Hi folks,

I have started testing Type WS transaxle oil in my NHW11 03 Prius transaxle. The OEM oil is Type T-IV and I recently completed an Amsoil ATF test (NOT recommended due to excessive copper in the oil test.) I've installed a new transaxle pan with a JC Whitney heater and a drain plug with a small hole for drawing intermediate samples:


The first Type WS, 1.5k mi report, 278712, arrived. I had expected some cross contamination from the inaccessible areas but I was surprised by the amounts. Based upon viscosity, there was at least an 18% dilution. The wear and contamination materials (aka., inaccessible sludge and additives,) suggest it is closer to 25%:


This first test data suggests a transaxle flush is needed for our Prius. Since the NHW20 does not have a pan to drop, I will work on a system that uses the three major plugs: drain, side-fill, and top plug. It will recirculate the flush fluid to minimize wash fluid loss. Furthermore, it will use an NHW11 oil pickup screen and pipe with an in-pan, oil filter, to let us know when the flush has taken out all that can be easily removed.

I think the external, transaxle oil filter modification makes sense and this is the only alternative for the NHW20s. However, I think an in-pan filter that fits around the oil pickup screen may be a simpler and quite adequate solution for our NHW11s, 2001-03 Prius.

Bob Wilson