2018 Toyota Prius has coolant leak and strange noise

Discussion in 'Gen 4 Prius Care, Maintenance and Troubleshooting' started by Willow.D, Dec 8, 2025 at 1:09 PM.

  1. Willow.D

    Willow.D Junior Member

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    Hello,

    I need help troubleshooting a coolant leak on my 2018 Toyota Prius. Since I bought it used, the coolant has been leaking. It originally leaked into the engine oil due to high pressure, but after removing the reservoir cap O-ring, that issue stopped.


    Now the coolant keeps leaking—possibly from the reservoir or somewhere else. Today, after a long freeway drive, the engine overheated. I added about a gallon of distilled water, but it kept pushing out of the reservoir, and I heard a strange noise that might be coming from the water pump.


    Any advice would be appreciated. Thank you.
     
    #1 Willow.D, Dec 8, 2025 at 1:09 PM
  2. bisco

    bisco cookie crumbler

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    the coolant can leak out of the exhaust gas heat exchanger (known issue) then the engine overheats and the head gasket blows.
    the sloshing is from the coolant in the muffler. there are youtube videos
     
    #2 bisco, Dec 8, 2025 at 2:28 PM
    Willow.D and Mendel Leisk like this.
  3. Willow.D

    Willow.D Junior Member

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    I have a video uploaded on YouTube but I can’t post it since I’m new member. The engine is running good to me. It has around 240k miles on Odometer. Since removing the o-ring reservoir cap. There is no more coolant leak into the engine. I think it must be going somewhere

    When the pressure pushing out the coolant through the reservoir . I can hear a noise, sounds like something broken. Hopefully I can post a link here after sometime, so you can hear the noise. Thanks
     
    #3 Willow.D, Dec 8, 2025 at 2:46 PM
    Last edited by a moderator: Dec 8, 2025 at 7:06 PM
  4. Willow.D

    Willow.D Junior Member

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    It’s over 240k miles. Car is running good, no coolant leaked into the engine oil for now

    I don’t think the engine is running out. Except the coolant leak. Thanks
     
    #4 Willow.D, Dec 8, 2025 at 2:53 PM
    Last edited by a moderator: Dec 8, 2025 at 7:06 PM
  5. Willow.D

    Willow.D Junior Member

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    I have posted a shorted clip on YouTube named “December 7, 2025”. Since I can’t post it here, appreciate if you can do search and watch it.
     
    #5 Willow.D, Dec 8, 2025 at 3:09 PM
  6. Mendel Leisk

    Mendel Leisk MMX GEN III

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    And with the added gallon being water, an additional conundrum: how to restore system to 50% coolant mix. Some thoughts on that in my signature (on a phone turn it landscape to see signatures).
     
    #6 Mendel Leisk, Dec 8, 2025 at 3:59 PM
  7. Willow.D

    Willow.D Junior Member

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    #7 Willow.D, Dec 8, 2025 at 7:19 PM
  8. Brian1954

    Brian1954 Senior Member

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    The engine cooling system was not designed to cool the engine with the o-ring on the reservoir cap removed. It was also not designed to work properly with the reservoir cap removed. It is designed to run at about 14.7 psi of pressure so that the engine coolant has a higher boiling point. The cap is designed to release any excess pressure above the designed 14.7 psi.

    You can believe what you want to, but the fact is the engine needs to be replaced or rebuilt in your car. Why do you think the previous owner got rid of the car?

    How long have you owned the car?

    Have you used a scanner to monitor the engine coolant temperature while the engine is running? That is something very easy for you to do.

    Edit, corrected my sentence, Why do you think the previous owner got rid of the car?
     
    #8 Brian1954, Dec 8, 2025 at 7:44 PM
    Last edited: Dec 8, 2025 at 8:29 PM
  9. Willow.D

    Willow.D Junior Member

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    I’ve owned the car for over a year and drive it daily, though I don’t take many long freeway trips. I’ve been topping off the coolant whenever it gets low and continued driving. Recently, I’ve had to add coolant more often. I check the engine oil frequently and it’s clean with no signs of coolant mixing. I also haven’t noticed any change in engine performance since I bought the car.
    Here is the video i recorded: https://youtube.com/shorts/UwfK-Qt17sI?si=5e_FMYijzX0l53RL
     
    #9 Willow.D, Dec 8, 2025 at 8:09 PM
  10. Brian1954

    Brian1954 Senior Member

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    This is very confusing. It appears that there are now two discussions that are happening in two different threads by the same person using two different usernames on this forum. It appears that users "dv.1000" and "Willow.D" are the same person.

    The link to the other thread is here, https://priuschat.com/index.php?posts/3584251
     
    #10 Brian1954, Dec 8, 2025 at 8:16 PM
  11. Brian1954

    Brian1954 Senior Member

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    How long ago did you remove the o-ring from the reservoir cap?

    Without the o-ring on the car, coolant is just escaping out of the reservoir past the cap. That is the reason why you need to constantly add more coolant.

    IMO, you need to fix the engine or buy a different car.
     
    #11 Brian1954, Dec 8, 2025 at 8:26 PM
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