Loud bang and the rattle highway speed

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by 2manycars, Mar 7, 2021.

  1. 2manycars

    2manycars New Member

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    New to the Prius world, but I know good noises from bad. Driving at highway speed and from the engine compartment came a very loud bang, kind of like a rod breaking and a few seconds of rattle, rattle, rattle.

    I expected to have lights going off on the dash and an oil slick behind me...nothing. The engine was not running, however the battery kept changing and I wasn't far from home. After shutting it off, it would not "start" and flashed, shift to park.

    The next morning it started and ran ok. Day 2 at 45 mph, a different loud noise like grinding gears of a bad shift with a manual transmission. No other issues the rest of the drive.

    What is about to fail?
     
  2. dbstoo

    dbstoo Active Member

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    You want to take it to a mechanic. Driving it when it's making loud noises is a surefire way to throw a rod, bend valve stems, etc.

    Is this the same car that you mentioned in your other thread? The one that threw a code?
     
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  3. bisco

    bisco cookie crumbler

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    how are the oil and coolant levels?
     
  4. 2manycars

    2manycars New Member

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    Yes, same car. Used K & W block sealant, ran in maintenance mode. Flushed the entire engine coolant including backwash of the heater core. No longer uses any fluid.
     
  5. 2manycars

    2manycars New Member

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    Just changed out both, prior to this.
     
  6. Protec

    Protec New Member

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    Not really enough to go on to make an informed diagnosis I’m afraid.
    Does it make the noise freewheeling?
    Any different noised decelerating?
    Braking?
    Pick the car up, spin each wheel up by hand?
    List is not exhaustive but I’d do this sooner than leaving it imvho
     
  7. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    Right, but how are the levels now?
     
  8. 2manycars

    2manycars New Member

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    All fluid levels are fine and holding. No coolant use and the oil is clean and not milky. Due to earlier code 261B, I installed a new water pump, no apparent issues with the one I took out of it, but not a Toyota one and installed a new thermostat. Backflushed the heater core, now have heat. Seems to be lacking in power, but this is the only 3rd Gen I have driven. In power mode, it takes right off. I am reluctant to drive it far or much. If it had hydrolock or long-term prior to me coolant leaking into a cylinder, could I be experiencing symptoms to do with a bent rod?
     
  9. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    A bent rod will primarily manifest as reduced compression in the associated cylinder which leads right into a rougher run from the weaker combustion and reduced overall power. You can detect it with a compression test. You can directly measure it on the car, with the plugs out by comparing TDC of the four pistons with a long wire probe indexed crossing a reference level set up on the valve cover.

    Usually whatever bent the rod also damaged the bearing on the big end of it- it's just that much stress! So that bearing burns before long, often with souvenir ejecta.

    I don't know what caused the noises on your car- near-hydrolock starts? Classic backfire or exhaust issue? Broken parking pawl getting chewed up in the gearbox? I'm just not close enough to do better than spitballing, sorry.
     
  10. ETC(SS)

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

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    Sounds like you need to down the car for maintenance.
    Used it for *what?* exactly.
    history?
    miles?
    previous problems?

    If you're on head-gasket 2.0:
    Did you repair the underlying problem that led to the original failure?
    Was it repaired "correctly?"

    Bent connecting rod symptoms do not "come and go."
    As mentioned above, the engine usually fails dramatically if operated in this condition.
    The good news is that if this is the case you're going to be in the market for a short block pretty soon anyway.
    Other than getting the car back in the barn, replacing the bottom end is no more difficult (if not less messy) than it would have been before it failed.
     
  11. Mendel Leisk

    Mendel Leisk Sunday driver DIY’r

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  12. ETC(SS)

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

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    Oh....I see.
    Well....it doesn't really matter.

    Sounds like that engine is going to be coming out of the car pretty soon either way.
     
  13. 2manycars

    2manycars New Member

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    Thanks for all the details. Question, how do you crank the engine? Do you have to do Maintenance Mode for each cylinder?
     
  14. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    For a TDC height test? You'd crank the engine by hand for that. You'd want to rock the crank back and forth near TDC to make certain you were really there.

    For a compression test there is a maintenance mode procedure to standardize the results.
     
  15. 2manycars

    2manycars New Member

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    You unfortunately are thinking what I am.
     
  16. 2manycars

    2manycars New Member

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    The service center used a test that checks for exhaust gases at the radiator. Failed within 30 seconds.
     
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  17. ASRDogman

    ASRDogman Senior Member

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    ????????? How in the world can you check for exhaust gasses at the radiator???
    The exhaust manifold is behind the engine. Not even close to the radiator.

     
  18. ChapmanF

    ChapmanF Senior Member

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    The exhaust gases begin life in the cylinder. There's nothing there but a head gasket to keep them out of the coolant passages.
     
  19. Protec

    Protec New Member

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    To check the coolant for “Gases”.
    Use of a 4 or 5 gas exhaust analyser sniffing the vapour/gas is to check for the presence of hydrocarbons. This gives an indication the the cylinder head gasket/hairline crack in the head or block (basically, leakage of combustible gases etc into the coolant)
     
  20. ASRDogman

    ASRDogman Senior Member

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    ??????
    Do you mean "IN" the radiator??? Because outside the radiator does nothing, unless it's leaking.
    Or the exhasust is leaking and your driving backward, or the wind is blowing under the car and up
    over and around the engine.

     
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