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2015 Prius C 99k: engine rattle on start and acceleration first 15 min

Discussion in 'Prius c Care, Maintenance and Troubleshooting' started by manydelays, Feb 13, 2023.

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  1. manydelays

    manydelays New Member

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    Location:
    Los Angeles
    Vehicle:
    2015 Prius c
    Model:
    Two
    Hi!

    My 2015 Prius C has a worrisome rattle/flapping sound when starting, idling, and accelerating for the first 10-15 or so minutes. It is definitely coming from the engine and is audible inside the vehicle as well as outside.

    I did some research and came up with a few potential causes:

    -spark plugs (that would be great)
    -EGR Valve / System clog
    -failed head gasket

    When I took the car into the shop upon purchase, the shop was unable to replicate the sound - probably because I had to drive a while to get there. When I took to the dealership, they informed me of a timing seal leak/seepage that would require a $2k+ repair. Although, I am not sure this is related to the rattle.

    I have not noticed any coolant leakage, so I am fairly sure it is not a failed head gasket.

    Could anyone shine some light on the EGR valve/system possibility?
    I have great fuel economy, no smells, no smoke, no nada except for this rattle.

    To describe the sound even better, it almost sounds like a flapping? I feel it is definitely related to the passage of air through some component and possibly temperature is a variable (due to the fact it fades when the car has been running for some time)

    Thank y'all for your time and consideration.
     
    #1 manydelays, Feb 13, 2023
  2. manydelays

    manydelays New Member

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    Two
    Another Prius C driver listed this sound as a "mystery ticking" which also increased during acceleration. I do believe we are referring to the same phenomenon.
     
    #2 manydelays, Feb 13, 2023
  3. bisco

    bisco cookie crumbler

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    the timing seal is a bogus way to make the dealer big bucks. can you leave it overnight so the mech can drive it cold?
    egr is probably worth cleaning, although i don't think it has the same issues as the lift back.

    it's early for plugs, but easy to check. a leak down test can confirm hg go/no go

    how is the oil level? is it the correct weight?
     
    #3 bisco, Feb 13, 2023
    Leadfoot J. McCoalroller likes this.
  4. bisco

    bisco cookie crumbler

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    are you saying you just bought the car in this condition?
     
    #4 bisco, Feb 13, 2023
  5. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    Ignore the timing cover seep. That's all it is. A drop or two of oil a month.

    It's early for plugs, but not that early. Lots of documentation of worn plugs causing ignition misfires, and even more about misfires being particularly noisy in the Prius engine- all posted on this site.

    So given the good running, good MPG and other info I'd say install new plugs and maybe think about changing gas stations.
     
    #5 Leadfoot J. McCoalroller, Feb 13, 2023
    bisco likes this.
  6. nicoj36

    nicoj36 Active Member

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    Try BG moa for hybrids. It's an oil additive that eliminates loud ticks and quiets engines down.
     
    #6 nicoj36, Feb 13, 2023
  7. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    To add to earlier:

    I have not driven my own Prius in Los Angeles, but I did live there years ago.

    I had a Ford truck that really did not run properly when I used grocery store or warehouse club gasoline, but when I filled up at an oil company station like Shell or Mobil or 76 it ran great.

    Just tossing that out there.
     
    #7 Leadfoot J. McCoalroller, Feb 13, 2023
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