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
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