Transaxle Oil Analysis

[Patrick Wong]

Originally Posted by edthefox5

...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...

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.

[edthefox5]

Originally Posted by Patrick Wong

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.

[bwilson4web]

Just so we're all on the same page:

Originally Posted by Wiki_transformer_oil

Transformer oil is usually a highly-refined mineral oil that is stable at high temperatures and has excellent electrical insulating properties. It is used in oil-filled transformers, some types of high voltage capacitors, fluorescent lamp ballasts, and some types of high voltage switches and circuit breakers. Its functions are to insulate, suppress corona and arcing, and to serve as a coolant.
. . . The dielectric strength of new untreated oil is 30kV(rms) and after treatment it should be 60kV(rms).

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

[krousdb]

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.

[Winston]

Krous,

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

[Winston]

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?

[dryismyquest]

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.

[bwilson4web]

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

[hobbit]

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*

[Patrick Wong]

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.