ATF Change

Thanks for taking the sample. Clearly, it was time for a fluid change

 

I usually would not expect a transaxle fluid change to help mpg since used fluid has lower viscosity than new. However when I replaced the transaxle fluid in my HiHy I subsequently noticed an improvement in mpg which has been sustained, as much as 10%.

The factory fluid level was overfilled around 1 qt or so, and I attribute the mpg gain to reducing the fluid level to the correct amount.

 

Film strength tends to lessen as viscosity lessens. ATF is already on the edge when it comes to it's ability to prevent metal to metal contact. It's true that lower viscosity causes lower frictional losses from the oil itself, but that is wiped out dramatically once metal to metal contact starts occurring resulting in a dramatic rise in friction and temperature.

If you put just water in your PSD, the fuel economy would be awful for the few minutes it took to destroy it.

 

That's the problem once oil degrades, it can either shear out or can thicken dramatically

 

Nobody is asking about Redline D6? They make it for the Prius? I thought the Prius HSD oil was "special" due to the high voltage in that thing.

 

I'm not so sure about any special electrical properties. If you download and study the Oak Ridge Lab dissection of the Prius, the MG's appear fairly well sealed. Only special non-conductive oils can be used around transformers and motors. ATF would never be allowed in something like an oil cooled transformer, it would explode once you energized it

Toyota WS fluid has lower viscosity to work in their new automatic transmissions, such as the 5 speed auto in my FJ Cruiser. Other makers, such as GM, also have new specs for a low viscosity ATF

Amsoil does make an ATF that claims to be directly compatible with Toyota WS

AMSOIL - Synthetic Low Viscosity Automatic Transmission Fluid (ATL)

Although only a concern to those of us who live in Arctic conditions, note the ASTM D-2983 test, which is done at -40 C: 9,050 centiPoise. It's generally accepted an ATF should not exceed 50,000 cP at -40, if you expect reliable operation. I do believe I will use the Amsoil fluid this fall when I service my FJ auto again

Although the Prius cvt doesn't use torque converters, clutches, etc, it's nice to know that a substitute to WS provides very good low temp performance. Reduced friction at low temps will help fuel economy.

 

Elsewhere it is written that the MG windings are directly exposed to the ATF. If that is true there's no way to be certain how their insulation will react given long-term exposure to other fluids, so I wouldn't risk anything other than the recommended Toyota fluid. ORNL certainly won't pay up if the Toyota warranty is voided :_>

 

A picture is worth a thousand words...stator windings definitely exposed to transaxle ATF.

 

I've thought about this for a few years. Originally I accepted that the windings were immersed in the fluid, or at least exposed to it. I changed my mind when I realized that the large oil cooled transformers require a special non-conductive oil, even a trace of metal additive would cause an internal short and explosion

If the WS fluid was unique just to the Prius, I would accept the idea of electrical use. However, the same WS fluid is used in many Toyota automatic transmissions, such as the 5 speed auto in my FJ. A modern ATF has many additives, such as friction modifiers, to allow the clutches/bands to properly apply without slip or shudder

I have yet to uncover any convincing arguement that WS fluid has any special electrical properties, at least compared to conventional ATF's.

I looked around and came across these cutaway photos of the CVT case. It appears that MG 1 and 2 are sealed, but correct me if I'm wrong







That said, when you compare the cost of WS to fluids that claim to be WS-compatible, there is little to no cost savings using an alternate fluid. I changed the cvt fluid 5 times over the time I owned my 2004 Prius, the fluid was priced competitively

You can find generic Dexron fluid a lot cheaper, not sure if it would be appropriate for use in the Prius. A generic Dexron fluid absolutely WILL cause shift problems (Slip, shudder, etc) in a Toyota automatic transmission that requires WS

 

Hi Jay,

Pls see Florian Steiper's photos of a disassembled Classic transaxle that had failed:
ipernity: MG2 Disassembly by Florian

At least with this model, the stator windings are exposed to the transaxle fluid. Bits and pieces of plastic insulation (presumably from the windings) were found in the drain pan.

You'll recall that a PC member recently posted about his experiences replacing a 2G transaxle. Unfortunately he never got around to disassembling the failed component to see what it looked like inside.
http://priuschat.com/forums/gen-ii-prius-technical-discussion/58920-transaxle-failure.html

 

I clicked on the link you provided and I read about the Amsoil ATL. Towards the bottom of their page it states that it is not to be used in a CVT.

 

Florian's Classic didn't use WS, it used T-IV fluid. That would imply that both T-IV and WS possess special electrical insulating properties that no other ATF have, which I find a bit of a stretch

It could be that Toyota tested the wire/winding insulation specifically with T-IV and WS, to determine compatibility. That is, the insulation material was designed specifically for exposure to T-IV and WS

However, if there is a compatibility issue, those with second generation Prius running an aftermarket fluid, like Redline D6, would have experienced issues rather quickly. The insulation should have broken down and failed

I personally would not use an aftermarket fluid in the case, simply due to there being no significant cost savings or convenience. The WS is pretty easy to find at a dealership, and priced similar if not a bit cheaper compared to the aftermarket Redline and Amsoil products

I'm unsure if anybody has determined whether generic Dexron is useable. B Wilson had some higher wear metals with AMsoil, if I recall

 

No Amsoil fluid is compatible with "conventional" CVT's, as they cause slip in cone/belt style CVT's. Redline does make an ATF compatible with such cone/belt style CVT's. We do have forum members running Redline D6 in their PRius, apparently with no ill effects

Mechanically, the Prius CVT is extremely simple, with gears and a transfer chain. Four wheel drive transfer cases have used ATF as a fluid for decades, with similar transfer chains and no wear issues.

As I stated above, I would still run WS in the case, as it's the only approved fluid, is easy to find at a dealership, and costs about the same if not a bit cheaper than synthetic alternatives

 

Oh, I doubt it will kerplode or anything like that. We already have some forum members using "non approved" cvt fluids.

Compared to other ATF's, is there anything special regarding electrical conductivity with Toyota T-IV and WS fluids? Both of these fluids have had to work in the lineup of Toyota automatic transmissions, which means they had appropriate additives and friction modifiers to prevent slipping/shudder with the clutches and bands

It's entirely possible a generic $2 a quart Dexron compatible fluid would work fine. However, cost vs benefit is difficult to argue, as you could potentially destroy $4,000 worth of components

 

At any rate, it's not the insulating properties of the oil that's important. In the HSD we have about 550V peak. If you want to compare that to a "service transformer" that you see on poles and in metal boxes at the side of the roads in subdivisions, they run a -minimum- of 5600 V peak (4 kV RMS).

I suspect the only problem could be the effect of the oil on the insulation and wire tieing parts. This can be a little easier to evaluate. Just take some of the oil and immerse "magnet wire" and wire ties in it and heat it up to about 100C (the HSD never gets this hot). See if it causes the insulation and ties to get brittle.

I suspect the lubricating properties are superior with the synthetic oil.

The other thing to think about is how clean the oil remains. There are needle and ball bearings in there, and they need -CLEAN- oil, not necessarily lots of oil.

I thought the WS was "semi-synthetic"? At least I thought I read that somewhere.

 

David, I like the premise of your test, but in practise I'm not sure if it would have meaningful results

We really don't know what the composition of the M/G winding insulation is. I do know that for oil cooled transformers, eg GE and Siemens, there are different specs for the insulation material, and different specs for oil quality, circulation, testing, etc