We've had this Prius for a few years now after it was given to my son. A2004 with 260K, the maintenance history was pretty bad. Now with ~280K I'm thinking about changing the transaxle fluid. I read about people who say don't bother at this point as the thickened fluid is probably keeping the high mileage unit from slipping. What think you?
He was a Master Toyota Tech at a dealership for many years. He opened his own shop about a year ago. Code: https://www.youtube.com/watch?v=jJr30r6RRgw Never Do THIS To Your Toyota and Lexus Transmission | Do's and Don'ts For Transmission Fluid The Car Care Nut 671K subscribers Apr 8, 2023
It sounds like he is talking about regular cars and not hybrids. If he is then there is nothing of relevance for the Prius transaxles. If it hasn't been changed in the last 60,000 miles, you can go ahead and do it with ATF-WS. There is nothing in the transaxle that can slip like a conventional automatic transmission, so you can ignore all that "advice"
Second gen Repair Manual doesn’t have a fluid replacement instruction (they say nothing about changing fluid in maintenance schedule). It does have a fluid check instruction (attached). there’s a link in my sig regarding third gen fluid change, mostly relevant, worth a read. If you’re on a phone turn it landscape to see signatures.
I changed mine last year at 190k. No idea when it was done before that, if ever. Didn't have any issues. Just use the Toyota fluid if you do. He wrote this in the comments: "2- This does NOT apply to hybrids. Hybrid ECVT transmissions don’t have clutches and a valve body, you can change it at any time. A good interval is between 60k-90k miles."