Transaxle fluid... to change or not

sure, why not.

 

Probably a case of better late than never, but who knows how much longer it will go on a fresh batch.

 

agreed. it's worth a shot. at least it will remove all the crud that's built up over the last 8 years.

 

Easy peasy DIY, go for it.

 

My understanding is that you don't have to worry about changing trans fluid in the Prius at high mileage. Unlike traditional automatic transmissions, our trans does not have clutches to worry about. You should be fine.

 

ATF lubricates the gears in a "traditional" automatic transmission - not the clutch(es). The Gen 2 Prius e-CVT has gears in its single planetary gear set. The transmission fluid performs two functions - reducing friction and transporting worn metal from the gears to the magnet attached to case. There is no transmission fluid filter inside the Gen 2 Prius transaxle.

Eventually the trans fluid degrades due to thermal decomposition (it does get hot - there is no ATF oil cooler in a Gen 2 Prius) and due to debris particles that cannot be entirely drawn out by the magnet. Will this cause transaxle failure after 300K, 400K, 500K miles? I don't want to be a guinea pig. I change the ATF-WS in mine at least every 100K miles.

 

Some part of the old wives tale about not changing the ATF in high mileage transmissions is the hydraulic logic array called the valve body.

Disrupting the old fluid can cause blockages in the tiny valve body passages and the transmission works differently, almost never better. (think Stroke in the brain)

The Prius logic is electronic, it has no valve body so there are no tiny passages to clog. It is always safe to change ATF in a Prius.

 

do not use anything other than 4 quarts of genuine Toyota WS fluid.