Transmission fluid

There is no filter in the transaxle.
Toyota has no set oil change interval for the ATF WS, so you are free to make up your own.

I like 50,000 km, 150,000 km and then every 150,000 km thereafter. (much of the discoloration happens early)

 

Except for needing a long piece of tubing and a funnel to pour the new fluid from above, it's even easier than an oil change.

It's a good idea to break loose the fill plug first in the unlikely event that it's too difficult to remove. You don't want a drained transaxle only to find out you may not be able to fill it. Again, unlikely but why take the chance.

 

Bought my car new in 07 and have changed the trans fluid 3 times so far and I can tell you with great confidence that if you just change it once it will be good to go.
Once you get rid of the initial brake in wear in that fluid has shown very very low wear.

I always do that with a new car. Change the trans fluid and engine coolant at 10,000 it will greatly extend its life. That’s wear all the wear is. In a Prius the most wear is in the inverter coolant.

Your car is far from new and probably never had its trans fluid changed so will look pretty black very high wear.

 

I also recommend frequent changes early, 30,000 miles and 90,000 miles, then less frequent changes every 90,000 miles there after.

ATF is a complex mixture and I worry that some of it 'wears out' over time.

From Wikipedia, the font of all knowledge: "Modern ATF typically contains a wide variety of chemical compounds intended to provide the required properties of a particular ATF specification. Most ATFs contain some combination of additives that improve lubricating qualities, such as anti-wear additives, rust and corrosion inhibitors, detergents, dispersants and surfactants (which protect and clean metal surfaces); kinematic viscosity and viscosity index improvers and modifiers, seal swell additives and agents (which extend the rotational speed range and temperature range of the additives' application); anti-foam additives and anti-oxidation compounds to inhibit oxidation and "boil-off"(which extends the life of the additives' application); cold-flow improvers, high-temperature thickeners, gasket conditioners, pour point depressant and petroleum dye. All ATFs contain friction modifiers"

While the basics may last forever, I have my doubts that none of that breaks down over time.

 

ATF in a Prius need not be a complex mixture. It’s strictly used as a gl4 lubricant. The fluid I run has not one drop of any of the components you mention and it shows zero wear over 80000 miles on my car.
I have the UOA’s In the sticky’s to prove it. It’s basicly a manual gear box.

The g2 only requires one fluid change the initial removal of the break in wear.
My subsequent changes were basicly a waste of money. But it could be the fluid I used is doing a pretty good job.

The g3 has some really bad looking atf after break in.

 

Concerning the transmission fluid,... the Toyota spec WS oil is approved in part because it's non-conductive... and there are two electric motors inside the transmission running in that oil bath.

Related, side topic: visited Toyota dealers today to get a quote on transmission fluid change. One dealer gave a straightforward $145 quote, the other a jaw-dropping $255 quote based on a story about having to connect a computer and manage the oil refill based on temperature (!) Anyone else ever heard this story?

 

It comes up here with tiresome regularity.

I wouldn't pay over $100, in particular in US dollars. It's about the same amount of effort/complexity as an oil change, albeit a bit different: a simple drain-and-fill, and the car should be level when filling: when it starts coming back out the level is correct.

Up here the fluid is available at the parts counter for $9.14 CDN per litre, and four qts/liters are required. There's also a couple of washers that should be replaced, they're maybe $5 in total.

 

many Toyota trucks require the temp monitoring upon trans fluid change so that dealer is clueless.

Its strictly a dump and pump. All you need to do is clean the dump magnet..

 

Is there a way to check the current quality of transmission fluid or should I change the fluid based on my intuition?

 

After the first change, every 100,000 miles. Personally, I recommend 30,000 miles for the first change.

 

The important part of this chart has to do with the formation of varnishes. I have seen varnished fluid on many a Toyota. I guess if you spend time driving in a cool climate you may get lucky and have minimal varnish. Drive around in the desert and you will have a supply of varnish that is great for protecting furniture, but probably not so great in a transmission.

 

You would have to raise the car and remove the fill plug to check fluid condition. I would probably just change it if you don't have any record of it being done.

I change the fluid every 60k, it's just drain and refill. A prius trans doesn't get as hot as a normal automatic trans- so the fluid doesn't oxidize the same way. But since the prius trans has high voltage electric motor windings, it's not a bad idea to to dump the fluid every now and then.

Posted via the PriusChat mobile app.

 

My trans sure did have a high amount of varnish judging by the smell and color; it was no different than other non-hybrid Toyotas I've seen with over 150k mi.

On the 2nd gen, the windings are not in contact with transmission fluid.

 

correct.

 

I am not positive on that point. Section 7 of a Toyota engineering paper describing the refinements between the Gen 0 (Japan only) Prius and the Gen 1 (first to be introduced in the US), posted here, confirmed that there was a seal in Gen 0 to keep the oil from entering the motor / generator chambers, but that the seal was already done away with in the development of Gen 1. Instead, the resin used to coat the windings was changed to improve its resistance to whatever oil they were testing with (Toyota ATF T-IV was what originally came in the Gen 1).

I might not have guessed that the mechanical loss of a couple of oil seals would have been anything to write home about, but figure 18 in that paper suggests that with that and a couple of other changes, they reduced mechanical losses in the tranny by 40%.

 

Does that Toyota engineering paper mention something about the Gen 2 transaxle and whether or not fluid is in contact with the windings? I ask this because I remember something mentioned by the Weber Univ. automotive professor about the Gen 3 having more advanced cooling of the windings with fluid, but that the Gen 2 has dry windings.

 

If that paper had mentioned the Gen 2 transaxle, Encyclopedia Brown would have been able to tell it was a forgery, the same way he could with the Civil War sword where the engraving mentioned the First Battle of Bull Run.

So there are at least three cases: oil expressly kept away from the windings (Gen 0), oil not expressly kept away (after Gen 0), and oil deliberately directed at the windings to cool them (definitely by Gen 3; earlier?).

We know the P410 (Gen 3) is in the third category, because of this illustration found in this paper:



Sano, Shinya & Yashiro, Takahisa & Takizawa, Keiji & Mizutani, Tatsuhiko. (2016). Development of New Motor for Compact-Class Hybrid Vehicles. World Electric Vehicle Journal. 8. 443-449. 10.3390/wevj8020443

But it's worth noting what that paper is: it is a description of changes between P410 (Gen 3) and P610 (Gen 4). The change is that Gen 4 uses the oil pump to bring the oil to the windings. In Gen 3, it got there through being splashed up by the gears. Because the paper is focused on the changes between Gen 3 and 4, it doesn't say whether the old, gear-splash technique was only used in Gen 3. It simply calls that "the conventional motor cooling structure".

I haven't happened to find a similar paper talking about, say, the changes from Gen 1 to Gen 2. But in Prof. Kelly's "Deep Dive" videos on the P111 (Gen 1) and P112 (Gen 2) transaxles, the same oil catch structure is visible at 46:38 in the Gen 1 video and 27:18 in the Gen 2, and the same oil drain passage from the bottom of the MG2 stator area back to the pickup tube and sump area is visible at 25:35 for Gen 1 and 29:09 for Gen 2.

 

So does gen 2 transaxle have windings immersed in transmission fluid?