5th gen prius 0w8 vs 0w16 discrepancies

Discussion in 'Gen 5 Prius Technical Discussion' started by 2023p, Dec 23, 2025 at 6:59 PM.

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  1. 2023p

    2023p Member

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    I think this was mentioned in a thread before. Dug deeper and called Toyota Of America. Apparently the 26 engine is identical, of course, to the 23 engine.

    Although the 26 engine verbage in the manual clearly states 016w may be used for one cycle and then immediately go back to 0w8 consistently.

    Strange. Seems to be begging for a larger issue, even if possibly only technical.

    Apparently the same engine on non north American sold vehicles with this engine, Prius 5th gen.. always recommended and requires(?) 08w oil, as per the manual. And for the 26 they finally updated the verbage.

    I don't want to be putting in the wrong oil due to some timing and certification North American issue.

    thoughts?

    I understand one can change their own oil etc

    hmm
     

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    #1 2023p, Dec 23, 2025 at 6:59 PM
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  2. BiomedO1

    BiomedO1 Senior Member

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    In the early days; 0w8 was hard to come by and most dealerships dumped 0w16 in.
    My advice is if the car engine was broken-in with 0w16, stick with it. The same engine in other countries go as high as 5w30. Switching to thinner oil after break-in may cause issues (ie. higher engine oil burn between oil changes). Some OEMs claim that burning a quart every 5K miles is acceptable - I don't!!! That much oil burn would kill the CAT, just outside federal warranty. Then again, that's all the dealership is concerned with - getting past the warranty period.

    Just my two cents.....
     
    #2 BiomedO1, Dec 23, 2025 at 7:37 PM
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  3. KMO

    KMO Senior Member

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    The 2026 engine isn't 'identical, of course'. How can you conclude that? Do you think a production line that can change which oil they put in and which oil sticker they apply can't change anything else?

    There is at least one potentially related change I've spotted in the technical manuals, which is that the oil level sensor was deleted in July 2025. Maybe it didn't like 0W8?

    (Another change at the same time, probably unrelated and due to new CARB rules for 2026 models, was the removal of charge mode for American PHEVs.)

    The Prius oil change to 0W8 happened worldwide at the same time, aligned with those July 2025 production changes. Whoever said European cars were using 0W8 before was referring to other models.
     
    #3 KMO, Dec 24, 2025 at 3:40 AM
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  4. Gokhan

    Gokhan Senior Member

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    And Gen 4 also switched from SAE 0W-20 to SAE 0W-16 in the 2020 model year.

    Did the engine change in Gen 4 or Gen 5 that allowed a lower viscosity grade? Snowball-in-hell chance. OEMs don’t spend that much thought on minute details of engines to recommend an oil viscosity. They make general tests, even on a slightly different engine, and then make recommendations for similar engines.

    What happened was basically that they determined that 0W-8 was safe after new tests, and then they changed the oil recommendation after that determination. You can use 0W-8 for earlier Gen 5, yes, without any problems.
     
    #4 Gokhan, Dec 24, 2025 at 4:00 AM
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  5. VelvetFoot

    VelvetFoot Active Member

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    Not sure what that tech manual is, but the 2026 owner's manual still makes mention of it on page 482.

    upload_2025-12-24_7-27-51.png
     
    #5 VelvetFoot, Dec 24, 2025 at 7:27 AM
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  6. KMO

    KMO Senior Member

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    I know it's still there in the user manual, but it's shown as a change in the parts catalogue and diagrams ("from 07-2025"), including new part numbers for every variant of the dashboard that gets the sensor signal (and there were a lot before).

    It's fairly common for out-of-date text to be left in manuals - if you see a conflict it's sensible to assume the new text is right, and the old text is no longer correct.

    And maybe it can still display that message, inferring it from other sensors?
     
    #6 KMO, Dec 24, 2025 at 8:03 AM
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  7. VelvetFoot

    VelvetFoot Active Member

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    I did a search for my VIN on the Toyota site and came up with this.
    Part 89491 in the diagram below.
    Mfr date of my car is Sept '25.
    I looked, and I think an under car plastic cover has to be removed to view.
    That's not going to happen for a while, lol.
    Maybe I could stick my hand down there holding a camera....
    upload_2025-12-24_9-0-8.png
     
    #7 VelvetFoot, Dec 24, 2025 at 9:05 AM
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  8. VelvetFoot

    VelvetFoot Active Member

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    I managed to get the picture below.
    It looks like a dummy plug to me-no wires.
    upload_2025-12-24_10-59-35.png
     
    #8 VelvetFoot, Dec 24, 2025 at 10:59 AM
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  9. 2023p

    2023p Member

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    Toyota of America - on the phone - said the engines are identical. Mayne they are wrong, hmm? Want to share the evidence?

    infact, every non north american 5th gen prius from day one called for 08w oil.

    when the 5th gen prius launched there, the manual and the oil cap both said 0w8. the engine is the m20afxs and it is identical worldwide.

    the proof is in the global part numbers. toyota uses the same oil pump and the same engine bearings for a prius sold in tokyo as they do for one sold in los angeles. japan has had 0w8 at every gas station since 2020, so they never had to "ease" into it like the west did.

    north american manuals only mentioned 0w16 because 0w8 wasnt in us warehouses or certified legally yet. everywhere else, 0w8 was the standard from the first car off the line, and still is.

    the japanese proof?

    toyota japan launched the 5th gen prius (model code x60) in early 2023. the official japanese owners manual lists 0w8 (jaso glv-1) as the standard factory fill.

    toyota developed 0w8 specifically for the japanese market years ago. they officially published the technical engineering paper for it in 2020 (sae paper 2020-01-1425).

    by the time the 5th gen prius arrived, 0w8 was already the default oil for the m20afxs engine in japan.

    the european proof?

    toyota europe and toyota uk released the 5th gen prius exclusively as a plug in hybrid. the technical press packs and manuals from launch confirm the use of ultra low viscosity oil.

    european manuals state 0w8 is the best choice for fuel economy and cold starts.

    because europe and japan already had 0w8 on store shelves, they didn't need to put 0w16 on the oil cap as a "temporary" fix like they did in the united states.

    why the us was different?

    the only reason north american manuals mentioned 0w16 at launch was because the american petroleum institute (api) had not yet finished certifying 0w8 for us sale. the car was ready for 0w8, but the american oil companies weren't.

    every 5th gen prius engine is built in the same factories with the same clearances. since those factories are in japan, every single one was filled with 0w8 before it ever touched a boat.

    edited for grammar, woops
     
    #9 2023p, Dec 24, 2025 at 2:37 PM
    Last edited: Dec 24, 2025 at 2:49 PM
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  10. Gokhan

    Gokhan Senior Member

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    OK, the reason for the removal of the oil-level sensor is nothing but cost cutting then. Don't get mad at me, but the reason for the cost cutting is Trump tariffs, you know. LOL
     
    #10 Gokhan, Dec 24, 2025 at 3:18 PM
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