Transmission fluid

Yeah to read it, it was most expedient to post first.

for ref, 3rd gen attached:

 

It is true that procedure is unnecessarily confusing. My understanding is that 2(k) is the second time Toyota wants you to drain, refill , start the engine. And 2(l) is the last time (the third) when Toyota wants you to just drain, refill and tighten the fill and drain plugs without starting the engine. As far as I can see for Gen5 there is only replacement procedure there is no longer adjustment (simple drain/refill) procedure since now it is considered to be a non-maintenance item and therefore unwillingness by the dealer to do simple drain/refill as Hammersmith suggested. So is it general consensus that a single drain/refill is completely adequate if there is nothing wrong with the older fluid and there is no need for a complete purge of the transaxle?

 

By the way, I called Valvoline and Amsoil and they said they do not have a product for Toyota TE e-transaxle fluid yet.

 

I’d say so, with the caveat to measure volume of drained fluid, compare to spec capacity (amount needed to fill brand-new, dry transaxle). It should be around 90%.

FWIW, even with their conventional automatics, where drain- and-fill replaced only about 50%, Honda still just called for a single drain/fill.

regarding unnecessary, awkward complexity, Toyota’s 3rd gen brake fluid replacement instruction is a similar doozie. To explain the order the four brakes should be done, they more-or-less repeat the entire procedure, four times (once per corner), with sole change being the ID of which corner it is. And of course instead of saying right hand (for example) they say RH. A plan view pic of car with the numbers 1 through 4 would save about 500 tedious words.

 

But Toyota dealerships do have it? I’d be reluctant to use anything else, even if there were options. Does the owner’s manual still warn that alternative fluid may cause damage?

 

The warning is still there for Gen5 but I do not believe that TE fluid is anything special. Because if you look at WS fluid - it was used in regular stepped automatic transmissions and magically it was good for hybrid transmissions when they came out. I am pretty confident Gen5 will take WS fluid and will be even better protected since WS is slightly thicker. If WS is good for Rav4 Prime it has to be good for Prius prime as well. All transmission have the same gears, the same friction materials, the same solenoids, same pumps. Even AISIN that makes supposedly "unique" fluids makes universal fluid which can be used in place of fluids which according to AISIN itself are incompatible! If you have not seen it already read the section "What about universal/multi fluids?"
What ATF/CVTF to use for Toyota?
I think the problem is licensing. I was taught in the university that the licensing is a form of a barrier manufacturers set up to prevent other companies from entering the market place. It makes it too expensive for many companies to acquire all the licenses.

 

Hardly "magically" - those hybrid transmissions were designed to use it.

There's no evidence the transmissions calling for TE were ever designed for WS, is there? It's not like they've just changed the manual for a transmission that previously called for WS.

I mean, it's possible that they were originally designed for WS, and were tested with TE later in development, but I don't think there's anything to suggest that - so it could just as well be the case that they're relying on the lower viscosity and it will perform really badly with WS.

Based on what logic? The common word "Prime"?

Well, they all have gears, materials, solenoids, and pumps, sure, but obviously not the same. The moving parts are designed with particular tolerances and gaps.

With e-Transaxle TE not among their list.

 

In the Gen4, the transaxle now has an external cooler in the car's radiator. Any particles in the fluid will mostly settle out in the many passages of the heat exchanger before the fluid all drains out. It may not even completely drain of fluid. The multiple drain and fills is likely to flush out the exchanger in the event of contaminants.

This may still be the case with the gen5, or it is simply a copy and paste from the gen4 manual.

Earlier hybrids used WS because Toyota was making barrels upon barrels of it for their automatics, and the number of hybrids being didn't warrant making a power-split hybrid specific fluid.

There is no physical shifting going on in these transaxles; no stepped gears, nor belt and cone, nor a torque converter. So no need for the fluid to also work as a hydraulic fluid, or wear from clutches. Additives needed for that aren't needed for the transaxle. Taking them out means more space for actual lubricant in a given volume of fluid. It also means the fluid can be designed to be more heat tolerant.

 

Yeah, this is a really bad take.

TE fluid is speced for the 5th gen transaxles. Those are currently the PA10, PB10(Prius), PB11, & PB12(Prius Prime). The current RAV4 Prime uses the 4th gen P810. We'll see what the 2026 RAV4 uses when it's updated to the 5th gen system later this year, but I bet it's going to be TE like the rest of the family.

 

I'm just smart enough, to not second guess them on this. From my perspective, there's zero upside and a lot of potential grief, considering how adamant they are about using only the proprietary fluid.