Did the dealership replace my 6MT gear oil with the correct type??
 

I was going through and filing my brz's maintenance paperwork today and while reviewing it, I noticed that the gear oil used for both the manual gearbox and rear differential was listed as the same item, quantity 3 for trans and 1 for the diff. The description is listed as Valvoline 75W90 synthetic.

From what I understand the torsen rear diff likes 75w90 LS type fluid while the trans is gl3 or gl4 but without the LS as that type of gear oil has sulphur which can corrode the synchros in thr long term.

I did a google search for valvoline 75w90 synthetic, which at first view seems to be a LS type oil that is compatible with GL4, but upon further review of the product info for it indicates that valvoline doesn't recommend it for any transmission with synchros, so nothing made in the past 60 years or so.

Is there another 75w90 that they may have used that might not be LS type, but then I would have to get the diff changed to LS type, or is the more likely conclusion is that the trans has LS type in it?

I have put in an initial call to the dealership about this but was just wondering what gear oils the dealership has put into other ft86 type cars.


Thanks!!

LS type fluid is not required for our LSD differential since it’s a helical type there is no clutch plates which is typically what the friction modifier or “LS” description is designated for (it won’t harm it to us LS type though).

Lots of people use mogul gear 300 for both the transmission and differential which is a 75w90 (non LS type) safe for our transmission and Hypoid differential gears.

I personally use redline mt90 in the transmission and redline 75w90 in the diff.

What the dealer filled with is probably fine for a daily driver (I assume they used bulk vendor supplied Valvoline non LS type non synthetic fluid), how does it shift? I personally would run a higher end fluid like Motul, Redline, Amsoil etc.. if you are doing any spirited driving but it will cost more.

I am pretty sure that what is in both the transmission and diff is LS type gear oil, as that's that google returns for "valvoline 75w90 synthetic".

No, this is incorrect. It just uses regular 75w90 gear oil.

I use Motul 300 in both my transmission and diff.

My Subaru dealership used 80w-90 for the diff and its been great no issues.
https://parts.subaru.com/p/Subaru__/...A427V1800.html

Pentosin MTF2 75w-80 in the trans, Motul 300 in the diff

+1 on the Subaru oil

About a year ago, my Subaru dealership put in OEM 80w instead of 75w. They told me that that's what's used in STi. All gear changes are great now, even in Michigan winters. So that's what I'll stick to next time.

For me, the key is to change the gears quickly before the rpms drop too much for proper engagement. Also, I don't wait till redline to shift into 2nd. My 2nd gear comes in at about 15mph. I also have a fraction-of-a-second overlap between clutch press & throttle lift-off, just to maintain the rpms for 2nd gear engagement.

Sent from a potato

Just as an update for this, i have had my local mechanic change the MT oil to Amsoil MTG 75W-90 synthetic GL-4 that i ordered direct from Amsoil's website.. So far i've noted the transmission makes less gear noise in the low gears (1 and 2), and a bit less resistance going from 1 to 2 when the oil is cold. It seems the syncro's are doing a better job as well, with the limited mileage i have put on it so far.