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 at 4:07 PM.

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  1. C Clay

    C Clay Member

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    I searched back through posts for some good how to posts and find nothing. I see a lot of "you probably need a new head gasket", but none of the rich content like is available for the Gen3. I've done 2 head gasket jobs this year, so I'm familiar with the task. Unfortunately, my 2019 is looking like she's needing this done and I'm just wanting to read/view some experiences as a sanity check.
     
    #1 C Clay, Jul 26, 2026 at 4:07 PM
  2. Mendel Leisk

    Mendel Leisk MMX GEN III

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    These were 4th gen's?

    Due to some symptoms?
     
    #2 Mendel Leisk, Jul 26, 2026 at 4:10 PM
  3. C Clay

    C Clay Member

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    I’ve done a 2011 and a 2014.

    My symptoms on my 2019:
    -Billowing white smoke upon starting in maintenance mode yesterday morning
    -using about 2-3 of coolant each morning (refilling from the loss each day)
    -snot mix on the inside of the oil
    filler cap (I already cleaned it last week)
    -rule out head exchanger, I bypassed that almost immediately after buying it.

    Sure seems head gaskety. Not sure how or why it happened. It did happen after my first “big trip”- 600 miles up to Baltimore, back through the WV mountains. I did feel like sometimes I was going straight up a steep incline for 10 miles lol- maybe I pushed her too hard.

    I just bought it. Had 205000 miles on it.
     

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    #3 C Clay, Jul 27, 2026 at 9:38 AM
  4. Mendel Leisk

    Mendel Leisk MMX GEN III

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    Was the exhaust heat exchanger leaking? Maybe previous owner had neglected coolant top-up, let the engine run dry a time or two, led to head gasket failure. That’s been reported here before.
     
    #4 Mendel Leisk, Jul 27, 2026 at 9:53 AM
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  5. ETC(SS)

    ETC(SS) The OTHER One Percenter.....

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    +1.
    I was tapping this while he was typing that......

    First, make sure you really have a failing head gasket!
    The G4 has a common manufacturer defect in the exhaust heat exchanger that can cosplay as a blown head gasket.
    Cracks in the plumbing allow coolant to leak directly into the exhaust system rather than onto the ground by causing mysterious coolant loss and white exhaust smoke without the Prius Death Rattle caused by coolant getting into the cylinder bore.
    Toyota released a technical service bulletin (TSB T-SB-0135-19)and I suspect that there will be a video as the G4s age a little bit more and suffer from being "dealer maintained."
    G4's probably overheat more from resulting coolant loss because you do NOT have the Prius Death Rattle, and this WILL cause head gaskets to fail from heads warping rather than blocks being hydro-locked.

    The oldest G4s are coming up on 10 years and truthfully speaking they have been much more reliable than the G3s.
     
    #5 ETC(SS), Jul 27, 2026 at 10:00 AM
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  6. Mendel Leisk

    Mendel Leisk MMX GEN III

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    One thing, it’s early years of gen 4 that we’re having the exhaust heat recovery (EHR) system leaks. My memory’s flakey, but it might have been resolved by model year 2019. Not sure though.
     
    #6 Mendel Leisk, Jul 27, 2026 at 10:06 AM
  7. C Clay

    C Clay Member

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    Even after I bypassed the heat exchanger (and I did it under the car), you are stating there is still a way for the coolant to be leaking into the exhaust? IMG_4512.jpg
     
    #7 C Clay, Jul 27, 2026 at 10:13 AM
  8. C Clay

    C Clay Member

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    I’m sure it is unrelated, but listen to the car in maintenance mode. Probably best around 35 seconds. There is something clanging in her that I am disturbed about.

    When you try and diagnose issues- I think of everything I know about the cars history and everything since I’ve had it. Drives fine, 52-54 mpg.

    And then there was that day I jacked it up under the wrong jack point and bent the subframe a little, shooting the radiator up slightly so that the hood forces open and I wouldn’t shut. I pulled that all back down. I call that “stupid tax” for being in a hurry on my first oil change.

    The car doesn’t appear to have any issue related to that event- no coolant loss that I ever saw from say a damaged radiator.
     
    #8 C Clay, Jul 27, 2026 at 11:17 AM
  9. Mendel Leisk

    Mendel Leisk MMX GEN III

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    Not sure he's saying that.

    Sequence that does make sense, assuming the EHR system did have a leak:

    1. EHR system commences leaking.
    2. Owner doesn't notice for some time, belatedly tops up coolant, but by then engine's run dry a time or two, overheated, and head gasket commences to leak coolant into combustion chambers.
    3. EHR system is bypassed, but head gasket continues to leak.

    Regarding your original question, I think 4th gen head gasket replacement would be VERY similar to 3rd gen, the engine being "mostly" identical.

    The imgur video sounds "somewhat" too noisy. Is it worse on cold starts? That tends to be when significant coolant accumulates, causing very nasty sounding bangs.

    Just technical: is there an arched/ribbed face of the wheel chock against the ground, and flat face against the tire? If so, think it should be flipped:

    upload_2026-7-27_9-8-49.png
     
    #9 Mendel Leisk, Jul 27, 2026 at 11:56 AM
    Last edited: Jul 27, 2026 at 12:08 PM
  10. BiomedO1

    BiomedO1 Senior Member

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    And if you don't get hot coolant going pass your temperature sensor ( too low) your dummy lamp isn't going to light up....:(
    You could've crushed some cooling coils, that isn't leaking, but caused enough restriction to reduce cooling capacity. Newer car designs are very stingy on parts requirements and there isn't much excess capacity to spare on folly.:notworthy::cry:
     
    #10 BiomedO1, Jul 27, 2026 at 1:16 PM
  11. Bill Norton

    Bill Norton Senior Member

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    I'm curious why you bypassed the EHR system. I thought it was a known issue and was redesigned by '19.
    I don't think that oil cap looks that bad. It's probably not after you did your big road trip. And on Gen3's the oil rarely gets into the oil. It just seeps into the #1 or 2 cylinders after shut down. This I know, a few times.....:(

    Brother, I just found this thread and I'm following it. Good Luck. I'm sure you can handle this head gasket change.
    Does Felpro offer a Gen4 version?


    I bought a '19 Eco in Dec, '25 with 232k miles.
    I think a courier had owned it. And I use it commercially also and I'm now at 280k miles!

    It runs great, uses very little oil between 5-7k mi oil changes. Mobil 1 all the way!
    I may do an oil analysis test on it because it looks cleanish.
    What's with the 25k mile M1 version? I may be the perfect user for that crazy figure.

    All I did to mine soon after I got home was change the transaxle fluid to Redline D6.
    The ATF that came out was fine looking, so I'm pretty sure someone gave it a change at some point.
    And I cleaned the battery pack fan filter, It seriously needed it.
    I know I should change the engine and inverter coolants... It's a bigger job....
     
    #11 Bill Norton, Jul 27, 2026 at 1:21 PM
  12. C Clay

    C Clay Member

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    On assertion #2- I lost less coolant to the heat exchanger issue that I am losing now.

    The wheel chock is facing correctly
     
    #12 C Clay, Jul 27, 2026 at 1:22 PM
  13. Bill Norton

    Bill Norton Senior Member

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    Sorry for your problem.
    But to me, This is good news!!!:)
     
    #13 Bill Norton, Jul 27, 2026 at 1:24 PM
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  14. C Clay

    C Clay Member

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    It was pretty clear it was the heat exchanger as I understand it. You could smell it while driving actually. The coolant was literally coming out of the exhaust.

    And I did reach out to Toyota, and they wanted no part of replacing it for free with its 205000 miles.

    Interesting, this also was a fleet vehicle of some kind. The maintenance was always done at Toyota or a chain tire place in the area (Nashville- where I bought it, but I live in Kentucky.). The engine is so clean you can eat off of it, and even all the undercarriage parts/plastics are all there. There’s some relationship to the car and the Toyota dealership that I never figured out. Either it was used as a delivery vehicle or maybe a loaner. One year, if I read correctly- it had like 60k miles put on it.
     
    #14 C Clay, Jul 27, 2026 at 1:28 PM
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