I was hoping Bob might comment on his thoughts. Is it worth on a Gen 1 if you are doing your transmission fluid change yourself to stick with Toyota ATF T-IV or use the WS. Since warranties don't matter anymore I was wondering what is best on lower milage older Gen 1s. All we have to go by is some older posts like this: Transmission/Transaxle Fluid Replacement ? | PriusChat
The only field differences I've found occur at freezing or below. This was from my testing of the original 56k service mile Type WS vs. AMSOIL ATF. Hill roll-down tests in cold weather showed clean, new oil was much better. Later, oil testing revealed the AMSOIL problem with 'yellow metal.' Since then, I've had a chance to look at over two dozen oil samples and noticed: Type T-IV shears down to Type WS new viscosity Type WS viscosity shears down at a lower rate than Type WS (aka., keeps viscosity ratios closer to new) I personally continue to use Type WS in my NHW11. The most recent oil testing shows slightly higher copper wear but nothing like AMSOIL. The viscosity numbers look good and other NHW11 oil test results with original, Type T-IV continue to show it 'wears down' to Type WS viscosity in 30k miles. The oil testing data suggests our NHW11 transaxle oil should be changed about 30k miles regardless of oil type. Similar testing data of NHW20 samples show it is OK with a 60k change interval. One NHW20 owner has data suggesting he can go to 90k miles after three, 60k are done. BTW, the Prius c SAE paper on the new transaxle discusses the all-ATF cooling that eliminated the inverter coolant channel. That paper sees warming of the ATF fluid as an efficiency improvement by early reduction in viscosity. Bob Wilson
Thanks for you expertise. I know you mention the parts dept always has to order the gaskets, but do you think it is possible there will be a shortage of gaskets one day because they only exist for the NHW11 and there were so few sold? Also, have you put in a hard drive magnet in the bottom of the pan? The only downside I could see if that it is so strong it could make a larger gunkball as it can keep attracting more stuff when the weak magnet just quits attracting after it is surrounded. Of course I supposed if you change every 30k you won't need to worry.
Was there any more discussion on this: I think WS makes sense, the only consideration might be something to do with bearing metal. (maybe cost). I'm not sure what determines the transmission wear other than temperature of the motors and possible really bad fluid (maybe driving behavior?)
There are 'generic' gasket material available on Ebay and other sources. I don't see it as a problem. I'm still using the OEM magnet. The oil velocity in the pan is to low I suspect a refrigerator magnet would be just as effective ... but I haven't run the test. Bob Wilson
I've seen posting of about a half-dozen, MG2 burn-out transmissions but never one about a bearing failure. If we'd seen even one posting of a bearing failure in an NHW11, I would give more weight to the heavier Type T-IV. But we know 'heat is the enemy.' Bob Wilson
I know that edthefox used another fluid (amsoil?) in his NHW20 and actually took a lot of heat at this forum about that. AFAIK he did not post any test results on that fluid after it came out? He may have done so and I missed it. The most conservative would probably stay with T-IV. I and several others switched to WS in the NHW11.
