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Sudden Coolant loss—I don't think it's the head gasket

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by CloudJumper, Dec 4, 2022.

  1. Xterra72

    Xterra72 Senior Member

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    Engine Coolant water pump is my guess. Same problem I had maybe about a year ago now.
     
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  2. Mendel Leisk

    Mendel Leisk Senior Member

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    You'll see pink crusties if it's leaking at the pump.
     
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  3. CloudJumper

    CloudJumper Junior Member

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    It's not leaking at the pump itself. there is absolutely no sign of leakage anywhere on or by the pump.

    Thank you for confirming my suspicion. Did you ever figure out where exactly the coolant was going? Such as a leak by the water pump itself, or into the combustion chamber or oil (none of which I have signs of) or somewhere else?
     
  4. Brian1954

    Brian1954 Active Member

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    Here is my theory:
    The OP has a water pump impeller that is occasionally seizing (binding) OR the thermostat is not opening correctly and the reduced coolant flow causes the engine to overheat and the dash light to come on. When the engine overheats, the pressure in the coolant system increases to the point that coolant is forced past the screwed on lid on top of the plastic coolant tank and it comes out the little overflow tube that is just below the lid facing the back side of the tank. I just took a look at my car and the overflow tube has a small rubber cap that I assume is there to keep dirt from entering the tube. So this is why the coolant is disappearing from the Op's car.

    Here is a picture of my coolant tank showing the black rubber cap on the overflow tube.

    2011 Prius coolant tank.jpg

    @CloudJumper , Take a look around your coolant tank and see if there is any dried pink residue or evidence of coolant overflow.
     

    Attached Files:

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  5. Brian1954

    Brian1954 Active Member

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    I am a novice in using TechStream and Torque Pro, so I am not much help. Maybe someone else with more experience is willing to help you. I know "just" enough to get myself into trouble while working on my car.

    Can you please give us some history on your car. Are you the original owner? Has the engine coolant, water pump, thermostat ever been replaced?
     
  6. CloudJumper

    CloudJumper Junior Member

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    While I haven't noticed a single speck of pink anywhere near the coolant resivior or the water pump (I feel like it'd be pretty noticalbe after two occurances), this is useful infomration, I will take a closer look today. Thank you for your input.
     
  7. CloudJumper

    CloudJumper Junior Member

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    I've owned the car since 2018 at 100,000 miles. As far as I know, the water pump and thermostat are original, however I have had the coolant flushed and replaced three times during my ownership of just over 4 years / 100,000 miles. Oil changes every 5K miles, most maininance is done by Toyota themselves (I know, I know, stealerships, but tha's why I'm doing my reserch here first). ERG System has been cleaned twice since ownership.
     
  8. Xterra72

    Xterra72 Senior Member

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    In my case, coolant was coming out of the engine coolant reservoir that shows max/ min levels. At first I thought I had a bad cap.

    Told my mechanic and he just topped it off. He said next time it happens, to take it to his shop right away so he can plug it in for diagnostics.

    happened again and I was able to take it to him as instructed. His OBDII computer readings read a bad engine coolant water pump.

    Went to the dealer and replaced it, along with the thermostat for good measures.
     
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  9. Mendel Leisk

    Mendel Leisk Senior Member

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    Just for giggles, boroscope the cylinders with the cooling system pressurized, look for coolant "tears"? I know, but it's third gen...
     
  10. CloudJumper

    CloudJumper Junior Member

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    This sounds exactly like what I'm experiencing. Thank you so much! I don't suppose you remember a ballpark figure of how much they quote you for that service?

    Posted via the PriusChat mobile app.
     
  11. CloudJumper

    CloudJumper Junior Member

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    Unfortunately, I do not have a boroscope on hand. Though I am quite curious to see that.

    Posted via the PriusChat mobile app.
     
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  12. Brian1954

    Brian1954 Active Member

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    I am impressed with the number of coolant replacements that you had done. Sounds like you take very good care of your car.

    When the water pump impeller binds up and runs slower then required, you will get a P261B trouble code. I am guessing that your water pump is not to the point of setting this code but I would advise you to get it replaced ASAP. I would also get the thermostat replaced at the same time, because it is good insurance even if it is not needed. It does not cost very much more.

    The engine over temperature dash light comes on at a fairly high temperature. I do not remember at what temperature, but you can search the Gen 3 forum. In my opinion, it should have been set for a lower temperature.

    I believe the majority of head gasket failures on a Gen 3 are caused by the engine overheating because of water pump failures. I have a P10 display unit plugged into the OBDII port so that I can watch my water temperature and voltage level. I never liked that there was no water temperature gauge included in the instrument panel.
     
    #32 Brian1954, Dec 6, 2022
    Last edited: Dec 6, 2022
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  13. Mendel Leisk

    Mendel Leisk Senior Member

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    Same here.
     
  14. ChapmanF

    ChapmanF Senior Member

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    Because of the degas-bottle cooling system style, there is quite a bit of headspace in the coolant bottle. Even if the coolant ever gets hot enough to exceed the 108 kPa relief point of the cap, there's a bunch of air up there that would be first to escape, before it comes to any coolant escaping. (The air will carry a bit of vapor, of course.)

    There are two temperature sensors that can trigger the red-thermometer light. I tested one and found the light to come on at 120 ℃. I assume it's the same for the other one, but I haven't tested that.

    If any of the water pump trouble codes are set, the ECM will silently, without warning, shut down the engine if it reaches 105 ℃.
     
  15. CloudJumper

    CloudJumper Junior Member

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    Coolant changes every 30-40K miles. I want to pull every last mile out of this car possible. 200,000 miles and these are my first ever mishaps (aside from that one time that the mechanic royally messed up a simple service . . . Hence why I only go to Toyta now ). I'll be sure to replace the pump and thermostat asap to stay on top of that. Thank you!

    Posted via the PriusChat mobile app.
     
  16. Xterra72

    Xterra72 Senior Member

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    I could not find the original invoice but since it’s the stealership, I remember the cost at $1k +\- , for parts & labor.

    Definitely wasn’t cheap but it was well worth it, if done right. I replaced mine at about 175k miles on August 2020. The car is closing in on 220k miles and still going strong.
     
  17. CloudJumper

    CloudJumper Junior Member

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    $1k huh? The removal and installation process doesn't look very difficult based on YouTube videos, and I know the part is roughly $250 from my local dealership. I figured stealership prices would be closer to $500 for parts and labor, before factoring in the price of the thermostat.

    Posted via the PriusChat mobile app.
     
  18. Xterra72

    Xterra72 Senior Member

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    I’m in California. Bay Area. Everything is expensive in my location. It was for sure over $750.
     
  19. CloudJumper

    CloudJumper Junior Member

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    Ah, that is a very good point. Hopefully Minnesota will be more manageable. Thanks again for all your input! It has been very helpful.

    Posted via the PriusChat mobile app.
     
  20. jzchen

    jzchen Newbie!

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    Time out… Now I’m ultimately confused. (Please don’t take this personally I just got my concept of hotter plug corrected). So we are concerned that the EGR plugged causes the engine to run hotter (please correct me if I’m wrong, but now the “hotter plug” seems to contradict that concern?


    iPhone ?