GL4 vs Dual certified for manual trans (Toyota GR86)

A

altaylar

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Jun 20, 2025
Messages
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I currently use Redline MTL on my GR86`s MT, but looking to bumping it up to 75w90 for the next track season.

I`m debating the following 3 oils

Redline MT90 (GL4)
Redline 75w90 NS (GL-5, Redline says safe for synchros, has EP but no Friction Modifiers)
Motul 300 (GL4 and GL5 dual certified)

Have read quite a few in the forum, particularly @MolaKule `s posts (including the open letter), but most of them were at least a decade old, andI am curious to know what you all think.
 
If it is MT1 certified, it is probably safe for yellow metals.

However, MT specific fluids do tend to be more optimized for the friction modification needs of a MT gearbox.
 
I have the Motul Gear 300 in my WRX, and I can tell you below 40° it's very notchy until everything warms up. The first couple 1-2 shifts takes some paying attention.

After warming up, shifts pretty good. But, I'm probably gonna go with other options on the next change.
 
What do you hope to gain by bumping up to a 90 weight?
If you're concerned about wear, I would opt to shift from a GL-4 to a GL-5, but I can't see why you'd need to.
 
The 75w90NS and Motul are made for Subaru manual transmissions that are combined with a front diff for Subaru's AWD, but since the BRZ isn't AWD, there is no front diff, so instead just get a regular 75w90 GL4 if you want to go up in viscosity.

There is now another 75w90 GL4 option: Liqu-Moly Top Tec MTF 5400, part #22275

What does Subaru say to use? If the MTL is the correct type for your BRZ, stick with it.
 
Overfill said:
What do you hope to gain by bumping up to a 90 weight?
If you're concerned about wear, I would opt to shift from a GL-4 to a GL-5, but I can't see why you'd need to.
Click to expand...
On track fluid gets very hot, which increases chance of missing gear during fast shifting. So instead going from 4 to 5, you end up in 3, and your pistons go to Mars through the hood before Musk’s Space X. It is called “Money shift,” for a reason.
Thicker fluid will increase resistance and offer better feel where you are during shifting.
 
slacktide_bitog said:
The 75w90NS and Motul are made for Subaru manual transmissions that are combined with a front diff for Subaru's AWD, but since the BRZ isn't AWD, there is no front diff, so instead just get a regular 75w90 GL4 if you want to go up in viscosity.

There is now another 75w90 GL4 option: Liqu-Moly Top Tec MTF 5400, part #22275

What does Subaru say to use? If the MTL is the correct type for your BRZ, stick with it.
Click to expand...
For track, depending on gearbox, it matters a lot who makes fluid. I have Motul 300 Gear Power 75W80 and it is absolute gem of fluid. However, different gearboxes react differently to different fluids. His primary goal, I think, is to have decent accuracy and resistance when fluid is very hot. It is actually fairly big problem to find that.
Motul, Redline, Amsoil would be my go to to experiment which one is best. I know Porsche owners on track swear by Delvac 75W90. But again, each gearbox is different.
On track, manufacturer recommendations are irrelevant in this case.
 
altaylar said:
I currently use Redline MTL on my GR86`s MT, but looking to bumping it up to 75w90 for the next track season.

I`m debating the following 3 oils

Redline MT90 (GL4)
Redline 75w90 NS (GL-5, Redline says safe for synchros, has EP but no Friction Modifiers)
Motul 300 (GL4 and GL5 dual certified)

Have read quite a few in the forum, particularly @MolaKule `s posts (including the open letter), but most of them were at least a decade old, andI am curious to know what you all think.
Click to expand...
Have you looked at Royal Purple? I've used it in my differential and transmission in my 1984 RX-7 racecar.
 
Thank you all very much for all the comments!

As @edyvw said, i want a higher viscosity in order to compensate for higher temperatures track usage leads to. So i want to "bump up" the grade, and not necessarily the GL number. Though I would not mind that if NS fluid provides better feel shifting. And MTL started to feel like water after a 20 minute session, and with the grip upgrade I am planning, it will definitely get hotter and thinner.

@Pablo I might try Amsoil as well at some point. For now I would prefer to stick with redline or Motul for free replacements, but when that is gone, I think i will be big on Amsoil.
 
slacktide_bitog said:
The 75w90NS and Motul are made for Subaru manual transmissions that are combined with a front diff for Subaru's AWD, but since the BRZ isn't AWD, there is no front diff, so instead just get a regular 75w90 GL4 if you want to go up in viscosity.

There is now another 75w90 GL4 option: Liqu-Moly Top Tec MTF 5400, part #22275

What does Subaru say to use? If the MTL is the correct type for your BRZ, stick with it.
Click to expand...
Never thought about Liquimolly. That might be an option if i am unsatisfied with redline or Motul.

BRZ also specs MTLV, but i don't think that would be useful for track duty
 
altaylar said:
Never thought about Liquimolly. That might be an option if i am unsatisfied with redline or Motul.

BRZ also specs MTLV, but i don't think that would be useful for track duty
Click to expand...

The LM product is still fairly new.

Redline also offers MT-85 which is 75w85, so you can go a little thicker without going too heavy.
 
Motul motylgear or gear 300 get my vote for best shifting feel for a 90 weight. You didnt answer specifically, but im assuming from the context of your answers that you are concerned about the fluid getting too thin, but somehow not for wear's sake.
 
Overfill said:
Motul motylgear or gear 300 get my vote for best shifting feel for a 90 weight. You didnt answer specifically, but im assuming from the context of your answers that you are concerned about the fluid getting too thin, but somehow not for wear's sake.
Click to expand...
Yes the concern is high temp leading to thinner oil. I presume the feel and the protection goes hand in hand in that scenario, but go down fairly fast
 
Do you find the shifting quality is getting worse as it gets hotter?
Usually the viscosity is there to provide transport of the oil to the contact surfaces, and the AW/EP package to mitigate wear in boundary lubrication (gears and bearings). Synchro engagement is mixed, so viscosity and FM play a role in their behavior. As edyvw said, when the fluid is exceptionally hot, people easily money shift accidentally.
 
Overfill said:
Do you find the shifting quality is getting worse as it gets hotter?
Usually the viscosity is there to provide transmissionport of the oil to the contact surfaces, and the AW/EP package to mitigate wear in boundary lubrication (gears and bearings). Synchro engagement is mixed, so viscosity and FM play a role in their behavior. As edyvw said, when the fluid is exceptionally hot, people easily money shift accidentally.
Click to expand...
Yesh usually when you move the shifter vertically, there is a point where ai feel some level of resistance (engagement point). On the track with MTL there is no such thing, i moving from 4th gear, 3rd and 5th feels the same, as if synchros just greased.

i don't have a temperature gauge for the transmission oil, but if it.is that thin for the feedback, i presume it is too thin for protection too.
(And money shifting seems to be a real problem with this platform)
 
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