Hi folks,

This note is about an on-going transaxle oil analysis that a bunch of us over in "Prius Technical Stuff" have been conducting for the past two and a half years. It started when I replaced my NHW11, 2003 Prius transaxle oil with Amsoil ATF (DO NOT USE Amsoil ATF in transaxles!) So this is the latest posting:

> I just uploaded six samples that I'd been meaning to send out for a
> while and got around to it this week. The samples results are in one
file:
>
> 309512 - Jessie's sample at ~325k miles, NHW11, Type T-IV
> 309513 - Virgin, Type WS in a low, wide jelly jar with bottom coated
> with sealant, 8 months exposure on shelf behind passenger seat head
rests.
> 309511 - UT NHW11 using Type WS, 27K (Looks good!)
> 309509 - CA NHW11 after 2K miles, new transaxle, user wanted Type T-IV
> 309508 - AL NHW11 after 8k miles, flush out residual Amsoil, drain
> plug sample
> 309510 - AL NHW11 (same as above) filler plug sample
>
> First impressions:
> 1) Transaxle sealant is a significant source of Si. Trace of Sn.
> 2) Type WS looks good in UT transaxle.
> 3) Holy Cr*p! Where did Jessie's Ca come from???
> 4) Filler plug seems to have a little more Cu than drain plug sample
> but drain has more Ca ... a puzzle.
>
> I'll be doing some more analysis later but I suspect that after the
> initial Si leaching, the rate drops down. I'm still not ready to throw
> out the dirt/contamination hypothesis but factoring the sealant makes
> this more difficult.
>
> Enjoy the data, I'll try to add it to my spreadsheets to see if
> something else jumps out.

I loaded the latest six samples into a spreadsheet and with these samples, found some things I'd not noticed before:

1. Nickel and aluminum appear to be a good indicators of service mileage wear.
2. Iron has an initial spike and then becomes a secondary wear indicator.
3. Do not take my two 8K samples as indicative of normal Type WS usage since I had ~15% carry forward from the Amsoil ATF test. But the Cu, Ca and P appear to be the signature of Amsoil, which has one report of being hostile to 'yellow metal', bushings. Seriously, don't use Amsoil ATF in our NHW11 transaxles and it is not a Type WS equivalent for NHW20 transaxles!
4. Zinc appears to be a potentially good indicator of transaxle oil wear. It seems to go down as the oil remains in service.
5. What is with Ca from the high mileage, Jesse's sample!?!? This remains a puzzle and I have no explanation.
6. I suspect the initial Fe and Si loads are coming from the initial service.

I need to integrate these data with the master spreadsheet to see if these patterns hold true (don't wait on me, feel free to run with the data.) These six samples suggest:

• Early transaxle oil change with first engine oil change - this change removes the Si leached from the sealant and Fe from the initial 'polishing' of the gears.
  
• (OPTIONAL) second engine and transaxle oil change - this will get the 15% carry forward that remains in the transaxle after draining and now diluted in the oil.
  
• Zinc depletion may be a useful oil wear indicator - Blackstone does not do 40/100C viscosity testing and the 40/100C viscosity test costs extra from R&G Labs (formerly PdMA.) However, we need more, diverse, virgin samples to make sure zinc starting levels are held constant.
  
• Calcium remains a mystery - I have no idea what it means or where the heck it came from.
  
• Type WS for Type T-IV looks OK - the wear down (probably shear down) viscosity loss of Type T-IV appears to rapidly approach and level off at the initial viscosity of Type WS and hold constant. IF shear down is what is going on, it means softer metals (aka., bronze bushings) would be especially at risk until the oil 'thins.' IMHO, this is a bad thing for our NHW11 transaxles, which have at least one bushing.
  
• Tin appears to be a sealant trace - it may be possible to use Tn to isolate Si from the sealant from environmental sources like dirt or grit.

Bob Wilson

ps. Standard units:
miles 2k -> 3.2 km
miles 8k -> 12.9 km
miles 27k -> 43.4 km
miles 325k -> 523 km