Transaxle Oil Analysis

I used a pump like this. It's easier and potentially less messy than a long funnel. They can be found at nearly every auto parts store.

 

I used a 700mm length of 8mm ID tube and the top half of a clean dry water bottle and cap. I drilled a 10.5mm hole in the bottle cap and forced the hose into it to form a funnel then used the directions above. When finished I throw away the bottle after wiping it off, I seal the hose with 2 8mm bolts to keep it clean inside ready for next use.

I purchased the oil from Toyota in a 4 litre tin, my trans took the full 4 litres with no spillage. If I put my little finger in the hole I got oil on my finger when I bent it down. I reused the washers.

 

There are no dielectric properties to the WS ATF.Please stop perpetuating this Internet myth. It is simply a low viscosity ATF fluid with good anti-shear properties. There is nothing added to this fluid to make it compatible to the "windings" because the motor windings insulation covering is extremely strong and will not fail under normal use. You would have to go at the windings pretty good with a file to hit conductive material. How many failed windings have we seen on the entire generation of Prius? Very very few. You could probably run this trans on 3 in 1 oil. Toyota Engineering is not the slightest bit concerned about this insulation failing or they would have built a special fluid...and it would be very well known as a special fluid with certain lower mileage re-fill rates. Instead the dealer touts a 100K trans refill. What does that tell you about how special this fluid is?

 

I wasn't aware of dielectric properties of the WS oil. However, I don't think I would go to the extreme of using some other oil as a cost-saving measure (penny-wise, pound-foolish). I am not a lubrication engineer, but if the WS oil could be swapped for another oil, the aftermarket companies (redline, amsoil, and, and, and) would be all over the opportunity.

 

Not in the new oil but my concern has always been what happens in service. Unlike transformer oil that is not exposed to mechanical wear, our transaxle oil does age in ways that can be detected and predicted by oil analysis and in severe cases, direct observation:

• conductive particles - these seem to increase and come from the various parts that mesh together.
• Unknown additive properties - some of the oil additives have electrical properties, especially the metal based ones. Dielectric testing would be a reasonable thing to do to virgin samples just to make sure we don't have an "uh oh" moment.

• combustion by-products - the decrease in pH suggesting acid formation in older samples suggests micro-dieseling may be going on. Since the differential gear is partially immersed in the oil pool, I suspect that is the primary source. Many combustion by-products have conductive properties. This can result in a 'paraffin' odor.

In contrast to our transaxles, transformers are bathed in oil that is not exposed to mechanical wear by-products. As a heat transfer and insulation medium, the primary design issue is the absence of contaminants. I suspect the first Prius, the NHW10, may have had a special design feature that was dropped in the NHW11 and subsequent models.

The NHW10 Prius has seals that kept the transmission oil away from the motors. This would be a conservative, engineering approach if one did not know how worn transaxle oil would behave in an environment of 300+ VAC. The later versions used an improved 'plastic filler' to seal the windings.

Internally the stator coils are cooled in part by 'sling oil' from the rotors. This means the oil is flung against the inner surfaces. Some of the photos I've seen suggest a 'polishing' but without detailed, microscopic examination, I can't say for sure.

BTW, the plastic that encapsulates the windings has chemical-mechanical properties. I would always wonder about additives or even the molecular weight of the oil that might cause the encapsulation plastic to swell and flake off. But these are speculations best addressed by testing. Still, I noticed some tiny, shiny, clear pieces after the Amsoil ATF test that suggested clear plastic flakes.

Bob Wilson

 

I didn't realize I was somehow perpetuating an "Internet myth". All materials that are insulators have dielectric properties. Seriously. Its an inherent property of the material.

Do you have a statement from Toyota that states that the dielectric properties of the WS fluid are not important? Please post it.

All that I have is the statement in the owner's manual that specifies WS ATF for the NHW20 transaxle.

Fluid type:
“Toyota Genuine ATF WS†or
equivalent


They don't specify what the equivalent is, but if Redline D6 is certified to meet the WS spec then that probably qualifies as equivalent.

Like I said before, I will be interested to see the results of your UOA. I have nothing against Redline products and I think its great that you have volunteered to be the guinea pig on this.

Personally, I don't think its worth the risk, but that's just my opinion.

I will edit my post to acknowledge your objection.

 

All I know is the only place I can find WS oil is a Toyota dealer. If there is nothing special about the oil why didn't they just specify Dextron III?

 

Your not aware of it's dielectric properties because WS has none. And of course the WS can be swapped with other better fluids. Nothing special here its a Dexron VI. Amsoil makes an excellent product & so does Redline both GL-4 full synthetics. I am running Redline D6 in my 07 right now.And its sure not cost saving as a quart of Redline is $ 10. Worth every penny in my opinion. Here's some reading for you:


http://www.redlineoil.com/pdf/3.pdf

 

OK...how is Dexron VI an electric insulator? Thats all WS is. Its just Dex VI GL-4 auto trans fluid. Any GL-4 trans fluid made will run in our trans. But for proper viscosity & shear you must at least be at DEX VI for proper gear wear. And after a few thousand miles it becomes a very poor dielectric as it accumulates metals. AT 50,000 miles of use that's a pretty metal heavy fluid.
But what am I insulating from? What are you so concerned with that I don't conduct electricity across the fluid? Your argument is that the WS fluid will somewhere in its life be exposed to voltage leaking from the MG's and given that Toy has added some space age dielectric ingredient to the WS fluid so now it can't conduct electricity so I'm OK. I'm leaking voltage from a compromised motor field wire on a MG(which is how the few that have failed did fail) a crack in the conformal coating has exposed conductive portion of the wire and 500 volts is exposed to the fluid...but I'm cool cause I got special fluids in there. The inverter is stupid. It doesn't measure voltage level...impedance...capacitance....phase...load. It just doesn't care I'm leaking voltage into the fluid. No blown fuses no crow bar of the inverter. Its just a dumb brute force power supply.I'm rolling down the road happy with sparks in the trans.
I'm busting your chops here but I'm just saying there's forces at work here that makes your special fluid in consequential.
I guarantee you if even a tiny portion of the conductive part of the MG winding is exposed you will have quite a problem even if there's space age WS fluid in the trans. The WS will not fix that problem. You have 500 volts there and maybe 100 amps of power. That kind of voltage would quickly flash over to any surrounding metal area which given how the MG is built the wiring is laying on the metal case. What type of fluid ya got in there will quickly become the least of your problems whether it has insulating properties or not.
Which is why Toyota did not put special fluid in there. Why bother. If they had made special fluid I'm sure the dealer would love to make you bring your car in every 25K miles and kill you with it. Because you have to change the special fluid. Oh and the special fluid is $20 a quart. The dealer would love it. Instead the dealer touts 100k refill. I think there's many peeps here that can tell you what 100K WS looks like. Black with metal. Not alot of dielectric properties there. And the car will still motor on down the road.For another 50,000 miles or much more. You'll have gear wear of course but your dieletric argument goes out the window with the bathwater.
I'm getting ready to take my 6K WS sample pull to the UOA place in Tampa. I'll inquire if there's a test for dielectric properties. But I never heard of it. At least not for auto products.

 

I bought WS ATF for $5.20/qt at a local dealer parts dept.

 

Hi Ed,

I can see that you have thought about this issue carefully. You rightfully pointed out that the Toyota dealers will say that the ATF WS has a 100K mile service life. Further, I have not seen any reports of 2G transaxle failures.

My motivation to perform periodic ATF WS transaxle fluid changes for my 2004 is just to get the wear metals and dirt out of the system. This motivation is probably similar to those owners who use synthetic motor oil and change it at 5K mile intervals. It doesn't hurt to follow that practice, and it may marginally help.

Its your business if you choose to use a non-Toyota fluid like the Redline synthetic ATF. However its not clear to me what benefit that fluid provides other than apparently being at a higher viscosity which results in reduced drivetrain noise (and perhaps marginally worsened mpg.)

In the unlikely event that this synthetic ATF is not compatible with the Prius transaxle and results in an unwarranted failure, then you'll face a repair bill of ~$6K. Apparently you view that risk as negligible, and believe that the benefit of the quieter drivetrain exceeds the risk.

Back in the early 90s I used Redline synthetic gear oil in the 5-speed manual transmission of my 1988 BMW 325i convertible. The problem with the transmission was that first gear was very hard to engage. By using the Redline oil, first gear became very easy to engage, and I assume that oil had a lower viscosity compared to the specified 90W gear oil.

 

Hi Patrick,
Yes sir I have given it a little thought.I believe its strictly a decision on gear wear on what quality of trans fluid you install on this particular vehicle. I like to use the highest quality GL-4 product available. And as far as warranty work Toyota would be hard pressed to tell the difference by the way Redline looks from WS fluid if any failure which I doubt will happen. They look the same. Redline maybe a little milkier. You are very correct also in that it makes a smoother ride and I do not gain any mileage. Its a smooth ride my brother. I believe its a superior product as probably Amsoil is a superior product too and the few extra $$ to extend the life of the trans is negligible. I plan on keeping this car like all my other new cars. At least 6 years or 75K. I usually sell them then and make some nice coin as a very well maintained perfectly running car. New cars ( and I have owned alot of them) for the last 20 years all you have to do is put the highest quality fluids in the car you can buy and you usually have no problems whatsoever. But the "dielectric" thing which I see constantly on this site is just silly. BTW, thanks again for the post on the evap housing stuff. I read all your posts and you really know your stuff! I appreciate it very much.

 

Just so we're all on the same page:

The range of oil additives is large and for my transaxle, I would be concerned that the additives may reduce the dielectric strength of the oil, which of course the wear materials also do. Molybdenum disulfide is one additive I would be concerned about along with any metal based additives or graphite.

Ultimately, it is your transaxle and if mineral, synthetic, vegetable or critter oil works, go for it. Just do independent testing of a 'virgin' sample so you can compare it to an 'in service' sample. Comparing results from the same lab gives a reasonable, basis for documenting the changes.

GOOD LUCK!
Bob Wilson

 

I just changed my transaxle oil for the first time at 130,000 miles. Also changed the engine oil, in at 105,000 and out at 130,000. I have samples of both if anyone is interested in having them tested. PM me if you want the samples.

 

Krous,

You ran your engine oil for 25k miles? What brand/type of oil was it?

 

ED,

What about compatibility with the insulation that Bob mentioned? Toyota would most likely have tested their fluid to ensure there are no problems with the insulation. How do you know whether Redline fluid is compatible?

 

Hi folks,

After reading this thread, I went ahead and changed the transaxle fluid on my 2nd Gen. with WS ATF from the local dealership.

I did want to mention one thing others might want to be aware of:

Presumably due to the negative pressure within the transaxle cavity, I loosed the drain plug first, and the fluid literally exploded out with a fair degree of violence, mostly onto the garage floor instead of the oil bucket directly below. Spent the next several hours cleaning up... I tried going as slow as I could, but, apparently, as soon as it was able to escape, it just sprayed and I swear, pushed the drain plug out such that it literally shot down into my oil tub.

As such, I wasn't able to get a really accurate feel for how much shavings the magnet caught, but there most certainly was maybe a millimeter or two layer of it.

 

Wow! This is a first, having the fluid jet out.

The best practice is to open the filler hole first since if it doesn't open, your car still is operable and you can take it to a shop. This also makes the subsequent oil draining more ... predictable.

I'm glad to hear no harm done and your shop floor is much cleaner.

Bob Wilson

 

Yeah, usually the negative pressure inside would cause the fluid
to bubble air *inward* as the threads started to clear. One more
reason to crack the fill plug first, and equalize through that.
.
If you had positive pressure, have a close look at your half-
shaft seals...
.
_H*

 

When the Prius has been driven for a while and the transaxle is fully warmed up, I do not believe that any significant pressure difference exists inside vs. outside the transaxle case. The partial vacuum inside the case develops after the transaxle cools down.

When the transaxle is cold and the fluid is changed, I have noticed that leaving the fill plug installed while draining causes a mess just because of the glug glug that the drained fluid makes since air has to enter the drain hole while fluid is exiting the same hole. Hence I remove the fill plug, let the pressure equalize, then the drained fluid comes out in a predictable and controllable manner.

As Bob and Hobbit indicated, it would be a first to find a situation where there was higher pressure inside the transaxle. In that case, one would expect to see fluid seeping out at the axleshaft seals.