Transmission Oil Comparison - Notes, Data, and Results

[Brock H.]

TLDR: Motul DCTF (and the stock LV 75W by association) is not acceptable for anything more than daily driving and possibly some spirited street driving. Oil broke down after 4 days of higher level AutoX events. I would suggest to use known/respected 75W90 weight Transmission Oil for any performance driving.

Preface: Got my BRZ in late 2021 and when I was waiting to receive the car, I noticed something in the user manual. For the 2022 BRZ, the only “recommended” transmission oil per the owner manual is GL4 SAE 75W or Low Viscosity (LV) 75W, which is a relatively rare fluid and is most likely there only for Fuel Economy standards.

For those that run our cars hard, the standard for the last gen has been good quality GL4 75W90, so 75W and its low viscosity variants seemed too thin for any sort of spirited driving. As such, I decided to test out a known 75W Low Viscosity Oil and compare to my old standard of Motul Gear 300 75W-90. This was originally intended to be a “Shifting Feel” focused test against a known quantity, but there was some scope creep (as is usual with any car project) due to some findings.

Results are as follows:

Fluids Specs:

· Stock - LV 75W (Assuming Toyota Spec) – Viscosity @ 100°C -> 6.3 ~ 6.7mm2/s – Unknown
· Baseline to Compare – Motul Gear 300 75W90 – Viscosity @ 100°C -> 14.2mm2/s – Full Synthetic
· Low Viscosity to Compare – Motul Multi DCTF – Viscosity @ 100°C -> 7.3mm2/s – Partial Synthetic
---Meets Toyota LV 75W per public Technical Data Sheet (TDS)

Stock LV 75W Notes:

· ~700 Miles, was only intended to be used as break-in oil
· Cold fluid feel was only present on the first couple of shifts. Was only slightly more resistant in comparison to the warmed-up fluid feel.
· Warmed Up feel was neutral, almost what I would call “non-descriptive”.
--- Force to get into gear was slightly on the light side. Not too light, nor did it require too much effort.
--- I would call the shifting feel relatively fluid. There was some notchy-ness if you weren’t accurate on the shift, but it was smooth overall.
· I didn’t feel any degradation of fluid, but it was during the break in period and I didn’t autocross with this fluid.

Motul Gear 300, 75W90 - Baseline:

· ~1350 Miles on the Fluid
· Cold fluid feel is quite a difference from the warmed-up feel. I would describe it as fluid but resistant. Like running a stick through honey or molasses (Not nearly as thick, but you get the idea).
· Warmed Up feel is great. Feel is fluid/smooth, tight, with some effort needed.
--- Best way to describe the force to get into gear was middling. Compared to the stock fluid, the Gear 300 requires what I would describe as a “commitment” to change gear rather than the “absentminded” shifting the stock fluid allowed. To me, the Gear 300 is satisfying to shift with.
--- Shifting feel is very smooth and fluid. Even inaccurate shifts were smooth and were guided to the correct position.
· MPG did drop by some amount. Average seems to have been between 1-2 MPG. 27-28 MPG highway was the usual.
· I didn’t feel any degradation of fluid with 4 AutoX events on the fluid. This was the same with the last gen.

Motul Multi DCFT - Comparison:

· ~700 Miles on the fluid
· Cold fluid feel was only present on the first couple of shifts. Like the stock fluid, it was only slightly more resistant in comparison to the warmed-up fluid feel.
· Warmed Up feel was light and smooth
--- Force to get into gear was relatively light. Comparable to the stock fluid
--- I would call the shifting feel very fluid and smooth. Just allowed for quick, smooth shifts. Gave a little feedback if your shift wasn’t accurate, but it wasn’t rough in that regard. Essentially, the feel kept the same qualities of the Gear 300, but was lighter in overall effort.
· MPG went back up by a large amount. Was at least a jump of 2 MPG. 29-31 MPG highway was the usual.
· Fluid was obviously degrading during the 2nd Regional AutoX event. Shifts had gotten quite notchy. Both events had my car sitting against redline in 2nd gear for a couple of seconds, and it seems to have overheated the liquid. It stank coming out, flowed almost thinner than water, and had turned grey from the amber it went in as.

Conclusion:
The Motul DCTF is most likely a very good stand in for the stock transmission fluid, but is in no way good for anything other than standard driving and maybe some spirited weekend runs. Feel was better than stock, and it kept the fuel efficiency up. However, keep in mind that the 75W90 weight isn't in Owners Manual and as such, Subaru can deny warranty if they so choose.

Note:
Redline MT-LV also meets the Low Viscosity (LV) 75W requirements, but was not tested. I didn’t have time to test it with all the other AutoX events I was wanting to make, and with knowing that the Motul DCTF didn’t work even for AutoX made me skip it in general. However, it is a fully synthetic oil and may fair better than the DCTF. Maybe a future test for someone else, but I will stick with 70W90.

[Brock H.]

Reserved for possible follow-ons:


Video of the DCTF Draining shows the how broken down the fluid is:

[LRNAD90]

I've always had positive experiences with Redline MTL products in both finicky Land Rover Manual boxes as well as Subaru Transaxle boxes. So I'd be curious how Redline Products stack up..

Redline doesn't have a recommendation for the 2022 cars on their site, but recommends MT-90 for 2020 cars (75W90 GL-4)..

Redline Manual Transmission Oil Line-up

[timurrrr]

Originally Posted by Brock H.

Video of the DCTF Draining shows the how broken down the fluid is:

Have you ever drained a brand new trans fluid to compare against?
I did, it flowed basically the same.

[DrinkenBRZ]

Originally Posted by timurrrr

Have you ever drained a brand new trans fluid to compare against?
I did, it flowed basically the same.

Yeah, the one uoa I’ve seen on the OEM LV was 7.7cst at 100c close to the RL DCT at 8.1 when it’s new and I’ve not seen RL shear much in use so I agree with you. The OEM LV starts around 9cst for reference. Redlines LV is around 7 new, so maybe too thin for these transmissions.

[OkieSnuffBox]

I'm curious why you would put in fluid designed for a DCT gearbox into a manual transmission?

[Brock H.]

Originally Posted by OkieSnuffBox

I'm curious why you would put in fluid designed for a DCT gearbox into a manual transmission?

Per my initial post, Motul Multi DCTF meets Toyota LV 75W per public Technical Data Sheet (TDS). It was tested because for the 2022 BRZ, the only “recommended” transmission oil per the owner manual is GL4 SAE 75W or Low Viscosity (LV) 75W. I wanted to test if a commonly found fluid that meet owner manual specs works for any spirited driving. In the case of DCTF, it does not.

[Brock H.]

Originally Posted by timurrrr

Have you ever drained a brand new trans fluid to compare against?
I did, it flowed basically the same.

I don't disagree, the point was that the fluid was breaking down after 4 days of autoX, and I took video of the change. The stock fluid I drained at 700mi was about this thin or slightly thinner if memory serves right.

Originally Posted by DrinkenBRZ

Yeah, the one uoa I’ve seen on the OEM LV was 7.7cst at 100c close to the RL DCT at 8.1 when it’s new and I’ve not seen RL shear much in use so I agree with you. The OEM LV starts around 9cst for reference. Redlines LV is around 7 new, so maybe too thin for these transmissions.

That was one of the reasons I didn't test the redline. I did not want to go thinner than what I could find on the stock 75W LV.

[Simmons]

I have 9k miles on my car and way over 200 autox runs, the transmission feels just as good as it did when I bought the car.

[CSG Mike]

Originally Posted by Simmons

I have 9k miles on my car and way over 200 autox runs, the transmission feels just as good as it did when I bought the car.

Feel good =/= fluid is in good condition.

You might be surprised when you drain the fluid! If your fluid looks great, you may have a wednesday transmission.

[dreamwonder]

I had my oem fill analyzed by Blackstone after 16 track days, it was bad. It was more grayish than what was in your video. Replaced with Motul 75w90, after 10 days looked much better, but can still see the grayish tint. Gonna try 8 days next and see how that plays out. 1 track day = 1.5hrs ish.

[Desertnate]

For those of us who use the car for both Autocross AND daily drive it in sub-freezing winter conditions, is the heavier transmission fluid even practical? I'd rather not have to wait several minutes for the car to warm up before it's drivable.

I remember as a kid my Dad's car in the 80's was impossible to shift until it warmed up. I'd rather not have to deal with that.

[Desertnate]

For those of us who use the car for both Autocross AND daily drive it in sub-freezing winter conditions, is the heavier transmission fluid even practical? I'd rather not have to wait several minutes for the car to warm up before it's drivable.

I remember as a kid my Dad's car in the 80's was impossible to shift until it warmed up. I'd rather not have to deal with that.

[Petah78]

Originally Posted by dreamwonder

I had my oem fill analyzed by Blackstone after 16 track days, it was bad. It was more grayish than what was in your video. Replaced with Motul 75w90, after 10 days looked much better, but can still see the grayish tint. Gonna try 8 days next and see how that plays out. 1 track day = 1.5hrs ish.

I am wondering if the greyish tint is a result of flushing out break in materials? I think i am going to drop the factory fill and put in amsoil 75W-90 as well.

Thanks.