Transmission Fluid

Which AWD? Prius AWD doesn’t have a conventional rear differential with fluid, as far as I know.<never mind…

I’m sceptical they would screw up on a spec like this.

 

That doesn't sound right to me, either....why would Toyota move away from the tried-and-true WS?? Even my rear differential in my 2021 AWD Prius just takes WS.
New models are sometimes slow for specific maintenance data to come out since they aren't needed right away.
Thankfully, you don't have to worry about it until you hit 5-years or 100,000 miles!

 

My rear AWD differential (2021) takes about 1.3 qts of WS....it's supposed to be changed every 25,000 miles so will be doing this service in a week or two when she hits 5,000 miles since her last oil change.

 

Seems to be correct.
Development of Transaxle Fluid for Electrification Vehicles
"The fuel economy in the Toyota Hybrid System (THS) was improved by 1.0% and more compared with the ATF because of the significant viscosity decrease in the developed fluid. This fluid will be widely used for HEVs, PHEVs, BEVs, and fuel cell electric vehicles (FCEVs) and can contribute to the realization of a carbon-neutral society."
Development of Transaxle Fluid for Electrification Vehicles: Design of Novel Additive Formulation

ATF has two main jobs; lubricate and act as a hydraulic fluid. The THS transaxle has no use for the hydraulic duties, but the ATF Toyota had on hand was lower viscosity than their fluid for manual transmissions. So that is what the Prius got. Over 20 years to develop something specific for their hybrids seems a bit long though.

The abstract doesn't cover it, but does this new fluid have a higher heat tolerance than the ATF?

 

The Crown is using the engine and hybrid system found in the Camry and Highlander and other models, which came out before the paper was published. Toyota will likely stick with the ATF in it.

Or you have a Platinum trim, which is a parallel hybrid with a true six speed transmission.

 

It is correct. It has reduced viscosity for higher fuel efficiency (E suffix), intended for MG-controlled transmissions as in Prius.

https://toyota-club.net/files/faq/03-03-29_e77-04_eng.htm

 

That is the e-transaxle fluid TE.

However, there is some hogwash in that Toyota paper, as there is no such thing as an oil-film-forming polymer. They are talking about the viscosity-modifier (VM)—also known as the viscosity-index improver (VII)—polymer, which does not contribute to the oil film in high-shear environments like a gearbox. Therefore, hopefully the increased antiwear-additive content will make up for the reduced oil-film thickness due to the reduced oil viscosity and we will not see increased transmission wear.

 

They are either being translated from Japanese by someone, or that is their own translation into English? They are likely Japanese first language thinking engineers, is my guess.
For me it is as simple as using what Toyota says to use, no second guessing them. So far, they haven’t failed me with wrong parts. Their testing is good. On my Prime, all I need to do is drive it and go by the manual. I tend to do more often oil changes, but not less. You can look at your own mpg and mpge and wonder “how did they do that?” I do anyway and it’s sort of a hallmark of Toyota, get more than expected. Not always, but often enough.

 

No, it is not a translation or foreign-language issue. It is a lack-of-knowledge issue. Few engineers know how the VIIs work as a function of the shear rate, and these certainly did not. A VII polymer would hardly contribute to the minimum oil-film thickness in a gearbox because of the very high shear rate. They certainly do contribute to the minimum oil-film thickness in journal bearings, but the shear rate there is much lower due to the different geometry.

Nevertheless, I agree with you that there is no reason to doubt that the new ATF will offer sufficient protection against transmission wear despite being much thinner.