From experience on my WRX the interval is every 30,000 miles. I have both the Impreza owner's and factory service manuals but I cannot find a maintenance schedule (which lays out how many miles the services should be done after).

In any case every 30,000 miles (for both the trans/front diff and rear diff) seems like it would be the appropriate time to do so. Even if you do it a little early it won't hurt.

The transmission and front differential are housed in the same unit so changing the transmission oil will in effect change the oil for both of them. You will need 3.5 Liters of 75w-90 gear oil. It must be rated as GL-5. I Highly recommend using Motul full synthetic gear oil. Great protection and longevity as well as ease of use when its freezing out. With other gear oils I have noticed that its harder to shift when first driving in cold temperatures, but with Motul it works good in all temps.

The rear differential must be serviced separately with the same type of oil as the trans/front differential. You need 0.8 Liters of 75w-90 (GL-5 rated). The rear differential is quite easy to drain and fill, I have got it done in less than 30 minutes. You will need some sort of fluid pump though, I recommend one like this Amazon.com: Slippery Pete Fluid Pump for Gallon Bottles and Wide Mouth Quart Bottles - Transfer Gear Oil, Transmission and Differential Fluid, Antifreeze with This 30cc Hand Pump: Automotive . You basically screw it on to the top of a bottle and just pump. You could also get an electric one which is quite convenient as well.

If you don't feel like waiting for the Motul to ship (even though its worth it) I could also recommend Royal Purple gear oil (which is available at AutoZone).

Lastly, get new gaskets where applicable. The transmission drain plug has a gasket (washer) that should be replaced. Depending on the type of rear differential your model has it may also require some washer. On my 2016 WRX it didn't, but I know that on others it may.

 

The schedule is in the separate 'warranty and maintenance' manual. For the manual transmission, it says to inspect every 30 months or 30k miles; never says replace. Says the same for the front and rear diff. Shorter intervals of course for 'severe' conditions. Unlike most manual service schedules, it includes replacing brake and clutch fluid every 30 months.

 

For the rear diff, use any quality hypoid (GL-5) lube you wish. (synthetic will improve MPG)

For the manual-Xmission/front diff (shared lube) It is HIGHLY recommended to use the Subaru EXTRA-S lubricant.

This is because of the 'shared' nature of the lubricant.

• The differential gears need hypoid lubricant (GL-5)
• The Xmission needs additives for the synchronizers to work properly (GL-4)

For many gear-oils, these two properties DO NOT come in the same lubricant.

• The sulfur/phosphorous additives for hypoid Extreme Pressure (GL-5) can wear down the synchronizers.
• The additives which aid the synchronizers to change gears smoothly (GL-4) need some 'grip' in the lubricant....which hypoid gears do not like.

Hence, Subaru has blended their "EXTRA-S" lubricant to meet BOTH of these demands within a single gearcase. It is not cheep... but you should only have to change it ONE TIME during the life of the vehicle.

Some folks have used other lubricants within the manual-Xmission/front diff... but the 'feel' of the shifting may get 'squishy' or 'notchy'. Also, gear-clash may be experienced on cold mornings.

If you are the kind of driver who does not care about the 'feel' of the shifting, nor about wearing out your synchronizers... use whatever lubricant you wish.

 

Yes I see they seem to have renamed it as high performance performance gear oil 75w-90.

Sale listing all seem to include a snapshot of a letter claiming it to be an alternative fluid to be used.

Amazon.com: Subaru 75W90 Extra S Gear & Transmission Fluid - 5 quart Bottles Sti Wrx Genuine SOA427V1700 X5 : Automotive

Buy Subaru 75W90 Extra S Gear & Transmission Fluid - 5 quart Bottles Sti Wrx Genuine SOA427V1700 X5: Transmission Fluids - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

www.amazon.com

For the manual-Xmission/front diff (shared lube) It is HIGHLY recommended to use the Subaru EXTRA-S lubricant.

This is because of the 'shared' nature of the lubricant.

• The differential gears need hypoid lubricant (GL-5)
• The Xmission needs additives for the synchronizers to work properly (GL-4)

Seeing this from above in the post, just has me cautious about what fluid I eventually purchase.

 

Did my first change over the weekend with 36k on the odo.
Used Motul 300 75w90 for both the tranny and rear diff.
Shifting does feel like it takes a little more effort but I kind of like that it has a more positive feel.

 

Yes i noticed the same thing. But once the oil warms up it should feel nice and engaging. Its good you did it. Now you have piece of mind for another 30k miles.

On a side note, doesnt diff oil smell like the worst thing ever???

 

That fluid definitely is definitely smelly, Not sure why that is. My damn garage smells like it now lol.
I don't know why the maintenance schedule only says inspect every 60k mi, then again I don't baby my car.

 

Severe duty for the differentials will be roughly 24k miles. I make it standard habit to do my brake fluid, differentials, trans (CVT, Auto or Manual) every 30k. I just recently posted an OEM fluid chart in the maintenance page, so feel free to check that out. Subaru offers a 75W-80 GL5, but only in 5 gallon jugs, so I went aftermarket and did Motul 75W-80. You can also use a 75W-90 but may see a decrease in economy, but likely not enough to justify any changes.

 

How is the shifting and performance of the transmission with Motul 75W80? Are you happy with it? It’s the only fluid I can find that’s both GL4 and GL5 specified. Probably as close to EXTRA MT as you can get in an aftermarket oil.

 

So if the Extra-S only comes in 5 gallon jugs, and I need a couple quarts (if that) for the manual transmission, what aftermarket fluid actually meets the properties of having GL-4 and GL-5?

 

From my understanding, Extra-S is no longer manufactured or has been rebranded to something else. Any of your well known gear oils will likely meet the GL5 API requirement for these cars. GL4 is likely not a fluid that we would use since the front diff and transmission cavity are the same. GL5 is very common (Valvoline, OE, Mobil, Motul, AMSOIL, Redline, etc.). GL4 is a little harder to come by but likely not needed for the Impreza since its AWD. But look into any of those brands and make sure its synthetic and you should be fine. No LSD in these cars to need to worry about friction modifiers.

 

Thanks for the info.

Just curious now if the factory oil is 90 in the rear, then wouldn't sticking with 90 provide similar economy and not a decrease?
And that going to 80 may provide an increase in economy instead?

 

I can check at work tomorrow. You'd be surprised how often they change this stuff in the manual. I've found historically that the CVT models get Extra MT in the rear diff but the manual cars get 75W-90, which is very strange.

 

From the manual.

 

Booom, there ya go. Here is a screenshot from the service manual as well. If you want to max out efficiency, as stated you can do 75W-80 in both cavities. 75W-90 is also allowed.

 

I changed out my M Tranny and R Diff fluids last weekend to Motul 300 75w90 which is rated GL4/5. I think some other people on the forum have done the same. Although the owners manual did say that it could detract from economy and drivability the only difference I can feel is that shifts take slightly more effort. I kind of like that though.

 

I ran AMSOIL SG 75W-90 in my 17' 5MT and it felt fine as well.

 

yeah, the biggest power mod I've done is taking out the carbon filter. Car feels better imo.

 

Yeah I'm sure it helps a bit with throttle response. These engines are not designed for power, thats for sure lol.

 

I think the Impreza would be fine with the 2.5 from the Legacy. A little bigger and more power as opposed to going with a turbo. Just my opinion though. Don't get me wrong, turbos are nice. I have an S4 twin turbo but I didn't buy the Impreza to be a speed demon. If I was looking for that and wanted to stay with Subaru I would have gotten a WRX. Since this is an everyday car for me along with smoking cigars, I couldn't justify more money. Now my S4, that is a different story! One day I will fix it up and it will be better than ever. Until then, it just sits in the garage.

 

I think the 2.5 would also be a great option and likely even get better mileage with the gearing the car has. My personal recommendation would be to use the 1.6 or 1.8 turbo engines used in the Levorg overseas in the Impreza. I think it would offer more power, better mileage and a tuning aspect for people who want to tinker.

 

Good to know. Thanks!

 

I know this is an Impreza forum but I wanted to share some experience with Redline MT-90 which is a GL4 75W-90. I used it in both my old 95 Pathfinder MT and my old 2004 A4 MT. When it was below 30 degrees it absolutely sucked! The colder it was, the harder it was to shift until the MT warmed up. I was extremely surprised since this stuff was supposed to be good till -54. In colder temps it was like shifting through mud and sometimes the shifter would be frozen and have to be hit to break it look (by hand of course). I ended up getting rid of the Pathfinder with the Redline still in there. In the A4, I ended up going back to OEM fluid before I junked it.

 

I just purchased a preowned 2017 Impreza Sport 5 speed with 64,000 miles on the odo. I was lucky enough to buy it from the dealership that sold it originally and did all of the maint, so I know the drive line fluids were done at about 40,000 miles. However, the 5 speed is not shifting that well, very notchy and a bit sloppy, so I am going to change all the drive line oils. I am leaning toward Motul Gear 300 75w90 but a couple people here said it made shifts harder. I don't want that, but I do want a 100% synthetic, long lasting oil that also smooths out shifting a bit. Is there really a marked difference in feel between Motul 75w90 vs 75w80?

 

The OE Extra MT transmission fluid is 75w80 viscocity but is only sold in huge quantities. It’s a good idea to use 75w80 as a replacement even if it isn’t full synthetic, especially if you live anywhere with freezing winter temperatures. In Canada people have had transmisson damage by running 75w90 in the winter if you go by the service specifications, but to be fair, it’s stated that 75w90 will affect driveability.

 

75w90 does take slightly more effort, but as Winter is coming I'm afraid. If I had to do it again I'd prolly use Motylgear 75w80 for the front diff. Still use 75w90 on the back though

 

WHat is the difference between


I will probably go this route and use the lighter weight in the trans.

Does anyone when what is the difference between MotylGear 75w90 vs Motul Gear 300 75w90. I'm not sur which one to use in my 2017 Impreza Sport rear diff.

 

The only real difference that I can tell is that Gear 300 says it's 100% Ester based synthetic while the MotylGear 300 says it's "reinforced with synthetic base stocks"

 

Don't put too much faith in the "ester" base. I had redline MT-90 in my 95 Pathfinder and 2004 A4. Supposedly has a pour ping at -49F. In anything under 30 degrees I had a lot of trouble shifting. There were some times where I had to break the shifter free due to it being frozen. Now, I'm not saying the Motul isn't good but it might not be a bad idea to compare to the OEM stuff. It may be that the OEM stuff is synthetic just not ester or may contain some ester. Could be PEO based too. Now, I am just relaying my experience and with the trans only. For my diffs I used Amsoil and I can't say I noticed a difference between Amsoil and OEM. I just replaced because they were NEVER replaced.

 

75W-90 is fine. Motul sells 75W-80 GL-5, which is what I'm using now since AMSOIL doesn't make a 75W-80. No issues and felt fine in the winter.