Should I change the transmission fluid at 25K/3 years of ownership, or not?

There is a good argument for changing it at 30k miles or even earlier the first time. There are more metallic particles from early break-in wear and the Gen III doesn't have transmission filter. IIRC, Bob Wilson posted some useful transmission oil UOAs with particle counts a year or two ago.

OTOH, if you wait until 60k, you will still be taking better care of it than most people.

I was taking a look at UOAs and they did make me want to change the fluid but I'm still not totally certain that I will. When I asked about it at the service department they looked at me like I was crazy, but who knows. Bob Wilson lives in the same city as I do. Maybe I'll have him help me out with the change, or get the dealer to do it. I just don't want to mess anything up myself, or have the dealer make a mistake either on a vital part of the car. I'm a little intimidated even though the process doesn't seem too difficult. Thanks for your input!

Gents,

Before a few months ago, I would have been in the camp not to change the fluid early. I've always been a guy who follows the maintenance schedule which is generally conservative. But a few months ago our Mazda minivan began having transmission problems at 68,000 miles. While driving on the freeway it would slip (if that's the right word) from drive to neutral. Took it to our mechanic and they changed the transmission fluid then test drove it, and said the transmission appeared to be OK. They also said we should have changed the fluid long before now (although according to the maintenance schedule it wasn't due until something like 120,000 miles).

We felt like we dodged a bullet but then last week while parked in our driveway it slipped from park into neutral! (I don't have all the details - it's my wife's van and I wasn't there). It has happened twice.

I can't help but think that if I had changed the transmission fluid at say, 30,000 miles, these problems may not have happened. Now, I understand that's there's no proof that having changed it earlier would have prevented this problem. I get that. But when you're faced with a very expensive transmission repair bill, it makes you stop and think that maybe the manufacture was wrong not to recommend an earlier transmission fluid change.

Tomorrow I'll have had my Prius for two years, and I'm just about at 30,000 miles. I'm strongly leaning towards getting the transaxle fluid changed, in the hopes of preventing a similar outcome. I know if I don't it's unlikely that I will have a transmission problem, but again, when you experience this type of thing it makes you think that a little prevention goes a long way.

It's all part of growing up. Eventually you find out cops lie on the witness stand, car service writers try to sell you services you don't need and self serving manufactures tell you not to get all the services you should get.

For some reason most manufacturers overstate how long you should go between transmission fluid changes.

I've been wondering about their motivation for that. I'm sure it involves money, somehow. Improves the vehicle's low maintenance status?

FWIW, a transaxle fluid change is pretty straightforward, cheap insurance. A little different than an oil change, the fluid a little pricier. The fill hole a little harder to access. And there's a stipulation that the car be level when re-filling, so typically a DIY'r needs to have the whole car raised, a bit. That's about it.

IMHO, just change it at the end of the first year of ownership, then bi-yearly thereafter.

Where's that stated?

I think the low maintenance is part of it. I think the biggest part is what is one's definition of "lifetime". I think it was mentioned in another transmission fluid thread that the fluid was good for the lifetime of the car.

Toyota's definition of "lifetime" might be 125,000 miles. Your definition might be 250,000 miles.

The real key here, and it is not being well debated that I can see, is what do the fluid analysis results show for the transmission fluid? From what Ed is showing, it makes a LOT of sense to change the fluid at 25,000 miles (I changed mine at 35,000 miles, and only because I read it on this site. I wished I had changed it sooner. I will have it changed again at 60,000 miles.

When I had my oil changed at 40k, I had an analysis done at Blackstone Labs. They said that I still had useful life left in the oil and I could try going 12k miles between changes. What this told me was

1) 10k oil changes, for my driving style/commute is adequate.
2) If I opted for 5k oil changes, I would be wasting resources (oil, money, time).

Had the analysis come back saying I was at the limit of the oil's lubricating properties, I'd adjust my oil changing schedule to 7.5k.

Actually pretty obtuse: the Repair Manual says prior to checking level "Stop the vehicle on a flat road".

Looking at the picture (looking towards driver's side, front of car on right), it seems to me if just the front end was raised the fluid level would be inaccurately high.



Addendum, I think too the Repair Manual makes the assumption the reader is a dealership mechanic, using a full lift, level by design.

But Ed does not determine the minimal requirements for the TA fluid, toyota engineers do. Oil analysis is meaningless if the degradation of the fluid is accounted for in engineering(which it obviously is). if it makes a LOT of sense to do it, why doesn't toyota even recommend checking it? why don't they provide a means of checking it?
The real key here, being completely overlooked, is "there is no incidence of fluid related failure established for gen III transaxles at 100, 200, 250kmi." once again we are in the realm of recreational tinkering.

It's just baffling that an owner, doing analysis on his one vehicle, thinks he's discovered some real deficiency in Toyota's engineering, with millions of vehicles in their dataset. And that these owners believe that Toyota thinks there's profit to be made in claiming "no maintenance transaxle" over the customers lost when transaxles fail at 150kmi.

So, again, let's summarize:
There is no documented incidence of fluid related failures in Gen III prius transaxles.
There is no demonstrated benefit for early fluid swaps.
IMO there is greater risk of costly repair from owner error on this particular fluid swap than risk of a fluid related TA failure collectively.

I would assume that Toyota engineers are given a target lifetime for the component and have given instructions on how to hit that target.

I don't know what that target lifetime value is. Do you know what that target lifetime value is? Is my definition of "lifetime" different than their definition of lifetime.

To me, this might be an ounce of prevention. To you, this seems to be curing the disease by killing the patient.

I believe the schedule calls for inspecting the fluid every 30,000 miles. The means to do so are the fill and drain plugs. One can check the level, the smell, and the color of the fluid via the fill plug, and pull samples via either plug, I suppose.

What has been found leads some of us to change the fluid. If you prefer not to inspect your fluid and not to change your fluid, go for it.

I changed my transaxle fluid at 25k miles and just changed it again at 50k miles. I plan to keep my car for many years and see this as an ounce of prevention and cheap insurance. The fluid was just as dark at 50k as it was at 25k compared to the light pink of the new fluid. Pretty much like edthefox5's pictures.

I will continue to change mine at 25k intervals. It takes 30 minutes and about $35 worth of ATF-WS fluid. It gives me complete satisfaction and peace of mind to do this. I could care less what Toyota's recommendations are or what others think.

Their definition of "lifetime" of this vehicle is certainly the target service life of the inverter and the battery. it does you no good to have the healthiest TA on the planet when the inverter and/or battery reach the end of their service life. By the time these components reach the end of their service life(let's say 12yrs 250kmi), their replacement will equal the value of the car.

You seem to have a lot more confidence in Toyota's engineers than I do. Granted Toyota has some of the most reliable vehicles on the road, including the Prius. The Toyota recommended maintenance is the "minimum" required to meet their warranty terms and I am sure some "lifetime" definition. I doubt you will find a Toyota engineer that would tell you that additional maintenance above and beyond their recommendations is a bad thing or waste of money. In fact most dealer service departments make a lot of money off of convincing people of the "additional" maintenance needs such as fuel flushes, brake system flushes, etc.

As for the transaxle, it is just as much a part of the "hybrid" system as the inverter and battery with the electric motors inside. You can choose to do only the recommended maintenance or you can choose to be proactive and do additonal preventive maintenance. I choose the latter.

As far as the inverter and the battery there are additional maintenance items that you can perform to enhance the life of this equipment also:

Inverter - Electronic inverter equipment today is very robust. The worst enemy is heat. You can change out the inverter coolant on a more frequent basis and monitor the turbulence in the coolant reservoir to verify good coolant flow. You can also monitor inverter and coolant temperatures with a ScanGauge or other device.

Battery - Once again heat is probably the battery's worst enemy. Keep the cabin as cool as possible to keep the cooling air to the battery as cool as possible. Check and clean the battery fan to make sure it is not being clogged with lint, dog hair, etc. You can also monitor the battery air flow temperatures and battery module temperatures with a ScanGauge or other device.

You do your maintenance your way and I will do it my way and I would love to get back with you at 250k miles and compare notes.

Yet according to reports here, Service department employees, despite profiting from this service and parts for DIY'ers, routinely (if not unanimously) advise AGAINST early TA fluid swaps.

I doubt you will find a Toyota engineer that would recommend changing fluid at 30k mi...so now we need a toyota engineer. If toyota doesn't think it's a waste of money, why don't they recommend it, and profit from it?

The only reason that my service advisors can give me for not recommending a transaxle fluid change is because it is not on Toyota's recommended maintenance list. When I ask them why they recommend all of the other additional flushes, etc. that are not on the maintenance list I just get stuttering and stammering

Maybe we have a Toyota engineer lurking on this site that can help us out here?

The interval quoted most often comes from my 225,000 mile, 8.5 year (so far) analysis of used ATF in my 2004 Prius. The first lab results at 61k miles showed that the ATF was used up and had an excessive metallic load. The second test after the freshened ATF had another 60k miles was better as the transmission metallic parts had "lapped in". The third at 180k miles was even cleaner. After a group of experienced Prius owners (including several engineers) evaluated this data, we decided that the "wise" protocol for a Gen2 or Gen3 Prius would be an early drain and refill of the Toyota Type WS ATF at about 30k miles and repeat the process every 60k miles thereafter (my dealer charges me $100). One of the more conservative group members has chosen to halve those intervals, but that seems a bit excessive to me.

JeffD

255,300 miles on my '05 and I have the ORIGINAL Transaxle/Transmission fluid and would have the same coolant if it weren't for the recall work (done at 220k miles). 5000 mile oil changes and tire rotations and still 47 miles per gallon. Oh yeah, and original batteries too! Drive on!

I just checked mine i had the car on a slope then used ramps to try and level it out. But the front end was still higher than the rear. It was about an 1/2 inch below the fill plug threads. So do you guys think mine is low on fluid? I'm going to not drive it untill i can get a bunch of fluid and jack stands and just change it. Also i see the fill plug on the picture is the plug thats lower the drain plug?

The spec for the fluid level is 0 to 10 mm or 0.39". If yours is really 1/2" then it is low but I suspect it was due to the car not being level.

The plug shown in the drawing is the fill plug. The drain plug is at the very bottom of the transaxle and is much lower than the fill plug. The big circle next to the fill plug is the axle connecting to the passenger's wheel. You can tell the fill plug since it will be just to the left of the axle and CV joint.

Good luck with the drain and refill.