I'm attaching my NHW11 oil test of Type WS after 27k miles. My overall impressions: viscosity 5% loss - very nice! Cu 73 ppm - higher than desired but post Amsoil Si 33 ppm - excellent, little sealant leaching B 62 ppm - excellent, additive remains The Cu rate is higher than desired but I suspect the bushings may have been damaged during the Amsoil tests or even the original oil that tested horrible. All in all, I'm OK with these results but I might be able to do better. One possibility is mix of Type T-IV and Type WS to create an intermediate viscosity oil. The theory is a worn bushing may be somewhat more protected from wear by a thicker oil. However, it isn't clear if this is wishful thinking or something that has any supporting test results. Bob Wilson
Hi Bob, Thanks for sharing these used oil test results. Have you found that WS provides a measurable mpg improvement compared to T-IV? If that improvement is not significant, compared to the risk of bearing deterioration, why not go back to ATF T-IV?
Tochatihu got 1-3 mpg better with WS in the transaxle compared to T-IV. A wide range of uncertainty because I was not holding other factors constant. Bad scientist.
Like Doug, I can't separate the other variables. What I do know is replacement of the worn out Type T-IV with clean Amsoil ATF improved the hill roll-down test. Both have similar low temperature viscosity. The data suggests my NHW11 bearing problem started with the Amsoil. Look at the rates: Column 1 Column 2 0 Cu ppm/1k mi sample 1 1.41 53k original Type T-IV 2 4.0 7k Amsoil 3 4.9 27k Amsoil 4 4.9 8k Type WS in NHW11 after Amsoil 5 2.7 27k Type WS in NHW11 6 ... ... 7 3.0 2k Type WS in NHW11 CA 8 2.0 325k Type T-IV Jesse 9 1.8 27k Type WS in NHW11 UT 10 1.5 44k Type T-IV . I'm still not ready to go back to Type T-IV because of the high starting viscosity. At this point a higher viscosity would likely put more stress on the bushings and remove the boron nitride on the surface. But I've been late in sending four other samples and they may provide more insights. Bob Wilson
Shubin, we don't want to save $20 on fuel at the risk of spending $2000 replacing the box of gears. That would indeed be crazy. I hope that you are at least considering changing the transaxle fluid in your NHW11. What you replace it with is up to you...
thank you about worry my prius maitanance. there was something more than simple changing the transaxle fluid discussion. so i wrote that i wrote
Patrick Wong has every right to express concerns about non-standard transaxle fluids in the NHW11 (or any other car). So far only a few of us have tried Toyota WS, Amsoil or Redline. Used oil analyses on these test cases are the only way to find out if some are bad choices, and the number of tests is still too few to draw conclusions. But the focus for now seems to be on copper. An mpg improvement is intriguing but I don't really think it is the motivation for most of these experiments. Type WS or the others might be better in some other ways in the NHW11 transaxle. Energy dissipation by fluid churning in there (on the chain, etc.) is not just robbing some fuel economy, it is putting heat where we don't want it. Only those who are interested in experimenting on their Prius should probably be doing such things. But I'd like to see periodic transaxle fluid replacements done throughout the Prius fleet.
