Originally Posted by pleopard
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.
-- it seems that really what you need is a fluid with better cold viscometrics than what came with your car. I've been driving manual transmission vehicles for my entire life, and living in Canada (albeit not regularly as cold as where you are), I've had cold shifting issues with almost every car I've owned except my current Benz C300 (which shifts beautifully in extreme cold, almost unbelievable really). I've also driven many VW's which seem to shift well in cold temps also. And the main difference I can see across the German brands rather than everything else is the use of very high quality and very THIN gear oil for the transmission. Also, they tend to use fluids with the most stable viscometrics, in other words, fully synthetic fluids with great basestocks that don't thicken up as much as the temp really falls.
So what I would try and what I've had luck with in the past with my previous vehicles is to select the best synthetic fluid you can find and start trying them one by one until you find one that you like. Obviously you can't make up for shortcomings in the transmission design, but you can try to make it as good as it can be with the best fluid for the application and weather conditions.
Redline MT-LV looks to be a great choice. Castrol also has some fully synthetic 75W manual transmission fluids that are available in Europe (I'm sure for a price you can have them shipped over). By memory they are Castrol Syntrans FE 75W, and Castrol Syntrans B 75W.
You should look for the lowest Brookfield viscosity numbers for extreme cold performance, as well as lowest 40 C KV numbers. And don't worry about transmission failure, you will not cause any damage to your transmission. After all, it was already shipped with 75W fluid in it, so technically you're replacing it with another fluid of the same viscosity grade anyway (perhaps just thinner within the grade). Also, anecdotally, I can tell you that in previous transmissions that specified thicker fluid, I've used low viscosity fluids with great success and for hundreds of thousands of km's without issue or failure of any kind.
Good luck and let us know how it goes.
![[Linked Image]](https://www.bobistheoilguy.com/forums/attachments/usergals/2020/02/full-13492-41689-screenshot_20200225_204913_01.jpeg)
As you can see, all they specify is a min and max range for kinematic viscosity at 100 C for the non-W grades, and a min kinematic viscosity plus a min temperature that must be achieved before dynamic (Brookfield) viscosity rises above 150,000 cP for the W grades. Also, W grades can be combined with non-W grades and those resulting multi grades must meet both requirements. So those are the ranges.
But when looking at the W grades, the dynamic viscosity requirement is not very stringent. For example, a 75W must reach -40 C before it's dynamic viscosity exceeds 150,000 cP. But a high quality synthetic fluid would have a dynamic viscosity of much much less at the same temp.
Here is Pentosin MTF2 75W80 for example:
![[Linked Image]](https://www.bobistheoilguy.com/forums/attachments/usergals/2020/02/full-13492-41688-screenshot_20200225_205215_01.jpeg)
The dynamic viscosity at -40 C is only 7600 cP!
What further complicates things is that no manual transmission operates at 100C. So using a viscosity grading system that focuses on viscosity at 100 C makes little sense in this application. That's why adhering to manufacturer recommendations is not always necessary to provide good protection and good shift quality. You'll find that the kinematic viscosity at 40C varies dramatically between gear oils of the exact same grades for that reason. High quality synthetic fluids of a particular grade will have the same or similar kinematic viscosity at 100C as equivalent conventional lubricants, but they will very likely have lower viscosities at 40C and much lower Brookfield viscosities.
Lastly manual transmission fluid should be selected for the operating climate. The same car in Arizona would likely have much higher gearbox temps than one in Alaska would. If a particular fluid didn't t shift well when cold, you can always try looking for one with a lower 40 C viscosity and lower Brookfield viscosity.
