5th gen prius 0w8 vs 0w16 discrepancies

Discussion in 'Gen 5 Prius Technical Discussion' started by 2023p, Dec 23, 2025.

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  1. 2023p

    2023p Member

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    I hear you and can see where the confusion (my errors and Toyotas show regarding all this) or misunderstanding is rooted.

    the 5th gen prius (engine) was engineered/designed for 0w8 oil. it also left the manufacturing plants filled with 0w8 oil.

    when i initially said other regions called for 0w8, i was referring to the factory fill engineering standard used at the plant in Japan.

    however, when looking at the printed manuals themselves (the physical books in the glovebox), you are correct: Toyota of Europe and Toyota UK, Japan also listed 0W-16 for the earlier runs.

    with that Even in Toyota's home market, the nationwide infrastructure for 0W-8 (JASO GLV-1) was not fully "universal" across every small-town service center at the exact moment of the 2023 launch.

    To ensure no owner was left without a service option, Toyota Japan printed 0W-16 in the manual—even though the engine designers had already finalized the car for 0W-8. They did the same thing NA did initially, it looks like.

    this is where the "lie/hedge/misinformation" becomes obvious. on many of those early 2023 Japanese units:

    the owner's manual said 0w16

    the oil fill cap on the engine said 0w8

    the radiator support sticker said 0w8

    this shows that the manufacturing plant in japan was building a 0w8 car, but the documentation department was still playing it safe with 0w16.

    what a country or region decides and then updated environmentally/certification wise and how a car manufacture navigates that is one thing.

    what this car and this engine are and were designed and manufactured specifically for oil wise, is another.

    that's the end of it for me.

    the roots and the fruit have been made clear, for me. the bruises and imperfections of finding clarity on it is par for the course. pretty simple.

    enjoy!
     
    #21 2023p, Dec 27, 2025 at 1:31 PM
  2. KMO

    KMO Senior Member

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    I know you really want to win your argument about it being okay to put 0W-8 in the car.

    And it's probably true that it is okay - that was widely surmised when the Prius first came out, given that other models with M20A-FXS were already specced for 0W-8, and it's even more likely now that they've changed to 0W-8 for the Prius since July 2025, with no obvious design changes, aside from the oil level sensor removal, which could be coincidental.

    But that's no reason to keep making stuff up. You've got a reasonable claim based on the engine type, but it doesn't help your credibility to invent things about the Prius production.

    The manuals and labelling for Japanese and European cars all said 0W-16. There's no evidence of 0W-8 ever being part of Prius production until July 2025 (aligned with the US 2026 model year).

    I know about the European labels myself, having one, and I just spent some time browsing Japanese YouTube for a shot, here:

    upload_2025-12-31_13-42-31.png


    And sure, maybe the car could have been filled at 0W-8 at the plant, despite all documentation and on-car labelling saying 0W-16, but there's no evidence for that. It could also have been filled with 5W-30, right?

    The pre-2025 English and Japanese manuals do specifically say, "SAE 0W-16 is filled into your Toyota vehicle at manufacturing" (and "0W-16 は、新車時に工場充填されている推奨オイルであり"), so you're making a claim that the documentation is actually false, with no evidence.

    Personally, if I had to guess, I'd say that they were being cautious about the use of 0W-8 in PHEVs - they may not have had enough experience with it to see if it coped with the sort of short cycles it might get, so they wanted to stick with the 0W-16 they had more experience with, at least for the PHEV. And then to simplify the Prius production, both HEV and PHEV got the 0W-16, rather than using different oils for the two variants on the line. And then few years later they'd managed to do enough testing with 0W-8 to be happy with it.
     
    #22 KMO, Dec 31, 2025 at 6:53 AM
    Last edited: Dec 31, 2025 at 9:51 AM
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  3. KMO

    KMO Senior Member

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    Above pic was from here, btw. A two-and-a-half hour review video :confused:

     
    #23 KMO, Dec 31, 2025 at 7:18 AM
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  4. 2023p

    2023p Member

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    Weird. The cynicism and presumption you seem to be projecting is... strange. Truth and facts don't need affirmation. They aren't an argument, they are not up for debate.They remain true no matter what anyone does, feels, presumes or thinks.

    Win? Such a curious lens to approach discourse and reality with. I hope you continue to feel like a winner. Enjoy!

    SAE 2020-01-1425, where Toyota engineers specifically developed 0W-8 for the M20A engine family years before the 5th Gen Prius was even revealed. To cite a manual as proof of engineering intent is a logical fallacy; manuals are marketing and service documents, not blueprints. The physical bearing clearances of the M20A-FXS remain constant globally, yet the oil recommendation changes by region. That isn't 'caution' ... that's a supply chain compromise

    In plain English, the 0W-16 oil recommended in your 2023 manual lacks the specific chemistry Toyota's engineers designed to protect the M20A's tight clearances. By using 0W-16, you are essentially using "yesterday's tech" in "tomorrow's engine."

    In short, it's not just okay to use. The engine was engineered for and filled with 0w8 in Japan. Nothing you or I say, presume, feel will change that.

    Perhaps once Toyota is forced to correct their mistakes/choices on this you'll understand better.

    Thanks, and please keep your argumentative approach focused on people that want to argue with you.

    Otherwise, you're just harassing people.

    I'm not arguing with you or anyone else, I shared reality, truth and facts, albeit with human imperfection. Truth doesn't need to win. Winning doesn't define truth. Someone can feel like they win or that it's a game and still be wrong. Hence, truth.

    This will be my last response to you.

    Physics and facts, not feelings and gaps.

    Please just stop. ♥️
     
    #24 2023p, Dec 31, 2025 at 2:44 PM
  5. 2023p

    2023p Member

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    Respectfully, for or anyone truly and solely interested in the actual discrepancies and the ultimate point:

    Observation bias won't change the engineering reality.

    Manufacturing labels and manuals are legal and logistical documents... they are designed to reflect what a company can support in a specific market at a specific time.

    They are not engineering blueprints.

    The physical clearances in the M20A-FXS don't change because of a sticker or a regional print run.

    Toyota is already in the process of aligning their global guidance for this engine as infrastructure catches up. You'll see.

    Not here to 'win' a debate or convince anyone to change their oil.. Here to ensure the full context is on the record for 2023 (etc) owners.

    Enjoy the car!
     
    #25 2023p, Dec 31, 2025 at 3:04 PM
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