow what I can get the cheapest/quickest and will post an update.

 

@SD_GR Thanks for the tip. I've been doing so much reading that in the process I learned that from late 07 the STi 6MT no longer used a pump. They switched to scrapers for cost cutting.

I guess thankfully (but not really) I don't have to worry about that since I have a WRX with the factory 5MT. I've narrowed it down to semi synthetic fluids, and either Fuchs, Ravenol, or Shell Spirax.

The latter is basically unobtanium, or if I can get it at least double the cost of the Fuchs. The godly Extra S was made by a Japanese company Showa Shell Sekiyu, a subsidiary of Shell, that have since been bought by Idemitsu. I suspect one of the Spirax S4/5/6 variants will be the closest to it, or maybe even it. Whether I want to take that journey and figure all that out driving myself crazy in the process is another story. But I'm tempted. For science!

 

I just had my trans/rear diff serviced. (2013 5spd) I'm using Motul Gear 300 75/90 LS in the transmission and 90PA in the rear diff. I noticed that the drivetrain noise was a little less when I switched over to the Motul, but maybe it's just me. I haven't noticed any degradation, but I swap it out every two years. I do track the car a couple times a yea, but not drag racing or anything like that.

 

Did you do the change yourself? From everything I've read you're not supposed to use the 'LS' (Limited Slip variants with friction modifiers) in our transmissions. Have you ran it before? Any issues with grinding?

Yea there's sometimes a placebo effect. I realized it helps to not drive the car for a week or two. Can notice differences pretty easily then.

 

No issues at all. I started using it a couple of years ago, and just swapped out all the fluids again.

If you could drop a link to anything that talks about the fluid not being good for the five-speed, I'd certainly take a look at it. I couldn't find anything on the Motul site that cautions against using it. And the speed shops that I work with for my maintenance don't seem to have a problem with it.

 

Unless you have aftermarket LSDs installed the WRX uses open diffs front and rear so a limited slip specific fluid is unnecessary. In fact it can be too slick for the synchros, hindering proper engagement.

Don't have a single link that explains all this but a Google search will net good results. I checked Motul's site and using their 'Oil Selector' it doesn't list the 'LS' variant for the 5MT or 6MT.

 

Cool, I actually just sent an email to Motul to see if I can get some clarification. If it's bad for my car I'm going to take it out, no question.

When I read the product description on their website, while it may not be identified as the OEM style replacement, that doesn't necessarily mean that it's bad for the transmission.

I'll share what I hear back, and thanks.

 

So I have a 2015 WRX with the 2016 STI transmissions swap. I've always loved Motul 300 in the subaru transmissions or the Extra S. I honestly think Motul is better. also have had good luck with the Amsoil gear oil but i have only used it in the rear end. I had some grind after my STI swap from 3-4 under high acceleration. Swapped the Fluid to Motul 300, it helped a little. So i decided to try Redline lightweight Shockproof after a few thousand miles as the gear grind was really starting to bother me.
I was kinda skeptical. Some say that just adding a quart to the regular Fluid does wonders and others say just to run it straight. I decided to just run straight lightweight Shockproof, and let me tell you this stuff is MAGIC. The transmission has never shifted so smooth in and out of gear and no grind whatsoever now. Many guys running over 800whp on the stock transmissions swear by the stuff. the "Andrewtech Cocktail" is also popular. I have yet to see a single person complain about the redline lightweight shockproof after they tried it.

 

Thanks for sharing your experience. Interesting you liked the Motul better than the infallible Extra S. I had come across Shockproof too and was dead set on using it, as I read what you experienced about it being phenomenal. But I've been doing so much reading I can't remember why I wrote it off. I think people said the improvement didn't last long and performance degraded shortly thereafter? How many miles have you been running it?

You also have a STi 6MT which is significantly different than the 5MT from what I've read in terms of fluid compatibility. I may take a look at it again though because I'm having a hard time sourcing these other oils I've got my heart set on right now.

 

I use amsiol oil and motul gear 300 in my 2017 limited wingless rear and trans only didn’t use amsoil cause it wasn’t recommended on amsoil site I mean I used amsiol in the 2 evos I had and focus st and had no problems but I do think that motul works good I change it every 2 years or 12k miles usually it’s 2 years

 

A long-winded update for anyone interested:

Really struggled to find a semi synthetic 75W-90, as I was convinced this was best for these Aisin transmissions. Extra S was a semi synthetic and hailed as the best.

All the popular synthetics had some bad reviews. Went through all the (limited) semi synthetic, non-LS options. Made it all the way to the stuff Porsche guys run since some of their transaxles are made by Aisin; Shell Spirax S5 or Mobil Mobilube PTX. Factory spec'd oil. Very difficult to find. Porsche sells it under their Part #'s and used to disclose what it was, but after superseding the numbers no longer does. A lot of speculation and misinformation on forums, mostly stemming from dealer assumptions.

Porsche has Part #'s for 1L and 20L containers, and a few Porsche shops figured out which 20L one pertains to PTX, or more likely, saw the name written on Mobil's container they received for the respective Part #. Individual liters sell at a premium of $200 for five to my door. Or... I could source a 20L container from UK for "not much more". Use what I need and sell/store the rest.

Realized I was nuts, so back to square one to go over my options again. Found Eneos makes (made) one that would be perfect. NAPA had a great deal on 5qts for under $60. When I saw the bottles, noticed the manufacture date; three 8 years old and two 5. Clearly long discontinued and unusable. Returned them.

Set out to find out what the 1L Porsche Part #'s are for the Spirax or PTX because at this point I had my heart set on it and it's the cheapest option. Got Porsche Transmission Oil Part # 000-043-305-49 (suspected Spirax). Emailed Porsche Germany to get confirmation. All they'd say is it's made by Shell AG. That was good enough for me. This was most likely S5 ATE, because it's the only one of the Spirax line spec'd for cars and transaxles, and the only one "Approved by Porsche and Ferrari for transaxles".

Now that I have the Part #, where to buy. Most places in the states were expensive. More or less $200 shipped. More searching led me to a shop called Rose Passion in France. I know, but not only are they legit, they're well known in the Porsche community. Got 5L for $140 landed within a few days. Only ended up needing 4L.

What I found with most oils, and the reason I passed on them even though cheaper and easier to obtain, is viscosity at 40°C. Most are quite viscous, close to or over 100 cSt. Including the Mobil Delvac I was running, also popular among the Porsche crowd, but moreso for track use since it's factory fill in their GT3 cars. In colder temps, like what we've been having lately, it was super notchy and crunchy. Also, after working through the gears a lot and getting the trans hot, it almost felt non-existent, like it wasn't there anymore and there was metal on metal contact. Felt horrible. Although it always went into gear, there was some resistance which made shifts slower, making shifting less smooth.

The trans drain plug did have a good amount of gunk on it. More than I would've thought for the just over 15k miles run. Less so on the diff plug. Fluid appeared cloudy and pretty dark especially out of the diff.

Posting this update a bit prematurely as I haven't put a lot of miles on it but can say there's an immediate difference. The crunch that would especially happen in 1st and 3rd is gone. Doesn't feel 'dry' like before and more 'cushioned'. This Spirax S5 ATE has a 40°C viscosity of 81 cSt. Delvac is 120 cSt and a full synthetic, which seem to degrade quickly. No wonder it started feeling bad and sucked in colder temps.

I overthink and geek out on stuff like this so take it how you will. Not expecting this to become the next best thing but if it helps someone down the road I'd be happy. Also if someone wants a sealed 1L bottle lmk

TL;DR: Ended up going with Porsche Transmission Oil Part # 000-043-305-49. Semi synthetic. Porsche Germany confirmed it's made by Shell, which is most likely Spirax S5 ATE. Huge improvement. Feels great so far with no crunch and smoother, faster shifts.

 

This is interesting info and quite a lot of work for the oil. The low temp viscosity explains some problems. Mos2 helped but still has sandpaper shifts when cold and randomly sometimes.