Transmission/Transaxle Fluid Replacement ?

[TexomaEV]

Folks, is there a filter that needs to be replaced when doing a transfusion of transmission fluid on a 2001 Prius?

Also, is there a magic synthetic, super slick fluid one would recommend or additive over just the OEM fluid?

Thanks in advance. I'm not sure if the fluid has ever been changed, so I figure I'd be safe rather than sorry.

[bwilson4web]

Hi,

Originally Posted by TexomaEV

Folks, is there a filter that needs to be replaced when doing a transfusion of transmission fluid on a 2001 Prius?

Also, is there a magic synthetic, super slick fluid one would recommend or additive over just the OEM fluid?

Thanks in advance. I'm not sure if the fluid has ever been changed, so I figure I'd be safe rather than sorry.

No filter but I'd recommend getting a replacement gasket and drop the pan and wipe it down. Regardless, here are my 'lessons learned':

• 2003 Prius - Cold Weather and Transaxle
• 03 Prius Transaxle Temperatures
• Prius Type T Oil Analysis

I'm currently running a test with Type WS, the OEM is Type T-IV. Due to the high levels of Cu, I can not recommend Amsoil ATF.

Bob Wilson

[adric22]

Yeah, I changed the trans fluid in mine when I got it too because the previous owner had never done it, along with the coolant, oil, spark plugs, air filter, and cabin air filter.. You might want to check that cabin air filter.. It is behind the glove box and easy to reach. The thing was horribly disgusting, full of dead bugs and little twigs and leaves. That is the air you are breathing in the car! However I chose not to change the inverter coolant because it looked okay and the process is more involved for bleeding the air out of it.

[TexomaEV]

Thanks, that's quite some testing you did there on the different fluids. I'll prob stick with the OEM, and clean out the pan as you stated. Local transmission shop, said they'd be happy to do the work, and learn a little about a Prius at the same time. Just wanted to ask you experts before hand, and now I can give them a heads up as what to do/expect.

[jk450]

Originally Posted by TexomaEV

Folks, is there a filter that needs to be replaced when doing a transfusion of transmission fluid on a 2001 Prius?

To begin with, your transmission does have a filter. I'm not sure why you are being told otherwise. It's a metal screen that is held in place by a plastic housing on the end of the oil pickup tube that extends into the transmission fluid pan. With the pan off, it's easily visible.

While the filter is replaceable, there is no replacement interval, as it can be cleaned. It's nice to wipe out the pan if it's been removed, but it's more important to inspect the filter screen and make sure it doesn't have anything clogging it up. Most of the time, it's fine.

Originally Posted by TexomaEV

Also, is there a magic synthetic, super slick fluid one would recommend or additive over just the OEM fluid?

No. OEM fluid is Toyota Type T-IV. The later WS fluid has improved cold temperature viscosity, according to Toyota, but Toyota says the two are not compatible. About a tenth of the old fluid remains in the transmission during a fluid change. However, some folks replaced their T-IV with WS years ago, and I have heard of no issues related to the fluid change.

[bwilson4web]

Originally Posted by jk450

To begin with, your transmission does have a filter. I'm not sure why you are being told otherwise.

There is a difference between a pickup tube screen and an oil filter. If you replace it, you'll need a new O-ring too. The common meaning for a filter is a trap to capture debris in the oil between changes. Regardless of what it is called, the pickup tube has a single layer, fine plastic mesh to keep chunks out of the oil pump. There is no transmission filter like the kind found in automatic transmissions. The gunk laying on the pan is the part that can be removed.

Doug was a pioneer in putting in an after-market, transaxle, spin-on oil filter. However, I understand it was removed later.

In open-pit mining, earth movers and heavy dump trucks often use a by-pass oil filter system to remove the smallest particles. It runs in parallel to the existing oil filters. Reports are these micro-filtration systems can triple the oil change interval but those vehicles are running 24x7 in terrible conditions. The oil and equipment savings more than paying for the by-pass filter system.

BTW, I've kept all of the oil sample tests and photos over in "Prius_Technical_Stuff" . . . if you want to get in the fine details. <grins>

Bob Wilson

[jk450]

Originally Posted by bwilson4web

There is a difference between a pickup tube screen and an oil filter.

The screen is a filter. That is its sole purpose.

[bwilson4web]

Sorry but a filter removes wear materials by trapping it so it can be removed with the filter. A screen simply keeps the chunks from going in to damage moving parts. These chunks often just fall down off the screen when the flow stops.

Originally Posted by jk450

The screen is a filter. That is its sole purpose.

Semantics by any other name is still a waste of time.

There is no replaceable filter like one would find in a traditional, automatic transmission. The wear materials form a gunk layer on the bottom of the pan and it is important to wipe it clean. Note that the NHW20 and ZVW30 do not have a transaxle pan.

BTW, if the oil change test results indicate there is significant carry forward. I'd recommend having a clean, dry, capture bottle, say a former water bottle, and saving a sample from the drain. If it looks like testing may be warranted, you'll have a sample to send to a service. Typically you'll want a standard oil test along with viscosity at 40C and 100C, which should also give the oil viscosity index. This is your primary 'health' indicator.

If the used oil tests particularly bad, you might consider treating this first one as a flush and changing it again in a couple of thousand miles. The cost is modest and you'll take out risk factor.

Testing the gunk in the bottom of the pan is possible and if you see something looking bronze like, may be something to consider. My oil testing service used the kitchen paper towel material to do a microscopic analysis. As for other pan debris, you may see some white, faintly pinkish bits. Those appear to be aged transaxle case sealant. We're finding the sealant is the primary source of excessive Si in the test results.

Bob Wilson

[jk450]

Originally Posted by bwilson4web

A screen simply keeps the chunks from going in to damage moving parts. These chunks often just fall down off the screen when the flow stops.

Unfortunately, this is incorrect, as well. The material that one will find in the bottom of the pan is, for the most part, too fine to be filtered by the screen. The material that is filtered by the screen almost always sticks to the screen.

If enough material collects, it can reduce the flow rate of the pump, which can in turn lead to transaxle failure. That's why it's important for the technician to take a quick look at the screen with the pan off.

[tochatihu]

The external add-on filter Bob referred to was an off-the-shelf fuel line filter, with a pore size probably on the order of 50 microns. The fluid pump was re-plumbed by a Toyota Mechanic in Olympia WA to have a loop external to the transaxle case.

I ran it that way for about 20 k miles. On inspection, the plastic case of the filter had been deformed by the about 80 oC fluid flowing through it. On that basis I deleted the filter but left the external-flow loop in place. The filter had not collected much particulate matter at all; this 2001 had already had 3 fluid changes @100 k mile.

We reckoned that there was not much to be gained by filtering to this cutt-off, vs. the ca. 1 mm (1000 microns) installed pickup screen. The pan magnet does a fair job of collecting ferrous particles, and non-ferrous settle in the sump. Transaxle fluid pumping is by no means as vigorous as that of engine oil, so that settling is not much disturbed.

I guess that Toyota (USA) never did recommend transaxle fluid changes on NHW11 (can't testify to later Prius gens), but at least a few participants in the internet groups have been recommending it as preventative maint. for a long time.

Mostly unrelated, I killed a Honda engine by allowing accumulation on its engine oil pickup screen, hence this has been a matter of personal interest since. Never again