No "how-to" head gasket posts for a Gen4?

Discussion in 'Gen 4 Prius Care, Maintenance and Troubleshooting' started by C Clay, Jul 26, 2026.

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  1. BiomedO1

    BiomedO1 Senior Member

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    So you at least have a cross-leak between the coolant and engine oil passages. If that cross-leak was at the head gasket; you should be able see the tracing/rupture on either side of the head gasket. If you don't; the cross-leak is someplace else.o_O
     
    #41 BiomedO1, Aug 12, 2026
  2. Mendel Leisk

    Mendel Leisk MMX GEN III

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    All the 3rd gen owners got to be guinea pigs for Toyota, and the reward was to "pound sand".

    The red stuff on the head gasket is a coating, not loose? Wouldn't be a stop-leak product?
     
    #42 Mendel Leisk, Aug 12, 2026
  3. GLCReviews

    GLCReviews New Member

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    2016-2018 were the primary years for that. By 2019 (not sure what production date month maybe) they should have all been remedied by then. But YMMV as usual.
     
    #43 GLCReviews, Aug 12, 2026
  4. Mendel Leisk

    Mendel Leisk MMX GEN III

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    I asked Google AI, and it's saying 2016~2019. It mentions T-SB-0135-19, which just says those model years, no mention of a VIN cut-off.
     
    #44 Mendel Leisk, Aug 12, 2026
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  5. GLCReviews

    GLCReviews New Member

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    Sure, and just like with the revised piston rings in the February 2014 and newer Prius'..it matters what month the car was made. But only us nerds who know, know. The 2019, AFAIK could be the whole model year, or not. Would like to know.
     
    #45 GLCReviews, Aug 12, 2026
  6. Mendel Leisk

    Mendel Leisk MMX GEN III

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    Specific VIN's were mentioned for the 3rd gen piston/ring revision.
     
    #46 Mendel Leisk, Aug 12, 2026
  7. GLCReviews

    GLCReviews New Member

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    Yes and there was also info way back in the archives here with a direct link to a legit TSB that explained what month the production swapped over, so my guess is those VIN #s will coincide with that date. Personal experience, I've seen cars build date 01/14 that burned oil and some 03/14 that didn't. TSB was likely true.
     
    #47 GLCReviews, Aug 12, 2026
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  8. Bill Norton

    Bill Norton Senior Member

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    >So you suspect the head gasket was replaced before this current failure? Curious. There's history...
    I'd have the head professionally surfaced, just to know it's flat, and perfectly clean to mate with the new HG. There is a spec for the ideal surface finish.
    One bit of Gen4 trivia... There's a plastic 'coolant flow deflector' in the aft side of the block, mostly near the #1 side. iirc...(n)
    I don't know if the block and head are different... Can you tell?

    >The engine serial number should be associated with your VIN. No idea how to get to this data.

    > This is great to hear! Thanks for reporting.(y)
     
    #48 Bill Norton, Aug 14, 2026 at 9:15 PM
  9. C Clay

    C Clay Member

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    A plastic coolant flow detector? No way. Anyways, she is done. Very stressful- while the good folks at Gasket Masters have a video, they aren't as good as Nutzaboutbolts video. For instance, he throws on the valve cover and never mentions the spec of the bolts (and I assume it's different than the aluminum third gen). I toggled back and forth between videos and that took me longer. Also- similar to the gen 3, the EGR cooler removal is amazingly even more tricky setting next to the inverter. Somethings I learned about life (and myself) during this experience: Oreilly's has more Toyota parts in stock and cheaper [also validated with Highlander parts] (and they will DoorDash during a "ship to home only" promotion", Walmart delivery is worth it [and they will bring alcohol for when it gets to that point], reduce the steps between car and tools, buy a good tarp and tie downs before it rains (the flow of the rain went directly into the block it seems), account for all tools at all times- still missing a critical 12mm socket (turned out not so critical).

    Attached are some photos that show nothing other than a diary of various issues or stages. I'm sure some will wonder what they are :).

    At the end of the day, I can assure you that the 2019 Prii do in fact, at least according to my experience and about three people on line, need new headgaskets. I sure do appreciate this group and so may others resources! Forgive me for my snark dry humor- but the amount of posts I made where in the first sentence or two I mention the heat exchanger was already bypassed and folks argue I have a heat exchanger issue was pretty funny.

    This is my third HG and my fourth tear down in like 5 months. I don't enjoy it, swear I'll never do it again, but with the expenses of life going up and up - I feel Prii will be in my future for a long time. Cheers all! [​IMG]
     

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    #49 C Clay, Aug 19, 2026 at 9:29 AM
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