I was buying today the WS ATF oil from local dealers and at least two parts guys mentioned that there is no need to have the tranny oil changed under 100K miles. I figure it won't hurt but did some research anyway. Read the excerpts below from http://www.bobistheoilguy.com/forums/ubbthreads.php/ubb/showflat/Number/783659/site_id/1#import: "We just tore apart a Prius transmission with almost 200k miles on it from one of our cars, wrecked. It as no torque converter, no clutches, just a few gears. It looked like new inside. It has a sun gear, a ring gear, and a few planet gears and that's it. There has been a lot of talk about the Prius and we all wondered how reliable it would be. We pulled the pan off the engine and look at the bearings and they are like new. We looked inside the cylinders and everything there looks like new too. The batteries are also as good as new. We did that load test on them and it's impressive how much power there is, there. But back to the transmission. I can't imagine how you could wear this thing out. It's made like a swiss watch and the gear wear patterns are almost not there. It also looks like this thinner WS transmsission fluid is doing its job, too. With only one forward gear and no reverse this transmission is the ticket to a along life. "
The mechanical gears are not the risk. It is the windings of the two motor generators that are at risk. To see this failure mode: http://www.ipernity.com/doc/florians/album/32724 We continue to track transaxle failures and so far, the clustering appears to be in the 2001/2002 year but there are not enough samples to tell: Thanks to Florian's photos, we believe stator winding failure results in: excessive transaxle heat - the shorted winding provide nothing but heat as the short robs mechanical energy to generate the runaway currents that continues to burn the windings 'howling' or 'vibration' or 'rubbling' - the magnetic coupling causes impressive stresses on the rotors that can be felt by the driver We have not found a 'first cause' of the stator failures. Potential failure modes are: latent manufacturing defect or oil contamination triggered spark or short. Along the way, we've started using oil testing to get an idea of what is going on as well as some UT Battelle reports on transaxle dynamics. I'm not surprised that the mechanical parts show almost no evidence of wear. It is the stator windings that are at most at risk and that is very difficult to detect before a short turns a stator into a mixed mass of burnt windings. Bob Wilson
