Intake or exhaust valve stem cap!

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by Notn2bars, Aug 2, 2025 at 5:45 PM.

  1. Notn2bars

    Notn2bars New Member

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    We have a 2012 Prius. Recently did a bunch of work on our Prius. Long story short, had to take it to the dealer because we couldn't get in running correctly.They discovered that one of the valve stem caps was missing and could not locate it. All of them were installed and everything was torqued to specs when the I replaced the head gasket. Sooooooo, where could the cap have vanished? Could it have landed on top of one of the pistons? Is there an oil passage from the top of the head to the oil pan large enough for the cap to pass through? Any other thoughts? Your help is sincerely sought and appreciated. Will be going to the dealer on Monday to see what the options will be.

    God Bless, Ed Jones
     
    #1 Notn2bars, Aug 2, 2025 at 5:45 PM
  2. ChapmanF

    ChapmanF Senior Member

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    yikes
     
    #2 ChapmanF, Aug 2, 2025 at 9:22 PM
  3. rjparker

    rjparker Tu Humilde Sirviente

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    It was left out during the hg job or it was loose and fell somewhere in the engine bay when the dealer tech opened it up. Either way it was not installed properly.

    It has happened before.
     
    #3 rjparker, Aug 2, 2025 at 10:56 PM
  4. NutzAboutBolts

    NutzAboutBolts Senior Member

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    Those caps aren’t easily removed by fluids going over it… you have to physically pull it off of the valve stems to remove it from the top. Whoever did the work removed it and forgot to put it back, I would blame the technician who worked on it last when they did your head gasket.
     
    #4 NutzAboutBolts, Aug 3, 2025 at 1:42 AM
  5. Notn2bars

    Notn2bars New Member

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    Thanks to all for taking the time to reply. I was the "tech" who replaced the head gasket:(. Not my first rodeo, very meticulous when replacing the parts. Not to say I couldn't have missed something, this is the first time working on car motors for over 55 years that something like this has happened. Anyway to my original questions. Could the cap have fallen through a valve port and be sitting on top of one of the pistons? Could the valve cap have fallen through the oil passages and ended up in the oil pan? God Bless all, Ed
     
    #5 Notn2bars, Aug 3, 2025 at 10:31 AM
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  6. Mendel Leisk

    Mendel Leisk MMX GEN III

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    You could borescope the combustion chambers to see if it's atop piston. It might also be down an oil or coolant passage?

    Or think good thoughts, that it was swept up with debris at the machine shop. :)
     
    #6 Mendel Leisk, Aug 3, 2025 at 2:43 PM
  7. ChapmanF

    ChapmanF Senior Member

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    I don't think there are any passages from atop the head into the valve ports or combustion chambers (other than the spark plug holes).

    There are passages down to the sump, but I don't know if the item could drop through them.
     
    #7 ChapmanF, Aug 3, 2025 at 2:49 PM
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  8. NutzAboutBolts

    NutzAboutBolts Senior Member

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    I don’t think it’s possible, if you look at my cylinder head, everything is closed off and too small for the caps to move past those holes. My best guess would be it got lodged into the head bolts top hole and is in there if it moved around some how. But I don’t think it’s possible for the caps to go into the top of the piston since the one way it’ll go into the piston would be through the spark plug tube. You would also definitely hear some engine issue if it’s on top of the piston.
     

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    #8 NutzAboutBolts, Aug 3, 2025 at 4:17 PM
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