I have switched to Type WS and change it on an accelerated schedule to monitor wear materials. However, it looks like I can switch to a once every other year, about 30k mile, interval. The Type T-IV looks to need changing between 15-30k miles due to a loss of viscosity. There is a sticky with the transaxle oil study data. Bob Wilson
Remember the Type T-IV should only be used in the 2001-2003 Prius. From 2004-on it's strictly Type WS. Wayne
The WS oil is under $50 at Toyota dealers. I did mine at 80,000km and will do another change at 160,000km, that is 50,000 mile intervals for no reason but I think I should.
WS works on the 01-03 prius? i have used Type T-IV on one of my 01 priuses, any dangerous with going to WS? i have like 6 quarts of the WS in my garage so that would be great