Diff. gear oil for a 2023 forester what to use

[markc17]

I have a 2023 Forester and need to change the front and rear differentials gear oil. Subaru says to use SUBARU EXTRA MT oil in the front diff and to use a GL-5 in the rear one. Amsoil shows that they do not have one for the front diff, but their severe gear oil is ok for the rear one. I have used their severe gl-5 for a long time. Any thoughts.

Thanks Markc

 

[Rand]

You can use the amsoil in both might lose .1mpg.

otherwise (from memory) extra mt is a 70w80 GL-5 gear oil.
fairly exotic but a few others are available now.

The important part for the front is its GL-5 you can use the factory 70w80, or 75w80 75w85 75w90 as long as its gl-5.

I'd run the amsoil 75w90 with full confidence and a minuscule loss of MPG.

 

[slacktide_bitog]

Any GL5 will be fine in both. Any 75w90 GL5 will be fine, so just use the cheapest synthetic 75w90

Only the manual transmissions are picky, since they need GL4 for good shifting and GL5 for hypoid protection. The manual transmissions are combined with the front diff, while the automatic transmission is separate from the diff.

 

[tblt44]

Redline ?

 

[markc17]

Thanks for all the replies. Did some investigating and found that the Extra MT gear oil is made in Japan. It is a 75w/80 FE gear oil.
I believe that the FE stands for Fuel Efficient. It is made by MITASU Corp. in Japan. Seems like all of the auto companies are doing the same thing now, trying to get the best mileage out of their autos. CAFE standards and a selling point to the consumer. I think I will stay with Amsoil Severe Gear 75W/90. Been using that in my shaft drive motorcycle for 10 plus years.

Markc

 

[GW.]

I use 75W-90 front and rear.

 

[SubieRubyRoo]

I use 75W-90 front and rear.

Same.

 

[Nuclear_42]

Amsoil Signature 75w-90

 

[Rand]

When I change mine in the spring it will be getting 75w90 front and rear (probably HPL)

Although I have 1.5qts of motul gear 300 in the garage.. might be tempting me to be cheap.

 

[Delta]

Motul Gear 300 75w90 is a favorite amongst the Subaru community. I bought a 5 pack off Amazon for like $80 when I swapped out the rear diff and trans/diff oils on my WRX. Can't say I really felt too much of a difference besides 2nd gear being really notchy when it's cold out, but that doesn't apply to your Forester.

 

[4wd]

Using ASG 80W-90

 

[SubieRubyRoo]

Motul Gear 300 75w90 is a favorite amongst the Subaru community. I bought a 5 pack off Amazon for like $80 when I swapped out the rear diff and trans/diff oils on my WRX. Can't say I really felt too much of a difference besides 2nd gear being really notchy when it's cold out, but that doesn't apply to your Forester.

I’d been on that wagon for awhile but got off once I found HPL. While Gear 300 is great for the diffs, it’s definitely not the best for Subaru manual transmissions that see temps below freezing. I’m sure @High Performance Lubricants has a suitable lubricant that substitutes for Subaru Extra MT, which I believe is a 70w80? @HPL Plant Manager I think you guys have already created that lube?

I’ve never used Extra MT because I don’t put much weight in OEM fluids that are super expensive with no information about what makes the lubricant “special”.

I’ve also used both SVG that @Pablo reps, and HPL CC 75w90 in several Subaru AT diffs. There’s no discernible difference in performance, probably due to the fact that an AWD 2.5 NA boxer is only sending about 30hp per wheel, plus those fluids are capable of much higher performance than what my humble Pleiades is capable of sending its way

 

[ARCOgraphite]

Valvoline synthetic 75w-90 in the rear. Did it myself, took less than 1 juice bag. No more Drain and fill plugs on the rear cover, on the Crosstrek they are on the pass side of the housing. One is a hex head bolt (13mm?) the other a larger Torx IIRC. Forget the size. I haven't done the front combinde transmission up front yet. Car (the last MT-6) is shifting well and don't want to mess that up with some not to spec gear oil. - Arco

 

[Delta]

I’d been on that wagon for awhile but got off once I found HPL. While Gear 300 is great for the diffs, it’s definitely not the best for Subaru manual transmissions that see temps below freezing. I’m sure @High Performance Lubricants has a suitable lubricant that substitutes for Subaru Extra MT, which I believe is a 70w80? @HPL Plant Manager I think you guys have already created that lube?

I’ve never used Extra MT because I don’t put much weight in OEM fluids that are super expensive with no information about what makes the lubricant “special”.

I’ve also used both SVG that @Pablo reps, and HPL CC 75w90 in several Subaru AT diffs. There’s no discernible difference in performance, probably due to the fact that an AWD 2.5 NA boxer is only sending about 30hp per wheel, plus those fluids are capable of much higher performance than what my humble Pleiades is capable of sending its way

I'm probably gonna need a new transaxle here anyways. Previous owner didn't believe in fluid changes so the fluid was pretty dark. Now I'm getting some whine 1-3. Almost sounds like strait cut gears. Buy a used WRX they said.... it'll be fun they said....

 

[SubieRubyRoo]

I'm probably gonna need a new transaxle here anyways. Previous owner didn't believe in fluid changes so the fluid was pretty dark. Now I'm getting some whine 1-3. Almost sounds like strait cut gears. Buy a used WRX they said.... it'll be fun they said....

Depending on which fluid you choose, this may be a place where LiquiMoly MoS2 actually has a valid application. I would try it in the fluid you’ve got in there now (assuming you already changed it), and run it for a few thousand miles. Then, change to your next fluid and don’t add it. If it’s going to help, it will be during that short OCI.

However, the whine is probably because the PO kept his hand on the shifter the entire time, causing additional wear on the shift forks, pads, and synchros. Not sure if MoS2 will help that, but it’s worth a shot…

 

[Delta]

Depending on which fluid you choose, this may be a place where LiquiMoly MoS2 actually has a valid application. I would try it in the fluid you’ve got in there now (assuming you already changed it), and run it for a few thousand miles. Then, change to your next fluid and don’t add it. If it’s going to help, it will be during that short OCI.

However, the whine is probably because the PO kept his hand on the shifter the entire time, causing additional wear on the shift forks, pads, and synchros. Not sure if MoS2 will help that, but it’s worth a shot…

It was definitely a chicks car and they blew up the engine as well, so yea

I already knew what I was getting into. I did change the fluid out, but may do another change when it warms up again. It's easy enough.

 

[SubieRubyRoo]

It was definitely a chicks car and they blew up the engine as well, so yea

I already knew what I was getting into. I did change the fluid out, but may do another change when it warms up again. It's easy enough.

Oh dear. You’ve entered the Bermuda Triangle of the Twilight Zone with that purchase, I’m afraid. Best of luck…

 

[oilboy123]

One of those cases where the weight is not a big deal at all. I don't know why the MFGrs play those weird weight games. I would use the Amsoil 75w-90 without a second thought.

 

[Wheel366]

I had the front and rear diff fluid in my 18 Legacy replaced by a local shop that used 75W-90 all around. I purchased SVG 75W-90 for my 19 Impreza but haven't had it done yet but am going to use in both front and rear.

 

[RallyXaDSM]

One of those cases where the weight is not a big deal at all. I don't know why the MFGrs play those weird weight games. I would use the Amsoil 75w-90 without a second thought.

CAFE. They are incentivized to go as light as safely possible to get an easy ~1-3%> bump in fuel economy for official testing. They have specific fleet targets to hit for average fuel economy and average 5-year cost of fuel purchases (which can also be marketed as a reduced TCO). This blurb is from a late 2010 guidance letter to manufacturers related specifically to motor oil, but it's not hard to imagine this sort of guidance extends to the vehicles other lubricants which are outlined in the OM.