2019 Subaru Crosstrek 6MT transmission fluid

J

jigger

Joined
Dec 15, 2024
Messages
7
I have 2019 Crosstrek with the 6MT. Where I live, we get 40C to -40C temp. I drive mostly like an old man and I never use force when shifting.

Last summer, I replaced my MTF and rear diff with AMSOIL SEVERE GEAR® 75W-90. I wasn't sure and the fact that there was some anti-slip additive in the oil was a bit a cause for concern. I immediately noticed my fuel economy worsen from 6.5L/100Km to 7L/100Km. It got much worse in the cold.

As we got in to fall, I noticed a reluctance in downshifting from 3rd to 2nd. As it got colder, for the first 5 minutes of driving, it's nearly impossible to downshift from 3rd to 2nd without being almost completely stopped. Yesterday, at -14C, I got a grind when I did the problematic downshift. The car also feels a bit sluggish (might be in my head) but fuel economy is noticeably worse.

I browsed the forums last summer before choosing the oil but seems like a made a bad decision. The "safe" alternatives appears to be Redline 75w-90NS and 2nd Motul Motylgear 75w-80. Cold temps is definitively a factor. At the same time, on Redline's website, they recommend MTL 75W80 GL-4 which is not a GL-5.

The question: So now I'm more confused than ever. What should I use for the transmission specifically?

I'm tempted to also switch the rear diff and possibly go with AMSOIL SEVERE GEAR® 75W-85 for the rear diff as the viscosity for 40c, 100c is slightly lower and -40c is much much better. It's relatively cheap for me and easily obtainable.

There are multiple threads about this topic but for most of the recommendation, people don't always mention the car itself and the temperature of the environment.
PS: I'm a long time user of the forum but lost my account. I did search, I did read a bunch of threads from this forums and others, I did read a bunch of spec sheets. I'm throwing the towel hence the new thread.
 
Last edited:
you have to have gl-5. You cant use the redline MTL The redline recommender page is incorrect.

1734300568926.webp

Subaru front diff is shared with MT.

I had 3 of these transmissions or their close subaru cousins.
The motul gear 300 75w90 was the best but they didnt have lower viscosity options when I used it..
redline 75w90ns was good, If they had a 75w85ns etc in gl-5 I'm sure it would be good.

I would use the

MOTUL MOTYLGEAR 75W-80​

If you want thin

or the motul gear 300 75w90 which is an ester based premium product.
 
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slacktide_bitog said:
Motul Gear 300 75w90 is the only choice for a Subaru manual transmission.

Page 445 of the 2019 Crosstrek owner's manual says to use 75w90
Click to expand...
I wasn’t thrilled with the Gear 300 in subzero temps, and I’ve never used the Motylgear (even though I have a quart now). Knowing what I do now, I would try HPL’s 75w90 Cold Climate without LS, but since OP is quoting temps in Centigrade I doubt HPL is an option.

In that case I’d have to agree with the Motylgear crowd.
 
Not a direct reply - but I’m super curious where you live -40 to 40C (that’s like -40F to 105F for US folks) is a ridiculous temperature spread.
Where in the world is this ?
Click to expand...
Quebec.
We don't have many days of +40 and we don't have -40 every year.
 
Last edited:
Rand said:
you have to have gl-5. You cant use the redline MTL The redline recommender page is incorrect.

View attachment 254310
Subaru front diff is shared with MT.

I had 3 of these transmissions or their close subaru cousins.
The motul gear 300 75w90 was the best but they didnt have lower viscosity options when I used it..
redline 75w90ns was good, If they had a 75w85ns etc in gl-5 I'm sure it would be good.

I would use the

MOTUL MOTYLGEAR 75W-80​

If you want thin

or the motul gear 300 75w90 which is an ester based premium product.
Click to expand...
Yeah. I was weary about the GL-4.
I'm aiming for that one (MOTUL MOTYLGEAR 75W-80) because of the viscosity that matches the Subaru Extra MT. I'm still waiting for more comments because it is expensive (60$/L) vs Redline 75w-90NS at 38$/L.

Of all the positive comments for the thicker versions of motylgear, people tend to not mention the car they have and especially, the temperatures ranges they operate in or location. While, many mention worst performance in the cold with 75w-90 motul vs redline ns.
 
Red Line is my least favorite for finicky when cold manual transmissions, I had it in my VW and when it got 32f or below getting it into second was a real pain. Filled it Pentosin MTF2 (discontinued) and it was as easy as it was when it was warm. Her Subaru is selling the 75w-80 for these cars, it seems to work better in cold climates, for lower US states definitely use 75w90.

https://parts.subaru.com/p/Subaru_2019_Crosstrek-20L-6MT-Premium/49506107/soa748v0100.html
 
@jigger, welcome back!

I'm following this with interest. I've always thought that a GL-4 fluid is best for a manual transmission, as the sulphur additives in a GL-5 gear oil degrade the brass synchronizers ... but then wonder whether, in a FWD/AWD application, does a GL-4 fluid adequately protect the transaxle gears (that is, those gears that are equivalent to those in a RWD differential), where ideally a GL-5 fluid would be specified?

(This reminds me that back in the late 1970s a friend's Austin Mini had a shared sump (that is, motor oil and transaxle fluid together) that took 5 quarts of motor oil (presumably 10w30)).

And to confound things, I believe that a good MTF should have additives to make it "grabby", to get the synchronizers up to speed.

What does your owner's manual say? Does it specify GL-4, or GL-5?

Regardless, I recommend you should use a dedicated MTF, rated GL-4 or GL-5, depending on what Subaru specifies.

I look after a 2009 Mazda5 with MT, operated in the temperature extremes you face, and have been pleased with both Redline MT-90 75W-90 GL-4, and Pennzoil SynGear 75W-90 GL-4. The Pennzoil MTF was hard to find last time - it may have been discontinued.
 
Mazda and about 95% of other MTs are nothing like Subaru manuals. Using a true GL-4 will have you replacing that transmission in short order due to corrosion from the sulfur-based EPs. One can use a sulfur-free GL-4/GL-5 fluid, or GL-5 fluid, but NOT a GL-4 only fluid in Subaru transaxles because they have bronze hypoid gears.

It’s fuzzy because it’s been awhile, but IIRC we had another thread about this where @High Performance Lubricants said they would make the non-LS CC version in 75w85 I think??
 
Number_35 said:
@jigger, welcome back!

I'm following this with interest. I've always thought that a GL-4 fluid is best for a manual transmission, as the sulphur additives in a GL-5 gear oil degrade the brass synchronizers ... but then wonder whether, in a FWD/AWD application, does a GL-4 fluid adequately protect the transaxle gears (that is, those gears that are equivalent to those in a RWD differential), where ideally a GL-5 fluid would be specified?
Click to expand...
Gl-4 is plenty of protection unless you have hypoid gears which "transmissions" do not have.

The OP has a shared sump transmission with front differential that requires gl-5 for the differential part.
Number_35 said:
And to confound things, I believe that a good MTF should have additives to make it "grabby", to get the synchronizers up to speed.
What does your owner's manual say? Does it specify GL-4, or GL-5?
Click to expand...
Its not so much additives for a MT, but LACK of friction modifier additives which make it suitable for MT use.
Owners manual says GL-5 75w90.. however the OE extra MT is a gl-5 75w80
1734356450712.webp


All the fluids that were recommended in this thread were approved for transmission use.. for example the motul 75w80 states it on the bottle.
1734356781891.webp

https://www.summitracing.com/parts/mtl-105782
$60CAD/L seems steep the motul is $13 USD at summitracing.com
 
Motul gives viscosity in mm²/s units and not cSt (edit, both unit seem to be of similar value in conversion)

IIRC the Extra MT is ~44.5cSt at 40c and ~9.3cst at 100c. pp -42c (this is by memory so excuse the imprecision, can't find the source)
MMG 75w-80 is 58.8 mm²/s @ 40c and and 10.1 mm²/s at 100c. pp -36c
MMG 75w-85 is 82.6 mm²/s @ 40c and and 12.6 mm²/s at 100c pp -45c
AmsSG 75w-85 is 76.9cSt at 40c and 13.3cSt at 100c. pp -46c
AmsSG 75w-90 is 97.8cSt at 40c and 16cSt at 100c. pp -43c

Viscosity is much lower than the Amsoil I got in it atm and there's no anti-slip additive which I think might be one of the reasons for the reluctant downshifts. I see they have a 75w-85 as well that is GL-5. Interestingly, the 75w-80 pp is -36c while the 75w-85 is -45c.

I also found this from NASIOC forum for a user name plastic.wood: https://forums.nasioc.com/forums/showthread.php?t=2809891
I tried the motylgear 75w80 a week after changing the factory fill oil with the motul gear 300 oil. The car is a 2014 6mt outback. According to the manual, the factory fill was the extra mt oil. Shifting with the gear 300 oil wasn't smooth at all. That’s why I decided to try the motylgear 75w80. Shifting is now very similar to what it was with the factory fill. It’s considerably smoother than it was with the gear 300. It also smooth while cold; morning are still at 0C - 5C in april here in Quebec City.
Click to expand...

Looks like I'll try Motul motylgear 75w80. I'll buy enough to do the rear diff as well. I still have about 1.5L of Amsoil SG 75w-90 in case MMG is too thin for the rear diff (doubt it).

Thank you for the summitracing site. I'll check with a local shop see how much they charge and go with summit if it's way to high.
 
Last edited:
SubieRubyRoo said:
Mazda and about 95% of other MTs are nothing like Subaru manuals. Using a true GL-4 will have you replacing that transmission in short order due to corrosion from the sulfur-based EPs. One can use a sulfur-free GL-4/GL-5 fluid, or GL-5 fluid, but NOT a GL-4 only fluid in Subaru transaxles because they have bronze hypoid gears.

It’s fuzzy because it’s been awhile, but IIRC we had another thread about this where @High Performance Lubricants said they would make the non-LS CC version in 75w85 I think??
Click to expand...
I thought it was the other way around - that is, that GL-4 fluids didn't contain the sulfur additives that corrode the yellow-metal synchronizers.

@MolaKule, your input is requested.
 
If the factory subaru oil was doing fine, I would probably go back to that unless there's a specific fluid that's known to work on a subaru forum. Trying to figure out one that's "better" can take a long time as they don't publish the specs that matter for a mtx to work well?
 
IndyIan said:
If the factory subaru oil was doing fine, I would probably go back to that unless there's a specific fluid that's known to work on a subaru forum. Trying to figure out one that's "better" can take a long time as they don't publish the specs that matter for a mtx to work well?
Click to expand...
Hard to find. Have to buy in 5 gal bucket

I would use 75w90 in the rear. Not 75w80
 
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