using additive to the trans fluid

Since the transaxle has high voltage within (500 VAC on the motor generator stator windings) I recommend that you use only the correct fluid. In the case of 2G this is Toyota ATF WS. I've seen details of a few Classic transaxle failures, and those failures seem to be due to MG winding failure, not failure of a moving mechanical part.

Therefore, reducing friction does not seem to be a big issue with respect to encouraging longevity. Contaminants in the transaxle fluid may promote stator winding insulation issues; used fluid testing shows substantial Si and Fe content.

 

Patrick is right, don't use anything but the Toyota ATF WS oil in the transaxle.

 

And the Toyota ATF WS is already pretty good....

 

I couldn't disagree more. The fluid and the MG windings have nothing to do with each other. I hope this site will stop perpetuating that myth. Toyota's WS fluid is nothing more than high quality low viscosity automatic transmission fluid. Used in may different Toyota cars & trucks. Period. Nothing magical.
I have been running Redline D6 in my 07 trans for 10,000 miles and the car runs fantastic. Marked difference compared to the WS fluid. The car's trans runs smoother, cooler and quieter.
Your on the right track. There is a better product out there than WS fluid.
Any discussion based on the WS fluid should be strictly about its GL-4 lubricating properties.
And as far as winding failures I think out of the since 1999 thousands produced Gen 1's there's maybe 2 with documented winding burn out with pictures. I don't think any Gen 2 failures of winding have been reported. No mention of conformal coating failure.Motor windings fail from excessive current draw rarely from conformal coating failure. Easiest way to kill an electric motor is to low volt it under load. Try leaning into an electric drill on a 100 foot underrated extension cord. It will smoke.
We have 2 recent postings of inverter failures that the dealer later reported mg failure also. I suspect inverter failure where the owner's continue to drive. The failing inverter's low volt the mg's burning up the mg windings. I contend this is alot more plausible than fluid failure which if the case Toyota would surely issue a TSB requiring at the owners expense of course a more rigid cvt fluid maintenance program than what is presently the norm which is every 100K.

 

Ed, are not the MG windings constantly exposed to the fluid?

 

See Florian Steiper's photos of his disassembled NHW11 transaxle, especially the photo of the stator windings. As Richard pointed out, the stator windings are in contact with the transaxle fluid, and debris from the burnt windings ended up in the bottom of the transaxle drain pan. See for example:
MG2 Stator windings on Flickr - Photo Sharing!
Oil Pan, close up of the pickup magnet on Flickr - Photo Sharing!

 

What is your source of this information?

 

Seems to me that edthefox5 has adopted a somewhat contratian view and offered his own vehicle as a test case. Fine by me. I just hope that he makes it a more complete/compelling study by performing ocassional fluid analyses. If tragedy does strike, then there will be even more reason for him to get the fluid tested.

If in fact a myth is being perpetrated here, the best way to counter it is with data (fluid test results). For the moment, the most likely source of that data would be Ed's transaxle.

 

I'd also wonder in what way it's "smoother" with non-standard fluid, since it never shifts.

 

Of course they are. The point in question is what specific relationship does TOYOTA WS FLUID have to do with the windings. Everyone seems to think disaster will strike if any other fluid is used besides WS fluid. Thats bullsh*t and I have used my own brand new vehicle to prove it. WS fluid is not car specific to the Prius only. Its used in many other Toy vehicles like the Tundra. No windings there. What is this magical special ingredient contained in WS fluid that nurtures conformal coated windings? PCB's? Transformer oil? Mineral oil? My contention is there is none.
Why should there be?
Our trans is a sophisticated gearbox that happens to have motor windings
in its gearbox. Toyota engineers went to great lengths to make the coatings on these windings quite hardy. Exposing them to 100 degree transmission oil is not a problem. No special fluid needed. I can prove it. How many gear boxes have failed in Gen 1 cars with specific "winding failure" since this car was rolled out in 1997?
I have only found 3. There's a caveat here though. Why did those windings fail? Did horrors of horror someone use the wrong fluid? Or was the MG's so abused the stators failed drawing big current through the windings? Or my contention....low inverter B+ low volting the MG under load. Certain death.

 

I'm sorry, when you said "have nothing to do with each other", I took that to mean "are never in direct contact with each other."

I see now that what you meant was that you believe that they are in contact with each other, but that the windings are designed such that any standard transmission fluid used in any other vehicle can be used without risk of damage to the windings.

While I have no specific reason to doubt this assertion, I can't help but wonder if there is any significant difference between transmission fluids with regards to things such as:

Ability to transport heat
Electrical Conductance/Resistance
Viscosity

 

Danny,
I have no source for my contention but can you show me any info to the contrary? No one can tell me why every time there's a trans fluid discussion on this site there is the inevitable oh you better be careful there's 500 volts in there you must only use this fluid. Please tell me why? But the WS fluid is not that critical so change it every 100K. What? How can it be that critical if its a 100K only maintenance? Then we see poster after poster here complaining of the condition of 100K plus fluid. How burnt up it is, and there still rolling down the road. It don't make much sense the hi voltage/ws fluid argument.
I've searched and searched and there's nothing special about the WS fluid. It was designed in 2001 as Toyota need a new high quality LOW viscosity trans fluid. Its good quality fluid no doubt but there's better out there.
Redline makes the best GL-4 lubricant on the market. Thats pretty well known in tuner circles.
I would like to keep this car at least 5 years and like running the best fluids on the market. 10,000 miles later Redline fits that bill and is listed on there website as a direct replacement fluid for this car.
I did a temperature study on the trans & inverter. The trans is running cooler after Redline. Its quieter. And yes its smoother. I made a run to Orlando last weekend and ran about 85 all the way there and back and averaged 48.5. The car is awesome.
I'm running Redline 5-20 oil in the motor and Redline Water Wetter in the Inverter and radiator. I highly recommend Water Wetter in the Inverter coolant for its anti foaming and anti aluminum corrosion properties. Really good stuff.
In fact I can't wait till the Integrity tires go because when I'm cruising at 80-90 all I hear is tires. its really a different car. I'd love for someone else to try this product and tell me I'm full of it but they will be very pleasantly surprised.
There's a better way.

PS: I love this site. I have learned everything I know about this car from this site especially from guys like Jayman & Patrick. Props to you guys. Thanks alot Danny.

 

I agree with Doug that experimentation is how we learn. I'd just like to share a few comments:

The "potting" compound is in contact with the oil that slings against the outside of the stator coils and takes away heat. So chemically it needs to be neutral to the potting compound at relatively high temperatures, 85-95C (measured temperatures from my NHW11 on summer days at 65 mph cruise speeds.)

Actually the Type WS viscosity range is closer to the transmission oil used in turbines.

The Type T-IV is used in other mechanical transmissions. However, my testing with Amsoil ATF, a viscosity range equivalent, revealed a disturbing increase in copper. I don't recommend Amsoil ATF in an NHW11 transaxle and the viscosity range is not appropriate for a Type WS substitute. The materials in a transaxle can react to the additives in a transaxle oil so oil testing is important.

How did you measure vibration and temperature? Any quantitative values?

Actually a discussion is based upon sharing our best understanding of the salient properties. Hopefully these are backed up by empirical data of the product in service not just repeating the manufacturer's lab specifications. Of course, folks are free to choose how they wish to approach an experiment.

I have photos of three: (1) Washington State; (2) Florian's; and (3) Art's Automotive. Over in Prius Technical stuff, we have credible reports of two from Sacramento and one from Kansas City. We've had some other reports but often the owner reads our postings and we never get any follow-up.

I remember one California NHW20 failure repaired under warranty.

My Amsoil pan debris was analyzed and there were tiny, clear plastic particles seen in the debris. Unlike the NHW20, the NHW11 has a pan that makes collecting and debris analysis somewhat easier. However, there is one area under the differential that I would love to reach without having to disassemble the transaxle.

There are other failure modes such as shorting and arcing. That one failure mode can be replicated with common, household items does not tell us if the transaxle stator failures we've seen had the same failure mechanism.

An interesting hypothesis. How would you propose to test it?

Transaxle failure mechanism(s) are still under investigation. Over in Prius technical stuff we are also looking at a new hypothsis, partial discharge. However, I'm not ready to ignore transaxle oil test results showing: (1) greater than 15% viscosity loss; (2) significant particulates in the oil; and (3) higher levels of metals in the oil. As an owner, I have a vested interest in all data.

It makes sense to start with the designer and manufacture's recommended schedule. But once bought, the owner is free to modify their maintenance schedule as local conditions, desire and they have time and interest.

In my case, I prefer experimental data that includes cold temperature hill rolling tests, instrumenting the oil transaxle temperature as well as oil sample testing. It is also backed by reading relevant technical papers and lubrication journals but this is just one owner's approach.

Bob Wilson

 

What I've seen:

• Ability to transport heat - I haven't seen any figures on specific heat, the ability to pickup heat and transport it.
• Electrical Conductance/Resistance - my oil testing service also handles transformer oil testing. However, I've not submitted any samples for this testing but have been thinking about a home-brew system. I'm interested in an electrostatic filter system.
• Viscosity - here we have an abundance of data for Type T-IV, Type WS and Amsoil ATF in the files section of the Prius SAT2 group.

One important element missing is the chemical reactivity to: (1) stator potting material; (2) other transaxle materials including sealing material and metals; and (3) reactive wear material.

We are also seeing evidence of micro-dieseling from the differential. This is probably the primary source of increasing acidity seen in some of the samples and the darkening may be from combustion by-products. It is an area that begs investigation.

Bob Wilson

 

My view is that Toyota did extensive testing of HSD in a multitude of HSD transmissions and decided to use WS oil, if you know anyone who has done more extensive testing than Toyota with success then by all means follow their recommendations. I have a feeling they did a little more than 10,000 miles of testing.

Remember the old "keep the feeling" ads for genuine Toyota parts, I used to laugh at those ads till I discovered they are right, genuine Toyota parts are generally better.

 

The point is that Toyota has established that the WS fluid does not degrade the winding insulation even over years of contact at high temperature. Experiments with other fluids and additives just to see what happens strike me as pointless and rash. If your transmission blows up some day you will let us know, right?

 

Another issue to consider is that no other ATF appears to have the low viscosity that WS has. Virgin oil analysis of WS seems to show a 100C cSt of about 5.4 and in use rather quickly shearing down to 4.7 or less.

Amsoil ATF has an initial 100C cSt of 6.8 which is not a great match. Redline D6 has an initial 100C cSt of 6.4 and is stated to never drop below 5.4 which is a better match than the Amoil but still seems a bit thick compared to the WS.

If Redline or Amsoil (or Mobil or Schaeffer's) would come out with a better viscosity match for WS in a full synthetic, I would be willing to try it. But as it is WS's light viscosity seems to rule out these other fluids. The main point of a Prius is it's fuel economy and I'm not willing to take a hit because of thicker ATF, even if it might be a small hit.

Rumple

 

I am not doing an experiment just to see what happens. I believe Redline fluid is a substantial improvement over the WS fluid. And your statement concerning my trans blowing up only furthers the misinformation concerning this situation.

 

Hi Bob,
I was wondering when you were going to weigh in. And I apologize not including you as one of the people who I have learned so much about our cars from. You have done some excellent work here. Let me respond please:


The "potting" compound is in contact with the oil that slings against the outside of the stator coils and takes away heat. So chemically it needs to be neutral to the potting compound at relatively high temperatures, 85-95C (measured temperatures from my NHW11 on summer days at 65 mph cruise speeds.)

In "potting" I assume you mean the very hard conformal coating on the windings. Not having done an oa on this product yet not sure about its acidity. I plan on taking a sample this weekend. But I feel the windings coating is extremely tough and could only be compromised by very very high operating temp from extreme super duty use not from chemical attack. Or my suspicion low volting the MG. That can superheat the windings in an
instant.


The Type T-IV is used in other mechanical transmissions. However, my testing with Amsoil ATF, a viscosity range equivalent, revealed a disturbing increase in copper. I don't recommend Amsoil ATF in an NHW11 transaxle and the viscosity range is not appropriate for a Type WS substitute. The materials in a transaxle can react to the additives in a transaxle oil so oil testing is important.

Yes Type T-IV is used in other vehicles. Can I assume that the winding friendly compound you all are so sure is contained in the WS Fluid is also in the Type T-IV? We have the same windings in Gen 1 cars. How come if this compound is so important you installed Amsoil fluid in your car? Amsoil does not contain this compound. I looked back at the posts and I see no one posting that your going to blow your trans up running Amsoil and you were not concerned either until you pull and OA and found high copper content. Remember the link I sent you stating Amsoil attacks copper? The Gen 1 bearing races are exposed. Gen 2 has sealed bearings.

How did you measure vibration and temperature? Any quantitative values?

Yes I measured the trans temp before and after the installation of the Redline fluid. And the car feels smoother to me. It accelerates smoother and seemingly with less effort.There is an obvious improvement.Try it and see.It won't ruin your trans. I'm going on 11,000 miles with mine and the car actually runs better than when I bought it.
I tried Redline's 5-20 motor oil as going for 10K replacements. Always ran Mobil 1 5-30 since 1K. Going on 2000 miles with that. I am noticing now when the ICE powers on & off it does it now with no shaking or drama. I do not even notice it now and it has not done the clunking shutoff since I installed this new oil.
Jeez...this should start a whole new bunch of your full of sh*t posts.


I have photos of three: (1) Washington State; (2) Florian's; and (3) Art's Automotive. Over in Prius Technical stuff, we have credible reports of two from Sacramento and one from Kansas City. We've had some other reports but often the owner reads our postings and we never get any follow-up.

Bob thats a tiny tiny fraction of the vehicles made. Thats an incredible testament to Toyota quality.I think they have thought this winding coating thing through.



I remember one California NHW20 failure repaired under warranty.



My Amsoil pan debris was analyzed and there were tiny, clear plastic particles seen in the debris. Unlike the NHW20, the NHW11 has a pan that makes collecting and debris analysis somewhat easier. However, there is one area under the differential that I would love to reach without having to disassemble the transaxle.

Could that have been assy debris possibly flushed out with the Amsoil charge? I doubt its the failure of the winding coatings because any raw winding exposure no matter how small to fluid would be catastrophic to the Inverter & trans. Even a pinhole would arc at the voltage and current the MG's run at. Your still driving down the road supports this.

There are other failure modes such as shorting and arcing. That one failure mode can be replicated with common, household items does not tell us if the transaxle stator failures we've seen had the same failure mechanism.

An interesting hypothesis. How would you propose to test it?

I can't.

Transaxle failure mechanism(s) are still under investigation. Over in Prius technical stuff we are also looking at a new hypothsis, partial discharge. However, I'm not ready to ignore transaxle oil test results showing: (1) greater than 15% viscosity loss; (2) significant particulates in the oil; and (3) higher levels of metals in the oil. As an owner, I have a vested interest in all data.

I think you may be able to ignore alot of that concerning its impact on winding failure though. With the dealer network trained to tell customers replace your trans fluid at 100k miles. Thats insane. Can you imagine how poor 100K fluid must test? How metal heavy it must be? 100k miles at an average of 15k a year thats almost 7 years before you replace the fluid.
Obviously the factory is not the least bit concerned about the fluid.
But why should they be? Its an excellent trans with an extremely low industry failure rate. It consists of a very precision planetary gear set. No pumps no valves no switches no turbo's no fluid under extreme pressure no cooler etc. Just a big sewing machine that happens to have motor windings in its gearbox. All it needs is some excellent gear oil.

Always a pleasure Bob.