Choosing transmission fluid for manual GR86 / BRZ

[Ruturaj]

I own a 2023 BRZ and been meaning to change manual transmission fluid.

On one hand, the transmission is mostly same from previous generation which recommended 75W90, but this generations manual recommends 75W.
And on other hand, Toyota's manual says lower viscosity oil was adopted (adding screenshot), I am not sure if that means mechanical changes were done that somehow would have negative effect on thicker oil, making thinner oil preferable.

The transmission is TL70 based on AZ6.

I gathered viscosity number of fluids people used in previous gen and feedback people had about them. Just for simplicity purpose I am adding options from redline. Few members used options from Pentosin or AMSOIL which in viscosity was similar to one of these options and that didn't get me much further.

I also heard argument that lower viscosity is due to EPA only and would cause more wear.

Other data I could find was extreme temperatures someone saw on track (as high as 147°C).

	Vis @ 40°C, CSt	Vis @ 100°C, CSt
Toyota LV 75W MT	30	5.7
Redline MT-LV 70W/75W	29.8	6.5
Redline MTL 75W80	50.8	10.4
Redline MT-85 75W85	62	12
Redline MT-90 75W90	82	15.5

Which oil should one pick? Based on previous gen's recommendation? Current gen's manual? Somewhere in between? Should it depend on use? Temperature range?

I am in PNW and I track car 6-8 times a year. I am not aggressive driver. But I would still be interested in why would one choose higher or lower viscosity. I put 3-5k miles on car a year and I am planning to change MTF every year.

 

[Rand]

The only modern subaru manual transmission that doesnt need or require GL-5 eh?

 

[Ruturaj]

The only modern subaru manual transmission that doesnt need or require GL-5 eh?

Yes, asks for GL-4 only. Seems like it's better to avoid GL-5 for this transmission from comments I saw.

 

[Rand]

Yes, asks for GL-4 only. Seems like it's better to avoid GL-5 for this transmission from comments I saw.

if you look at the 40 and 100c viscosities I would try the mtl 75w80

75w90 would likely be ok on track days but if you took it out even in a milder winter it wont be great for shifting cold.

 

[Number_35]

if you look at the 40 and 100c viscosities I would try the mtl 75w80

75w90 would likely be ok on track days but if you took it out even in a milder winter it wont be great for shifting cold.

For what it's worth, I ran our Mazda5 with Redline MT-90 in the MT and it was fine even on the coldest of winter days.

 

[Rand]

For what it's worth, I ran our Mazda5 with Redline MT-90 in the MT and it was fine even on the coldest of winter days.

I ran 75w90ns (gl-5) which isnt wanted in this application
in a 2011 forester 2013 outback and 2015 forester.
of course back then not much lower viscosity was available for gl-5.
Motul gear 300 shifted better when cold and it wasnt thinner.

The mtl 75w80 is close to twice as thick as the OEM fluid.. no reason to go 3x IMO.

 

[Ruturaj]

I ran 75w90ns (gl-5) which isnt wanted in this application
in a 2011 forester 2013 outback and 2015 forester.
of course back then not much lower viscosity was available for gl-5.
Motul gear 300 shifted better when cold and it wasnt thinner.

The mtl 75w80 is close to twice as thick as the OEM fluid.. no reason to go 3x IMO.

My dilemma is that if transmission if actually designed for 75W90 as 1st gen manual recommended and 2nd gen solely recommends it because of EPA then I would be running a fluid 2/3rd thicker.

 

[slacktide_bitog]

Be glad you don't need 75w90, as MT-friendly 75w90 basically doesn't exist in the US anymore

Thinner MT-suitable fluids are more widely available.

If you want something that's thicker than 75w but not as thick as 75w90, you can use Pennzoil or Valvoline Synchromesh, each around 9 cst; or you can use Royal Purple Synchromax (around 7.5 Cst)

Here is a more comprehensive list

The only modern subaru manual transmission that doesnt need or require GL-5 eh?

It's the only modern Subaru that doesn't share the manual transmission with a front diff (since it's RWD)

FWD and AWD Subaru manual transmissions are combined with the front diff and use the same oil for both, hence the unique requirements and being so picky with oil.

 

[MolaKule]

I think you would be ok with either the Amsoil MTF or the Redline MTL 75W80, both about 10cSt@100C.

 

[Ruturaj]

I think you would be ok with either the Amsoil MTF or the Redline MTL 75W80, both about 10cSt@100C.

I also looked at your big list.
Is MOTUL GEAR POWER 75W-80 new? It wasn't on the list and is about 10.5cSt@100C.

Edit: This seems to be super new https://new.motul.com/products/34781?product=MOTUL+GEAR+POWER+75W-80
Edit: Seems like not for US market yet

 

[edyvw]

I also looked at your big list.
Is MOTUL GEAR POWER 75W-80 new? It wasn't on the list and is about 10.5cSt@100C.

Edit: This seems to be super new https://new.motul.com/products/34781?product=MOTUL+GEAR+POWER+75W-80

I use in BMW Redline D4 and work excellent on the street, track, skiing etc. Not sure how it would behave in Subaru, but in BMW's with a manual it is probably most common among enthusiasts.

 

[Ruturaj]

I use in BMW Redline D4 and work excellent on the street, track, skiing etc. Not sure how it would behave in Subaru, but in BMW's with a manual it is probably most common among enthusiasts.

Are you sure it wasn't MOTUL MOTYLGEAR 75W-80? Which is synthetic blend. MOTUL GEAR POWER 75W-80 seems to be new or available in very few countries.

 

[edyvw]

Are you sure it wasn't MOTUL MOTYLGEAR 75W-80? Which is synthetic blend. MOTUL GEAR POWER 75W-80 seems to be new or available in very few countries.

Nope, Redline D4 ATF. I am sure, I filled it.

 

[Ruturaj]

Nope, Redline D4 ATF. I am sure, I filled it.

My bad, since you replied to that comment, I guess I was still in zone and thought you were talking about Motul gear. I will take a look at redline D4 ATF.

 

[Number_35]

I ran 75w90ns (gl-5) which isnt wanted in this application
in a 2011 forester 2013 outback and 2015 forester.
of course back then not much lower viscosity was available for gl-5.
Motul gear 300 shifted better when cold and it wasnt thinner.

The mtl 75w80 is close to twice as thick as the OEM fluid.. no reason to go 3x IMO.

I'm afraid to use a GL-5 gear oil in a manual transmission, even if the MT is rated for GL-5 or the fluid is rated GL-4/5.

In the FSM for our Mazda5, GL-5 is permitted depending on the VIN. Only GL-4 is to be used if the VIN indicates an early build. (Presumably Mazda hardened the synchronizers or something after the corresponding build date.) Our VIN is such that GL-5 is approved, but I've stuck with GL-4 and have been pleased with the results. (GL-4 is still allowed after the GL-5-permissible build date.)

I've been pleased with both Redline MT-90 and Pennzoil Syngear GL-4 MTF.

 

[Number_35]

This discussion reminds of an oddity regarding MTF; in the late '70s, a friend drove an Austin Mini, 1970ish, as his commuter car. He told me that the engine and transaxle shared a common sump which held 5 quarts (Imperial, so around 6 U.S. quarts) of 10W-30 motor oil.

 

[MolaKule]

I also looked at your big list.
Is MOTUL GEAR POWER 75W-80 new? It wasn't on the list and is about 10.5cSt@100C.

Edit: This seems to be super new https://new.motul.com/products/34781?product=MOTUL+GEAR+POWER+75W-80
Edit: Seems like not for US market yet

When I am notified of an MT fluid I verify the Oil Properties and application before I put it on my list, no matter where in the world its produced.

Let me state this again: Before changing an MTF in a vehicle, obtain an OEM fluid sample and post the analysis in

Gear & Transmission Used/Virgin Oil Analysis

Virgin and Used Gear & Transmission Analysis reports.

bobistheoilguy.com

so we can attempt to suggest a fluid of similar viscosity and additive signature. This removes a lot of guesswork on your part.

 

[Ruturaj]

When I am notified of an MT fluid I verify the Oil Properties and application before I put it on my list, no matter where in the world its produced.

Let me state this again: Before changing an MTF in a vehicle, obtain an OEM fluid sample and post the analysis in

Gear & Transmission Used/Virgin Oil Analysis

Virgin and Used Gear & Transmission Analysis reports.

bobistheoilguy.com

so we can attempt to suggest a fluid of similar viscosity and additive signature. This removes a lot of guesswork on your part.

Thank you. I emailed Motul asking about availability and they said it will be available in fall. I would very happy to contribute. For now I have ordered Redline MTL.