How many ATF drain and fill?

Your Prius has simple transmission hardware (but complex software) and no torque converter. If you do a drain and refill of the Toyota Type WS fluid you will get out more than 80% of the old fluid so just do it once. Plan on doing it again in 60k miles. I have done it 4 times now on my 2004 Prius (every 60k miles - now at 279k miles) and had the fluid lab tested each time. The fluid comes out cleaner with every refresh, partly due to the small amount of old fluid left after draining, and partly due to the gears "lapping-in" as they become mated to each other with use.

I have done a double drain/refill on small motors that I am leaving sit untill the next season, so I understand your question. The $40 in extra ATF fluid to do it twice in your Prius does not seem to me to be worth the effort.

JeffD

 

It's true that a traditional automatic transmission only drains about 50%. But it's not necessary to do a triple drain-and-fill, even with those. When the drain interval is set by the manufacturer, it.s set frequently enough to take into account that you're only going to drain 50%.

The only time I would do a triple drain-and-fill is if the fluid had been contaminated.

 

Just looking at our old '86 Accord Owners Manual (misplaced when we traded up, still got it). Replacement of "transmission oil" was every 2 years or 48,000 km's (30,000 miles). So fairly frequent. It's kinda weird they don't differentiate manual vs automatic, maybe both the same.

Funny too, compared to the US Toyota Prius Warranty and Maintenance Booklet: they manage to summarize the entire maintenance schedule, in a couple of pages, in table format. The service-by-service method used in the US book is virtually impossible to "grok".