GL5 and GL4 - 2023 BRZ Transmission and Differential

[AcceptableBanana1986]

I followed CSG’s recommendations:

Differential: 1.1 – 1.3 Liters of 75W90NS. After draining, fill until the fluid is dribbling out of the fill hole.
Be sure to use fresh washers for both the drain and fill bolts.
Torque Spec: 36.1 ft‐lb (49 Nm)

Transmission: 2.2 – 2.4 Liters total capacity. 1.1‐1.2L MT‐90, and 1.1‐1.2L 75W90NS. The objective here
is to use a 50:50 mix of the two fluids. This results in superior feel and protection, compared to straight
MT‐90. Crush washers are not used, as the transmission uses a permanent gasket.

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CounterSpaceGarage (CSG) recommends that I run a mix of GL5 and GL4 in the transmission (which calls for GL4) and GL5 solely in the differential. Will this be an issue in my transmission? I just find it strange that they recommend blending both. Hoping it won’t be as I ran it last year and had some 2nd gear lockout issues when cold (live in New England) but that’s about it.

 

[NibbanaBanana]

From what I've read here some gear boxes use brass and bronze parts. They call for GL4 lubes. GL5 could damage those metals. I've also read accounts of people using GL5 with no problems. I don't completely understand it so I won't.

My 2006 Chevy Aveo and the wife's 2013 Kia Rio call for 75-85 GL4. I emailed XOM and stated that my manual spec's 75-85 GL4 gear lube. Can I use their 75-90 GL5 synthetic M1 instead? They said no. No explanation given.

 

[martinq]

What's your use case? Are you racing?

If you're going to use Red Line in the transmission for winter I'd look at the MT-85 or MT-L, otherwise I'd look at Amsoil. What's the factory spec?

 

[AcceptableBanana1986]

What's your use case? Are you racing?

If you're going to use Red Line in the transmission for winter I'd look at the MT-85 or MT-L, otherwise I'd look at Amsoil. What's the factory spec?

Oh good question. Yes I’m autocrossing it every weekend and maybe a track day every season. The season goes from April to November.

 

[Ruturaj]

I assume you also had a thread in gr86 forum.

75W90NS has only GL5 rating, that would be bad for yellow metals as stated (may be mild). I would rather use Motul Gear 300 which has dual rating of GL4 and GL5 if one wants GL5 rated fluid. In your use case GL4 rated fluids like ford motorcraft or just MT‐90 should be enough. You can even go lower on viscosity.

I tried Motul Gear power 75w80 which doesn't shift well when cold. I have Redline MTL and ford motorcraft to try next.

 

[martinq]

Oh good question. Yes I’m autocrossing it every weekend and maybe a track day every season. The season goes from April to November.

In that case I'd recommend trying MT90 for the track season and MTL for the winter and go from there. I would also consider the Amsoil options depending on cost/availability.

 

[AcceptableBanana1986]

In that case I'd recommend trying MT90 for the track season and MTL for the winter and go from there. I would also consider the Amsoil options depending on cost/availability.

They got back to me from Redline.

The MT-90 is a GL-4 product that is safe for brass and fiber synchro’s. The 75W-90NS GL-5 is safe for brass synchro’s because it lacks the reactive sulfurs that can cause issues with yellow. Although they are both suitable for synchro’s mixing them would not be recommended.

 

[Asterix]

It's worth a try. I've used MT-90 in my old Supra W58 for decades with excellent results, cold and hot. I've never heard of mixing anything with it, but it should be harmless.

Yes, everyone, the Redline 75W90NS has no sulfur-based friction modifiers in it, unlike almost every other GL5 oil on the shelf. That's what the NS gets you (or doesn't get you, actually).

 

[burbguy82]

You could try Royal Purple Synchromax or 75w90 Maxgear.

Use it for a while, and then post a UOA to show how well or bad it does.