So 2017+ models CAN use GL-5 fluids in the tranny...
 

I want to change my transmission fluid so I started to do my homework on this and went through countless transmission fluid threads of recommendations and people warning against using GL-5... but they were all pre-2017.

An AMSOIL rep (through a clerk at an auto store) insisted that the AMSOIL 75W90 Severe Gear GL-5 will work for my BRZ and will not let me special order their regular manual transmission fluid.

I was going through my owner's manual and this was stated under Manual Transmission, "Other gear oil that meets APL GL-3, GL-4, or GL-5 and SAE 75W-90 specifications."

So... I guess Subaru updated the '17+ transmission to allow for GL-5 usage now?

I guess? Been using it in mine for a while now

Interesting. Seems kinda sketch. The transmission hasn't changed at all.

Not arguing with the manual but I'd stick with GL-4.

Personally, I'd go by what the book recommends (look in your manual). Not sure if there is an update, but definitely haven't read about one.


Also, I wouldn't trust the clerk at an auto parts store.

Kind of like when manufacturers change nothing in a transmission, but yet suddenly one year it's now "filled for life"..

Subaru only has GL-5 now as their OEM manual transmission fluid.
I emailed Subaru of America several times to confirm that it's OK to use Subaru OEM oil that states GL-5.

Is there a chance that the customer support guy didn't know what he was talking about? Possible! But when in doubt, Red Line is always there for you!

Sent from a potato

Last generation GL5 transmission fluids have additives that protect yellow parts of the gearbox thus even when manufacturers say only GL4 a GL5 oil can be used, for example Gear 300 IS GL5 but protects yellow gearbox parts that ask for <GL4

This article has been cited in the past plenty of times, but is still an excellent explanation of why GL5 ratings are NOT compatible for transmissions using brass syncronizers...nor are they meant to be. Written by a knowledgeable regular over at BITOG, in this case for the Corvair community. Brass is still brass though, regardless of it being in a '65 Corvair or a '15 Toyota...

https://www.widman.biz/uploads/Transaxle_oil.pdf

So what that tells me is Subaru decided it was cheaper to only keep GL5 around, so they re-specified the transmission to take GL5 for supply chain purposes. I doubt the transmission was actually changed in any way.

Not sure about that... but for my next change, I'm thinking of going with GL4... and might even add some ZDDP additive.

Sent from a potato