Originally Posted by Cdn17Sport6MT
To the OP, you might want to watch the embedded YouTube video by Redline. They do not speak about the MT-LV 70W-75 product, as that is the most recent one... but still, it is useful to listen to this info. Interesting, in that hinted-at within the video is a comment about Racers at times wanting to go to a bit heavier viscosity product for more gear tooth protection... so this echos what VW says, re the balance between synchro smoothness and overall balance-of-transmission-component longevity. Having said this, I would NOT stray from the Mfr's recommended SAE viscosity... nominally 75W (or, 70W-75... i.e. that is not a problem). I say this because, say, in the case of my Mazda - the speed-gears run on splined journals - with radially-fed oil holes... not on half-shell-caged needle bearings (like my Camry 5MT does). On the Mazda the shafting that has spine-type speed-gear journals is fed by an "oil-funnel" splash-lube trough system. Playing with a higher viscosity MTF could potentially negatively affect the ability of said system to properly lubricate the speed-gears with this design of oil delivery system. Not sure what the Aisin-Warner trans is like, in your Corolla. (Not 100% sure it is an Aisin-Warner... either). In any case Do Not play around with viscosities beyond what the Mfr. recommends!
https://www.redlineoil.com/mt-lv-70w75w
Cheers
The trade-off between protection and shift quality is an interesting one indeed and something I suspect may be a factor in this case. I guess we'll see - might take 5-10 years of otherwise trouble-free operation before I can conclude that.
. Now, if I do end up putting RL MT-LV in and the transmission fails after a few years, I'll never know for sure if I should blame Toyota or RL. Haha. Seriously, all I can do now is laugh. Frustrating.
It's not clear if it's an AW transmission. Toyota says it's their all-new design, but Toyota is so tightly linked to AW that it's likely AW.