Unnerving Engine Noise At Cold Startup

Discussion in 'Gen 3 Prius Main Forum' started by car78412, Jan 9, 2021.

  1. car78412

    car78412 Member

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    I have a 2010 Prius with 110,000 miles. Since COVID-19 began, it hasn’t been used much. After sitting for 5-10 days in a heated garage, cold startups have become quite noisy. It’s a mechanical sound from the engine like the pistons are hitting something or something quite serious. It’s not burning oil and runs quiet after that initial start up. There is no engine light and the car runs fine. If I start it the next day, it runs normal. Can some suggest where I would begin to diagnose?
     
  2. bisco

    bisco cookie crumbler

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    search 'egr circuit' and 'blown head gasket'
     
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  3. ASRDogman

    ASRDogman Senior Member

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    If you didn't have it before sitting, it's probably not the head gasket.
    The hot and cold cycles from day and night could cause condensation inside the cylinders
    and/or intake manifold which would cause it to knock.
    There are several things it could be. Look for the simplest things first.

    You need to drive the car for 30 minutes or so, so any condensasion can be burned off.
    Check the coolant level before you start it. Then check it the next morning after you've
    driven it and it has sat. If it's in the same spot. It's likely your head gasket is fine.

    It is also possible after sitting for 10+ days the fuel pressure has blead down.
    and it will take a few seconds to build up the pressure again. And the system thinks
    it needs more fuel and tries, then it gets too much. It could take several seconds for it
    to equal out. Thus causeing the knocking...

    You have had the eger circuit cleaned, correct? :)
     
    #3 ASRDogman, Jan 9, 2021
    Last edited: Jan 9, 2021
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  4. ChapmanF

    ChapmanF Senior Member

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    My Gen 1 made that sound frequently at startup late in its life, in colder weather especially. Never did find out what it was; sold the car after it encountered an eastbound Dodge Dakota.

    Gen 1 didn't have EGR at all, and I never had any indication, by coolant, oil, or compression, of any problem with the head gasket.

    Sure was an unnerving sound though.
     
  5. car78412

    car78412 Member

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    Thanks for the info. I haven’t checked the egr pipe yet.
     
  6. Mendel Leisk

    Mendel Leisk Sunday driver DIY’r

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  7. Vman455

    Vman455 Active Member

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    It's a cold start knock; search the forum and you'll find it's quite common when the weather is cold and the car sits for several days. (I had it happen for the first time this winter since I'm not driving very often now). Solution: drive it more frequently. Toyota issued a TSB and updated the intake manifold for 2012-2015, but those later cars do it too.

    2013 Prius scary noise at Cold start. | PriusChat
    NEW!!! Service Bulletin for Engine Knocking at Startup T-SB 0012-10 | PriusChat
    Engine Knocking (twice) at Startup - Anyone Else Experience? | PriusChat
     
  8. Mendel Leisk

    Mendel Leisk Sunday driver DIY’r

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    So knocking when cold is a cold start knock? ;)
     
  9. ASRDogman

    ASRDogman Senior Member

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    Knock Knock? Who's There? :whistle:
     
  10. Stangar

    Stangar Active Member

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    ALWAYS let the engine run until it shuts itself off. A good example is when you are moving the car out of the garage and parking on your driveway. Be sure to let it shut down the engine prior to you turning it off. Otherwise, you will get this nasty knocking noise at the next start.

    (You will eventually need to clean the intake manifold, EGR cooler and add a oil catch can for engine longevity)
     
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  11. Mendel Leisk

    Mendel Leisk Sunday driver DIY’r

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    True, but like dealing with a problem child.
     
  12. High Mileage

    High Mileage Active Member

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  13. Mendel Leisk

    Mendel Leisk Sunday driver DIY’r

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    I’ve become adept at shuffling the car around the driveway in that 15 second (max!) grace period, before the engine kicks in. And, a fringe benefit of a block heater: with 1~2 hour plug in, it can spoof the car into giving you EV mode. :)
     
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  14. Yaesu

    Yaesu Junior Member

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    I have read that the knocking is due to condensation in the intake manifold. I occasionally notice it, including on the first startup after being stored for six months in a non-heater garage. I asked the Toyota dealer about it and they said that "they" would have to observe it before they could do anything about it. Since it happens so rarely, I chose to do nothing about it. I do not turn the engine off before it has warmed up sufficiently to turn itself off.
     
  15. Grit

    Grit Senior Member

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    If I knocks during the summer, will it be classified as hot start knock?
     
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  16. Grit

    Grit Senior Member

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    before hitting the panic button, drive it everyday around town til operating temp is reached then that should take care of condensation inside the cylinder pistons. If it doesn’t, get a leak down test since it’s a 2010 so you don’t end up throwing money/parts with a blown head gasket
     
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  17. Vman455

    Vman455 Active Member

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    Sure, if it's 190 degrees outside.
     
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