What is the chief cause of head gasket failure on the gen 3

Discussion in 'Gen 3 Prius Technical Discussion' started by Jayw13702, Dec 1, 2017.

  1. howardc64

    howardc64 Member

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    Does anyone think thinner 0W-20 oil contributes to this? Thinner means easier to escape with blowby even with improved engine tolerances.

    Of course having oily blowby filtered out to keep intake clean is good practice. Lots of engines can do this without a catch can. Is gen3 Prius's blowby oil trapping mechanism particularly bad?
     
  2. Mendel Leisk

    Mendel Leisk Sidewalk Supervisor

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    Look through the throttle and you'll see a pool at the bottom of the intake manifold, and who knows how much just passes through.
     
  3. Prodigyplace

    Prodigyplace Senior Member

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    Didn't somebody have a theory that it was the position of the PCV valve or EGR ? There were changes in EGR for Gen 4 so we wonder if that has helped with the issue. It is too early to tell.
    An oil catch can, regularly emptied, seems to help a lot with the issue.
     
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  4. howardc64

    howardc64 Member

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    Yeah seen that in my prior TB cleaning effort which suggest a fairly poor blowby oil filtering design.

    Every design I've seen before (a couple of turbo engines which has really complex PCV designs due to losing intake vacuum when boosting) uses baffles to concentrate the oil from the blowby vapor and gravity drip+drain it back to the block/pan. Haven't pulled IM yet on this engine but I think there is a hose that goes to the block which would be the filtered oil drain return. If this isn't located at the lowest spot, then can't remove all the filtered oil, hence, catch can is the only remaining solution.
     
    #44 howardc64, Mar 21, 2019
    Last edited: Mar 21, 2019
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  5. Mendel Leisk

    Mendel Leisk Sidewalk Supervisor

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    There is a bit of a labyrinth in the engine block, right where PCV valve screws on. It's behind a bolted on plate, maybe 6" square. Drains a little back. Not really effective though.
     
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  6. CR94

    CR94 Senior Member

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    If it's "not really effective," how can normal oil consumption (i.e., before becoming a heavy drinker) be so extremely low overall? So far, mine seems to manage better than 30,000 km/liter (by extrapolation, NOT direct test!).
     
  7. Mendel Leisk

    Mendel Leisk Sidewalk Supervisor

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    I guess from what accumulates just below the throttle body, and/or in an oil catch can.
     
  8. MikeNinMass

    MikeNinMass Junior Member

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    Specualtion: Excessive blow-by can force more oil out the PCV valve. It seems that the updated piston and rings in 2014/2015 might have been to help with blow-by. More speculation, by having more oil fed back if not caught by a catch can, there's more carbon buildup in the combustion chamber, which might prevent the rings from sealing properly, further increasing the blow-by. The more oil you suck into the intake to be burned, the more oil consumption you will have. If you haven't reached stage 2 blow-by, then maybe it's only a little oil burn, slowly building up carbon as the miles go on, then when you hit the right carbon level so the rings don't seal, the heavy consumption starts.
     
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  9. jack black

    jack black Member

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    how about this possibility. prolonged driving at the HSI settings just over the mid point to the right when ICE is in low RPM/high load regimen (about 2000RPM). when i do that, usually cruising about 50MPH, the ICE clearly works hard and you can feel some vibrations, that otherwise go away when one goes to the right end of ECO zone (about 3000RPM). maybe that stresses the HG, especially when the EGR cooler is not pristine.
     
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