Losing coolant but car runs fine

Discussion in 'Gen 4 Prius Technical Discussion' started by andy song, Dec 27, 2025 at 7:45 AM.

  1. andy song

    andy song Junior Member

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    I have been needing to put in about a quart of coolant every 3 days into the bottle

    I can see white smoke from the tail pipe

    But the car drives fine. No misfire. No check engine light

    A friend said it is a head gasket but I don't think it is as i never feel any shaking from the engine.

    Anyone losing coolant from the gen 4 prius?

    Car is a 2021 AWD
     
  2. Bill Norton

    Bill Norton Senior Member

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    I just bought a '19 Gen 4, so I've been doing a bit of research.
    There was a problem with the EGR coolant getting into the exhaust system directly in the Catalytic Converter area.
    I think there was a TSB or recall on this problem.
    You may qualify!
    Good luck!
     
  3. Brian1954

    Brian1954 Senior Member

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    It is not the EGR system but the exhaust heat recovery system (EHRS). Coolant is leaking from the heat exchanger into the exhaust system just in front of the catalytic converter. Very common problem on the Gen 4 Prius. Do a search in this forum and you find a lot of information. This should be covered by the Toyota warranty.

    @andy song , Take the car into your local dealership to get it fixed under warranty.
     
    #3 Brian1954, Dec 27, 2025 at 8:39 AM
    Last edited: Dec 27, 2025 at 9:41 AM
  4. BiomedO1

    BiomedO1 Senior Member

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    That would be covered under the federal emissions warranty 8yrs or 100K miles or you may be able to talk the dealership into replacing it for free, reference the TSB. I don't believe the 2021 model year was covered under that - but it doesn't hurt to ask.
    If they refuse to cover it for free; just by-pass/loop the hose at the heat recovery unit, behind the CAT. There's a few YouTube videos and multiple threads on this forum about this. Search 'exhaust gas heat recovery'

    Hope this helps.....
     
    #4 BiomedO1, Dec 27, 2025 at 9:34 AM
    Last edited: Dec 27, 2025 at 1:30 PM
  5. Mendel Leisk

    Mendel Leisk MMX GEN III

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    Bill did you forget your Ginkgo Biloba this morning? ;)
     
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  6. Bill Norton

    Bill Norton Senior Member

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    No, just new to a Gen4.:rolleyes:
    Isn't there something about EGR being taken post CAT?

    I've had mine for exactly 2 weeks now and loving it!
    Still learning the systems and their names....:whistle:
    It's a '19 ECO with only 235k miles on it. So I got it for a song!
    The Champ!!
    upload_2025-12-27_11-44-41.png


    Next I'm buying a Comma for it. That was the driving force to give up on Gen3's.
    That and head gaskets. Once is enough.....:mad:
    But the quietness and improved fuel economy are added treats !

    I cleaned the battery fan filter, for the first time from the looks of it, but it was easy and satisfying!
    And today the engine oil/filter and transaxle ATF. Mobil 1 all the way! I won't argue about using WS, again...
    I like premium lubes !!:whistle:
    And soon both air filters will arrive.
    I'll test the engine coolant and then, relax and drive the Hay'L out of it. while I wait for the Comma to arrive.
    Are there threads here about setting up the Comma?

    Updating my signature soon.
    How about that for jacking a thread???? o_O
     
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  7. rjparker

    rjparker Tu Humilde Sirviente

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    Leaking coolant into the Exhaust Heat Recirc system at a high rate needs repair or bypass asap. Otherwise you risk a badly overheated engine and then a head gasket.

    Gen4 Exhaust Heat TSB.jpeg
     
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  8. BiomedO1

    BiomedO1 Senior Member

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    thanks @rjparker - I guess my memory isn't that bad from old age.o_O:rolleyes::ROFLMAO::whistle::love:(y)
    I don't believe Wisconsin is a CARB state.