ATF fluid changes ARE Required.

I suppose they could measure amounts of dissolved varnish or epoxy, but only if that's something they measure. And I don't know what levels would mean what.

 

At least the color of transmission fluid that has worked for one hundred and fifty thousand miles is completely different from fresh fluid. Old transmission fluid looks like dark cherry juice, new one is more of a raspberry shade. The consistency is equally liquid at first glance, but here it is better to have a laboratory analysis. And of course the content of metallic impurities that can form when gears interact.

 

I believe I've seen something about it in Toyota docs (from the tech side of the house, not something a dealer service writer to some gullible customer).

Not having that reference ready to hand at the moment, I won't use this post to argue with you about it. Here's hoping you'll be equally open to new information if I or someone else lays hands on it.

 

It seems to me I’m heeding the need to use one specific Toyota product, Toyota ATF WS, because the owners manual says, just for this one application, that anything else could cause damage, expensive damage.

the argument that they’re advocating this to get rich rings hollow, when they don’t recommend a change interval.

I suppose it’s a free-speech world now, but why not stick to second guessing Toyota’s warning just on your own car?

Are you a chemist, electrical or mechanical engineer? I sure as heck am not, so choose to respect their caution.

 

Spare me...

 

The history with that in gen 1 Prii was already mentioned upthread.

 

That seems a slight deflection from the fact that your question was "Has there ever been a failure blamed on 'insulation break-down"?, that is, whether there has or hasn't been real-world reason to think about one of the topics of this thread.

It does seem that Toyota was able to reduce the incidence of insulation break-down between gen 1 and gen 2, through something, or some combination of things, that they changed between those two generations.

 

I have a master's in mechanical engineering, so I use Valvoline

 

We do not know if Toyota changed the insulation to fix the problem or that the change to WS ATF fixed the problem. All we know is that using WS ATF is safe according to Toyota and the history of no (?) winding failures in Gen2+. Other ATFs may be safe, but I will not choose to do the required testing on my Prius.

JeffD