Hey Camel, I believe that the best way to maintain Prius oil is to use synthetic at 10-13k mi intervals and analyze the used oil. If you DIY, the interval cost will be about $45.

A running record of "engine wear metals" in Prius oil would be neat because it would tell if bearings etc. were on the way out. But so far only scattered engine oil analyses have been posted to the groups. Not enough to say if synthetic oils "protect" any better than dino. So far, the only wear metals reported have been in initial oil changes.

DAS