Underlying Cause of Head Gasket Failures?

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by rjparker, Jul 29, 2021.

  1. rjparker

    rjparker Senior Member

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    We seem to be in full crisis mode on gen3 head gasket failures with some hg repairs failing as well. I am sure many failures end up at auto auctions and then are flipped with block sealers based on the number of buyers having problems.

    The gen3 engines are known oil burners, egr cloggers and depend on knock sensors since they have 13 to 1 compression but use regular gas. At the same time most run fine for well over 125k-200k miles before the rattles began. It is unlikely gasket materials or clearances are the root cause when they last that long.

    Could detonation knocking caused by carbon buildup, lean fuel mixtures, failing knock sensors, egr clogging and or poor octane be likely suspects when overheating is not the issue?

    The gen4 1.8 engineering seems to offer clues. Toyota redesigned upper cylinder cooling through use of steel and foam spacers, increased cylinder turbulence, changed the intake to improve egr flow, revised the egr cooler size and location, all of which can reduce knocking which blows head gaskets.

    So do we just trade gen3s at 150k, always run premium fuel (one trusted mechanic's advice) or build up an engine repair fund?
     
    #1 rjparker, Jul 29, 2021
    Last edited: Jul 29, 2021
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  2. Grit

    Grit Senior Member

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    impossible, the priuschat moral police would have stopped & jailed the perps even before gasket sealant is poured in! Your giving permission for people exercise such practice.
     
    #2 Grit, Jul 29, 2021
    Last edited: Jul 30, 2021
  3. Mendel Leisk

    Mendel Leisk Sand Pounder

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    Cleaned the intake manifold, EGR circuit, installed oil catch can(s), just past 70K kms. Will likely revisit the EGR with the spark plug change, at 12 years, and likely around 100K kms.

    Not burning ANY oil so far, doing 6 months oil changes, at undisclosed kms (don't want to be hauled off...). At oil changes I put in 4.2 liters, and it's about 1/8" below top mark on dipstick. When the next oil change rolls around, hasn't budged.

    AD910AA5-022A-4274-8944-D662FECAF1EC.jpeg
     
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  4. fuzzy1

    fuzzy1 Senior Member

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    That is the expansion ratio. No normal Prius has anywhere near that much compression.
     
  5. rjparker

    rjparker Senior Member

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    A Prius has control over its compression ratio and mimics a variable displacement engine through valve timing. 6.5:1 compression stroke and a 13:1 power stroke.

    As we have discussed before, the variable valve timing provides variable compression ratios. The ratio on the power stroke is at least 13/1 no matter what you call it. Knocking can and does happen. Add carbon and knocking increases.

    The point of the thread was "what is going on with gen3 head gaskets". Knocking is a known factor in head gasket failures. Many other factors are likely including thermal cycling which may allow failures, another factor which Toyota worked on in gen4 with the foam and steel spacers.

    Nevertheless I agree with Jzchen's earlier viewpoint on knocking:
     
  6. ChapmanF

    ChapmanF Senior Member

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    What is happening on the power stroke is that the charge is expanding. As fuzzy1 correctly pointed out, the ratio by which it expands is known as the expansion ratio.

    The charge is only being compressed on the compression stroke, and the valve timing makes that ratio less than 13:1. That's what makes the engine an Atkinson-cycle engine: the fact that its expansion ratio exceeds its compression ratio.

    The engine does indeed have a knock sensor, like pretty much any other modern engine, and does have to be able to react (such as with ignition timing) to keep itself out of knocking conditions, like pretty much any other modern engine. None of that is because of "13 to 1 compression", which it doesn't have.
     
  7. ETC(SS)

    ETC(SS) The OTHER One Percenter.....

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    If you replace the head gasket without addressing the root cause of the head gasket failure, it's "probably" going to fail again, don't you think?

    It's easy to blame the OEM for building a car that won't last much more than 120,000 miles with a 10,000mile OCI, and modern drivers that pretty much expect to maintain a closed-hood maintenance philosophy.

    There ARE some design issues with the G3, as there are with any car.
    IMHO the EGR circuit is prone to getting plugged up, the oil sump is about a quart too small, and the OCI is too long.
    The pistons are well documented as well.

    You CAN inform yourself of some of the design issues with the G3 and mitigate some of the those by doing some of the things we talk about in this forum...like oil catch cans, reduced OCI, and oil level checks at least as often as required by the OEM.

    Most people don't.
    They sell the car at some point and owner #2 gets an unhealthy middle aged car with almost a 100 percent blockage of the left anterior descending (LAD) artery.....commonly referred to as....a widowmaker.

    Next thing you know....the G3 Prius get the same reputation for quality and longevity as Fiat. :ROFLMAO:

    Remember that the cars are built in Japan, and they generally do not amass the same number of miles that their US spec card do, AND YET the Japanese also have used Priuses quite successfully as fleet vehicles (taxis) as have companies in the US.
    Just a guess here, but fleet operators (even MINE!) have different maintenance modalities than private (gas and go) drivers.

    THIS is why.....ACTUAL mileage WILL vary. ;)
     
  8. bisco

    bisco cookie crumbler

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    do we have a conclusion yet? i've got almost 25,000 miles on my engine, and i'm getting nervous...
     
  9. rjparker

    rjparker Senior Member

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    I am doing my best to wake up the community. Answers like it is "normal" are pretty sad.
     
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  10. Grit

    Grit Senior Member

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    i’m nervous about the hv bat not getting charger cycles if you got 25,000 miles only on the car
     
  11. ETC(SS)

    ETC(SS) The OTHER One Percenter.....

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    He has a pip.
     
  12. bisco

    bisco cookie crumbler

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    i am a pip

    if only toyota would disclose the truth, i'm sure they know the facts
     
  13. ETC(SS)

    ETC(SS) The OTHER One Percenter.....

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    Concur.
     
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  14. Mendel Leisk

    Mendel Leisk Sand Pounder

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    The dots I connect:

    1. Cylinder 1 is where predominance of 3rd gen gasket failures start.

    2. The intake manifold’s EGR capillary passage for cylinder 1 always seems to clog first.
     
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  15. Kenny94945

    Kenny94945 Active Member

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    Um, interesting question and discussion.
    I venture to say in many cars head gasket failure is attributed to water jacket location or high compression (or an over heat condition).
    Coolant flushes can be a good maintenance item to reduce risk.

    I don't recall anyone every mentioning re-torqueing the head bolts.
    A common initial critical fastener check on motorcycles as a general example.

    Predicting failure can be futile.
    So, I could suggest a head bolt re-torque at an initial 10K service and a follow up at 50K.
    But, I have not done this nor am I too concerned.
    FWIW

    Have fun.
     
  16. jdenenberg

    jdenenberg EE Professor

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    Since you have a GEN 4 Prius and not a GEN 3, that is a consensus view.

    JeffD
     
  17. mr_guy_mann

    mr_guy_mann Active Member

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    Well, the service procedure for cylinder head installation shows a "torque + angle + angle" sequence on the head bolts. So they are torque to yield (or torque to angle).

    What would you have the head bolts "re-torqued" to?

    Posted via the PriusChat mobile app.
     
  18. Mendel Leisk

    Mendel Leisk Sand Pounder

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    His 2016 Prius v would have a gen 3 engine, identical to 2015 Prius I think. That said, I wouldn't touch head bolts.
     
  19. fuzzy1

    fuzzy1 Senior Member

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    I had understood that only the 2016 Liftback was a Gen4. The 2016 'v' and 'c' were still Gen3s.
     
  20. wheezyglider

    wheezyglider Active Member

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