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The BIG transaxle hoax??

Discussion in 'Fred's House of Pancakes' started by Stevewoods, Apr 12, 2021.

  1. Stevewoods

    Stevewoods Senior Member

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    What I refer to below is replacing the fluid in what IIRC is the Prius transaxle. Thought about putting in the Care/Maintenance forum, but seems that one is getting a lot less eyes.

    So, after reading lots of posts about how important it was to replace the "lifetime" transaxle fluid in the Generation 2 prius, I did it at 50K and 100K.

    Have had no problems.

    The thing is, I just searched the web extensively and found that no one else has really reported problems, either. Since Toyota does not require/recommend it being replaced, I assume that most owners did not replace the fluid at all.

    Yet, I do not see any real reports of any problems.

    In other words, I think all of us that went a bit ballistic and replaced it, once, twice, or three times or more, wasted our cash.

    The reason I was thinking about this is because my Subaru dealer wants to replace the fluid in my Outback at 30K. I am thinking not.
     
    #1 Stevewoods, Apr 12, 2021
    Last edited: Apr 12, 2021
  2. ChapmanF

    ChapmanF Senior Member

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    The cost of stator replacements in a Prius transaxle has been motivating a lot of the fluid-change talk, though I think Carolyn Coquillette also ended up thinking the causality wasn't as well established as some were making it out to be (see 1:30 to 3:11).

     
  3. bisco

    bisco cookie crumbler

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    i think it started with fluid analysis
     
  4. Stevewoods

    Stevewoods Senior Member

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    Well, It's a Gen I, so not really a comparison with the Gen II.

    But, I do wish Carolyn and Luscious Garage were near me.
     
  5. bisco

    bisco cookie crumbler

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    you can't afford her
     
  6. Trollbait

    Trollbait It's a D&D thing

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    The fluid in the transaxle is the automatic transmission fluid that Toyota uses in many of their cars. As an automatic fluid it is engineered to lubricate and act as a hydraulic fluid to operate the transmission. Compromises were made to get that dual function. The one of most concern to us is in the fluid's heat tolerance. A basic automatic fluid starts breaking down around 200F. Synthetic fluids, which this is, can take higher temps but still not as robust as the oil in manual transmission against heat.

    The transaxle isn't an automatic; it doesn't need a lubricant that is also a hydraulic fluid. Why did Toyota use it then? My guess is the low viscosity meant better efficiency, but perhaps it was better suited to work with the motor's components than their manual fluid.

    Those that DIY fluid changes have reported that the old fluid had a burnt smell to it, which leads to the conclusion that the fluid is getting too hot. Since this isn't an automatic transmission, that may not be a bad thing as long as the fluid still lubricates. The fluid likely got thicker, which hurts efficiency, but most people don't change the fluid, and there hasn't been a higher than average transmission problems reported.

    Toyota did put a a transmission fluid cooler in the gen4. Something that all automatic transmissions already have. Perhaps burnt fluid was causing problems. Then again, markets where towing with a car is normal have been asking for a tow rating on the Prius for years.

    Personally, I'd change a lifetime fluid around 100k miles. 100k to 150k miles is generally what car companies consider a car's lifespan.
     
  7. Ronald Doles

    Ronald Doles Active Member

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    ATF in a regular transmission does double duty.

    One, it lubricates the bearings as well as the wet clutch packs. Material worn from clutch friction surfaces from each gear change ends up contaminating the fluid.
    Two, the torque converter generates heat in the fluid until it locks up. Under normal driving conditions, it usually locks up once the vehicle is in high gear minimizing fluid temperature rising.

    Towing is harder on the clutches due to more upshifts/downshifts which produces more clutch wear/contamination. With a heavy load, the torque converter spends more time unlocked and in lower gears and generates more heat. Fluid temperatures can get pretty high, especially in hot weather. Most standard vehicles offer a tow package to go with the trailer hitch which includes a transmission cooler. The cooler only takes care of the heat and not the additional contamination. Many service manuals recommend changing the transmission fluid more often if you tow regularly.

    The Prius fluid is just there as a coolant for the MG windings and to lubricate the gears and bearings. The largest source of contamination, the clutches, is absent.

    Not so sure about additional heat buildup from the MG windings if you attempt to tow with a Prius.
     
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  8. ChapmanF

    ChapmanF Senior Member

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    Maybe the Gen 4 thing is a more traditional-looking transmission fluid cooler?

    The earlier generations definitely had the coolant in the inverter loop pass through passages in the transaxle case to carry heat away from the oil, which is just on the other side of the aluminum in that same case.

    This pic of a Gen 3 or Prius v transaxle shows both the green area used for coolant heat exchange in both, and the purple area that is additionally used in the Prius v.

    [​IMG]
     
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  9. Travis Decker

    Travis Decker Active Member

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    Your Subaru has a failure prone transmission. Change it. Or learn about why modern subarus should not even be in the same paragraph as the most reliable cars ever built aka Prius.

    We see gen 1 and gen 2 trans failures, gen 2 seldom. Camry sometimes as well.

    It’s so cheap why wouldnt you do it on prius?

    Guess cheapest car to operate ever in history just makes people even cheaper?
     
  10. royrose

    royrose Senior Member

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    Officially, I believe Subaru says inspect the fluid at 30,000 miles but I would do it as well. Can't compare the brilliant simple Prius transaxle to complicated transmissions in conventional vehicles.
    I haven't done it in my 2010 with 101,000 miles and never will. It is not just money, it is time and effort as well. There is a long list of preventative maintenance that people do (and recommend as essential on this forum). It is a slippery slope that I prefer not to go on. I'm not putting many miles on it now, so whoever buys it cheaply at 12 to 15 years can do whatever it takes to keep it going longer. Yes, it's cheap so do it if it makes you feel better but don't suggest that others are negligent if they don't.

    If I ever get to 120,000 miles I'll do the EGR system when I am changing plugs. Other than that I follow the schedule.

    (Rant over)
     
  11. Mendel Leisk

    Mendel Leisk Senior Member

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    This is my go-to rationale; $40~ for supplies if you DIY. And an hour or two, mostly fussing with getting the car raised and level, and best to remove the underpanel.

    I’d do one early, around the 1 year or 10k mile mark. Then around 50k or 5 year. That’s probably enough.
     
  12. farmecologist

    farmecologist Senior Member

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    Me as well. Toyota doesn't recommend transaxle fluid changes for the Prius for the 'life of the vehicle'. However, our definition of the 'life of the vehicle' most likely doesn't match Toyota's definition. (y)

    Come to think of it, our 2010 is due!
     
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  13. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    Subaru manuals do list that the fluid should be 'inspected,' but what is apparently lost in translation is that much like any other inspection, if you do not find conditions to be adequate, you should immediately proceed to a remedy.

    This has come up many times on a few Subaru forums I follow. I think it's something cultural at this point. Americans read the directive to inspect, and they'll pull the ATF dipstick, see whatever they see, and immediately claim credit for having done the maintenance.

    Granted, Subaru could be a little more forthcoming with some sort of standard to look/smell/actually test for when pulling that dipstick, but the bottom line is that a CVT fluid drain & fill every 30k is a darn good idea for those cars.
     
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  14. bisco

    bisco cookie crumbler

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    has this proven to forestall failure? i think my daughter is nearing 30k on her subie. it's almost all highway at 60mph, if that matters
     
  15. Stevewoods

    Stevewoods Senior Member

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    I just talked to my "indie" mechanic, whom I have been using for a few decades. He has lots of experience with Subarus.

    He thinks the whole differential fluid thing is unecessary unless you are towing -- or if you have a very heavy foot on the accelerator -- meaning screaming starts from stops, slamming down the pedal on grades, etc.

    However, he DOES agree with the Subaru directive to change brake fluid at 30K -- at least in the Pacific Northwest. He talked about the fluid loving to asorb water, and yes, the system is supposedly sealed, but....

    Yesterday, I was leaning toward not changing the differential fluid in the Outback. Today....
     
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  16. Trollbait

    Trollbait It's a D&D thing

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    Today's automatics can lock up in lower gears for better efficiency. Tow packages generally have an extra transmission cooler added. If you do your own transmission fluid changes, putting in the extra cooler isn't hard. The difficult part is in routing the lines to the front of the radiator.

    The gen4 Prius is the first with an official tow rating in some markets. It is also the first to get a transmission cooler. Toyota apparently had concerns over the heat build up in the transaxle.

    That's what I assumed when the 'what's new' releases for the gen4 mention a cooler.
    Because to the Prius maintenance manual says nothing about changing the fluid in 120k miles.
    took a look at the 2010 Prius maintenance manual. Calls for an automatic transmission fluid inspect every 30k miles. At the end of the manual, this is described as just an inspection for leaks.
     
  17. royrose

    royrose Senior Member

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    I think people are talking about the CVT fluid, not the differential.
     
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  18. Mendel Leisk

    Mendel Leisk Senior Member

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    Our various automatic Hondas called for tran fluid change around every 30k, kms if I’m not mistaken. Not worthy of consternation or hand wringing: just do it.

    and with the Prius, as cheap and simple as it is: I don’t mind doing a transaxle fluid change or two, if only so I sleep better.
     
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  19. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    "proven to forestall failure" would be a pretty big claim. I don't think I can go quite that far for you. I can tell you that the Subaru CVT (all versions/generations) does rely on friction between parts, and employs a torque converter which means fluid pressure is what's pushing the car. Push harder and that fluid will get hot. It also employs a valve body with several electric/hydraulic valves.

    My last Subaru had the 5EAT transmission, not a CVT. This was a traditional epicyclic automatic with clutches, torque converter & valve body. And I can tell you that it absolutely gained a benefit from an ATF flush every 30-40k. It was pretty sensitive. It would shift a lot smoother with fresh ATF.

    What I've read of the Subaru CVTs is that they are even more sensitive to fluid quality, but this isn't firsthand experience.

    Can't speak for anyone else, but yes I'm saying that the CVT fluid should be replaced periodically and 30k matches what I remember.

    Differential oil? That's a whole different thing. I know Subaru has published a replacement spec but a lot of Subarus did 20 years on the road with factory diff oil. The thing to watch for is deep water- if the Subaru diff is submerged for more than a few minutes the oil will float out through the breather hole and leave the assembly un-lubricated.
     
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  20. bisco

    bisco cookie crumbler

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