2007 Prius Tapping - timing chain or rod knock? (how to test?)

Discussion in 'Gen 2 Prius Technical Discussion' started by JoeVR, Aug 19, 2025 at 1:59 PM.

  1. JoeVR

    JoeVR Junior Member

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    Hi all,

    I have a 2007 Prius that just rolled over 250K last week. It's been a great car, and I have maintained it regularly. I change the oil every 5k miles with Mobil 1. At the last oil change, I noticed it had gotten really low on oil, and started to develop a tap-tap-tap while driving. It is more pronounced now, but still runs and drives great.

    The dealership said it was a deep rod knock (spun bearing) and that I needed a replacement engine.

    However, this dealership is notorious for bad/incorrect diagnoses, so I wanted to ask the Prius world out there if there was a good way to test this on my own. I realize I may be facing an engine swap, but if I could get away with just a timing chain replacement or something else, that would be great.

    I have a mechanic's stethoscope. What should I be listening for here, or what else should I be testing? The oil looks clean.

    Thank you!
     
    #1 JoeVR, Aug 19, 2025 at 1:59 PM
  2. Tombukt2

    Tombukt2 Senior Member

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    Vehicle:
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    Base
    From under car you want to get on side big block car running and listen then have some one step lightly on gas whilst ya listen at area on block wer a rod is . Obviously you gonna be doing this at different places on side o block . You will isolate . Drive it till it snaps . It mite be a long time. Keep it full of oil . I'm 20K changes making 500K pretty easily in SE heat good luck
     
    #2 Tombukt2, Aug 19, 2025 at 5:41 PM
  3. T1 Terry

    T1 Terry Active Member

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    Vehicle:
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    My taxi Prius was diagnosed with the same thing, turned out to be a block cat, the knock only occurred under load and it progressively worsened till I relented and changed the timing chain ..... it wasn't "AS NEW" but it wasn't worn to the stage the tensioner wasn't taking up the slack .....

    Test drive, still the same. Turned out the blocked cat would build up so much pressure the exhaust header pipe would compress the springs that hold is to the cast manifold, the gas would escape and the pipe would hammer back onto the manifold .......

    Fitted an aftermarket cat and a new fuel filter ..... went better than ever and was still going great when I took it off the road at 750,000 plus kms

    T1 Terry
     
    #3 T1 Terry, Aug 19, 2025 at 9:15 PM
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