Knocking or Heat Shield

Discussion in 'Gen 2 Prius Technical Discussion' started by Ecologically Speaking, Dec 16, 2019.

  1. Ecologically Speaking

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    Hello! Is it possible my Gen2 prius has very bad knock? or is it just more likely that a heat shield is rattling? Only possible thing I can think of is that the dealer just changed the coolant about 5,000 miles ago (currently at 140k). I don't have any OBD2 scanning devices to read coolant temps, but the fan rarely kicks on. It's winter here in Pennsylvania and doesn't get much warmer than 40*
     
  2. Ecologically Speaking

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    To clarify, this only occurs under very high load (steep hills) and half throttle. Higher throttle makes it louder, it is a metallic rattling sound coming from the passenger side of the engine bay.
     
  3. Mendel Leisk

    Mendel Leisk Senior Member

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    Try higher octane for a tank, might be carbon build-up, pre-igniting the fuel/air mixture. How many miles on it?
     
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  4. oldtechaa

    oldtechaa Active Member

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    Mine has the same. It's generally said to be knocking. I haven't done anything about it yet. Look for a thread with a title containing "medium acceleration", maybe "rattle", and you should find a video someone made that matches mine perfectly.

    My plan is likely, after replacing spark plugs, use some Berryman B-12.
     
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  5. Ecologically Speaking

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    It has 140,000 miles of varied highway and city driving. I was thinking of using some redline. I used 87 octane (middle grade here in the States) and it's already running a bit better.

    I'll take a look into that. I'm saving to get myself a torque wrench so I can install some new sparkies.
     
  6. Ecologically Speaking

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    My previous car was a Mustang and I was paying 40USD per gas tank, now I'm paying 15USD with this Prius! I love it, and I can afford higher octane gas.
     
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  7. Mendel Leisk

    Mendel Leisk Senior Member

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    If the higher octane reducing the noise, it could then be carbon build up in the head, both increasing compression slightly, and providing little glowing (pre)ignition sources. In that case a SeaFoam soak might help?
     
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  8. Ecologically Speaking

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    Running the 87 for a few days now and the sound has almost disappeared. I will run Seafoam intake spray and some Redline fuel additive and see how that helps me.
     
  9. oldtechaa

    oldtechaa Active Member

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    Are you sure you only went to 87? Very few places in the US have 85, and the Prius manual says to use 87 anyway. According to Wikipedia, 87 is considered "regular" and 89-90 "mid-grade" in the US. Mine knocks slightly even on 87.
     
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  10. Ecologically Speaking

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    My bad, I am using 89.
     
  11. oldtechaa

    oldtechaa Active Member

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    OK, good. If anyone does commonly use 85, which does exist some places, and they have knocking, the obvious choice there would be to climb to 87. For the rest of us, though, we might want to address the underlying problem like carbon in the chamber like you're planning on.
     
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