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How much coolant loss is normal?

Discussion in 'Gen 4 Prius Main Forum' started by Prius2016excel, Oct 12, 2022.

  1. Prius2016excel

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    Simple question really. How much coolant loss is normal?

    I had the heat exchanger fault 5 months ago and had it replaced by Toyota. 2016 - complete power loss / breakdown | Page 2 | PriusChat
    Car has been absolutely fine since. I’ve put another 12k miles on it since the repair.

    Obviously with the coolant issues I’ve kept an eye on it and it’s reduced by about 5mm over the last few months. Not much, well within the LOW/HIGH markings, but noticeable. Always checked under the same conditions: completely cold engine, same flat level surface.

    Anything to worry about? I understand it’s a sealed system so in theory should lose nothing but I guess there’s going to be some.





     
  2. bisco

    bisco cookie crumbler

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    In ten years, mine hasn’t changed
     
  3. CR94

    CR94 Senior Member

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    That's a good question.
    It's hard for me to believe there wouldn't be slight normal loss. Otherwise would require that the pressure release cap never vents due to thermal expansion, and that all coolant hoses and gaskets are absolutely impermeable to water vapor.
     
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  4. Georgina Rudkus

    Georgina Rudkus Senior Member

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    Should be none, if the car is in good order and not leaking.
     
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  5. Mendel Leisk

    Mendel Leisk Senior Member

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    Our 2010’s coolant reservoir levels, both engine and inverter, both gradually dropped during the first few years ownership. When they were near low line I topped both up. In the ensuing nearly seven years they haven’t budged.

    question in my mind: with the 4th gen replacement heat recovery units, was there any revision, to avoid a repeat?
     
    #5 Mendel Leisk, Oct 12, 2022
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  6. ChapmanF

    ChapmanF Senior Member

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    I'm more or less with bisco: I can't say "no change for ten years", because I don't go that long without changing the coolant. But in between deliberate changes, it tends to stay right on the line where I filled it without noticeable loss.

    In a degas-bottle system like Gen 3, there is plenty of headspace in the bottle that can be compressed as the fluid expands. It does not rely as much on the pressure cap venting as the older recovery-bottle systems like Gen 2 (where fluid gets expelled through the vent cap and slurped back in on every drive cycle) did.

    On the other hand, it doesn't surprise me in the first week or so after a fluid change if the level changes slightly, with some last bubbles of air finding their way to the degas bottle.
     
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  7. Jburner

    Jburner Member

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    Has the outside temperature changed? The coolant level will change with lower outdoor temps.
     
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  8. douglasjre

    douglasjre Senior Member

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  9. Doug McC

    Doug McC Active Member

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    According to the TSB there was a change in the design (if I remember right).
     
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  10. Mendel Leisk

    Mendel Leisk Senior Member

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  11. Colorado Boo

    Colorado Boo Active Member

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    If it's just a little then I would keep an eye on it but wouldn't worry about it. Any leaks would be noticeable on one of the levels....the left coolant tank, I believe, is for the engine and radiator while the right tank is for the traction engine cooling. Which one looked a little lower?

    If the level does go down more, you can use a flashlight to inspect all around the radiator for anything pinkish in color. Follow the hoses all around looking for signs of anything pink or red. If nothing, you'll have to get underneath, remove the large cover, and inspect all down there paying especially to the heat transfer which is on the muffler.

    Keep us updated!
     
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  12. Kenny94945

    Kenny94945 Active Member

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    I'd agree to "none".
    However, service work 5 months/ 12k mileage ago, just perhaps there were air trapped/ bubbles that settled over time.
    Only recently the coolant level was noticed.
    FWIW
    Prudently I would use some light/ lamps and trace all the coolant lines to rule out a leak.
    Weather temperature could be a valid diagnosis.
    Lastly, no joke, inspect the coolant cap gasket - can evaporate and leave no traces.
    I'd top off, continue to monitor and not worry at this time.
    Good luck.
     
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  13. Kenny94945

    Kenny94945 Active Member

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    I'd agree to "none".
    However, service work 5 months/ 12k mileage ago, just perhaps there were air trapped/ bubbles that settled over time.
    Only recently the coolant level was noticed.
    FWIW
    Prudently I would use some light/ lamps and trace all the coolant lines to rule out a leak.
    Weather temperature could be a valid diagnosis.
    Lastly, no joke, inspect the coolant cap gasket - can evaporate and leave no traces.
    I'd top off, continue to monitor and not worry at this time.
    Good luck.
     
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  14. JGC61

    JGC61 Active Member

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  15. Prius2016excel

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    Yes, and my repair was done with part 17410-37B52. I do find it rather strange though that the TSB from 2019 states that both that part and the original (17410-37B50) have been superseded by 17410-37D40. Having said that there are no known failures of a repaired heat exchanger that I’m aware of and for it to fail in 5m is highly improbable.


    Yes, this could be it. Water contracts of course in cooler temperatures. 6 weeks ago it was high 60s/70f in England, today it was 55f at midday.


    Thanks will do. It’s reduced by bang on 5mm now. Quick visual inspection shows no obvious problem. Hopefully it’s nothing!
     
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  16. Mendel Leisk

    Mendel Leisk Senior Member

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    Maybe said already, could be stray air pockets working out, post install.
     
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  17. Prius2016excel

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    Thought I’d update this approx 10 months on from having the heat exchanger replaced and having added approx 25k miles in that time. Coolant (cold engine) now sitting very close to the low line so there’s been some definite loss somewhere -(it was bang on the high line after being replaced). Car otherwise is absolutely fine at 125k miles.

    EA3C9AF3-BDFE-43AB-890E-93364AAE387C.jpeg
     
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  18. bisco

    bisco cookie crumbler

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    in a thread from today, poster said the car over heated and blew the head gasket some time after the heat exchanger tsb was performed.
    i'm wondering if the fix doesn't always fix it
     
  19. Mendel Leisk

    Mendel Leisk Senior Member

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    Perhaps the replacements are still failure prone? You’d hope not…
     
  20. CR94

    CR94 Senior Member

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    Yeah. I suspect that after the supposed fix, either there was a leak that was overlooked until too late, or else the pump wasn't pumping for some reason. Or possibly the engine was already ruined before the tsb was performed.