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Knocking on startup, time to scrap?

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by mattpew, Feb 3, 2023.

  1. mattpew

    mattpew New Member

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    Grabbed a used 2010 ~220k miles just a few months ago, car ran great, was getting >50mpg in the summer months.

    Recently fuel economy dipped down to ~35mpg. Soon after I started experiencing knocking at startup (that dissipated after a few minutes of idling).

    I've done plenty of reading, am now aware that EGR cleaning is (was...) necessary to avoid head gasket failure. Also seen plenty of reports that others have fixed this knocking by cleaning injectors / replacing splugs / PCV valve etc.

    I just took it to the local mechanic for a diag, who claims the following:

    "There are 2 noises, one from front of the transmission (possible input damper assembly) and one from the engine, possible headgasket leak, car has multiple misfires on start up".

    My questions for this forum:
    1) Should I trust this mechanics conclusions, or are independent shop owners generally not expected to be very well versed in problems with this specific make/model/year? He mentions a potential noise in the transmission, but [this guy](
    ) seems to know what he's talking about, and mentions that it's a common misdiagnosis.
    2) I had no check engine light when delivering to the shop, but now it's on. Is this cause for concern that the mechanic may have harmed something, or is it expected that once the knocking begins the misfire code will lag behind by several weeks?
    3) If the answer to 1 is "no" - would it be worth running through the cheaper maintenance checklist (splugs, injectors, etc) in an attempt to fix, or is it likely that after ~225k miles without EGR servicing that the headgasket is indeed blown?
    4) If the answer to 1 is "yes" - what would be my best course of action to sell the car? Part out separately? Take to a scrapyard? Sell to a hobbyist as a project car? I'm ~$5k into this and would be thrilled to recoup even half that.
     
  2. BiomedO1

    BiomedO1 Senior Member

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    Mechanics are like a "box of chocolates"; you never know what's inside and inside some are a load of BS. IMHO; not worth messing with - if the problem was s-plugs, injectors, coils - Why does the engine smooth out after it warms up a bit. This could be indicative of an intermittent coil, but they usually stop firing when they get hot not cold.

    Here's my internet diagnosis from what your describing above:
    1. You do have a head gasket problem; keep an eye your engine coolant level
    2. CEL usually pops up right away or a minute or two after a problem; but your head gasket problem may just be getting bad enough to turn on the CEL. An OBDII code reader will probably display P0300; misfires.
    What tests did the mechanic perform to arrive at his conclusions?

    This probably wasn't much help; but in today's used car market - I'm pretty sure you could find someone to take on this project car. As long as it's still running and you don't end up bending a rod before you pawn it off to someone else.

    Good Luck
     
    #2 BiomedO1, Feb 3, 2023
    Last edited: Feb 3, 2023
  3. ColoradoCrow

    ColoradoCrow Active Member

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    Tampa Hybrids does a head gasket job for like $2100 I think. That seems pretty reasonable and usually happens about 135K. I paid $1800 for a head gasket job on my truck and I felt it was a bargain considering it a V8. If you want to keep the car for another 10 years..I would research that. FOr sure a new EGR value, spark plugs and top end cleaning with sea foam.....or even a Piston soak might get you along for another year or two. But if you plan on keeping it long term. I would start saving for a Head Gasket job.
     
  4. mattpew

    mattpew New Member

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    Thanks for the reply. As for what tests the mechanic performed - he didn't mention, but he also refused to charge me for the diagnostic, so I'd imagine he didn't sink much more time into it than a quick listen.

    Any ideas how long the car will run under this condition, and what the eventual failure will look like (does it pose any particular danger, or will it just stop running)?
     
  5. BiomedO1

    BiomedO1 Senior Member

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    That would place the mechanic in the fairly honest category; but without diagnostic testing you can never be sure.

    I would check the coolant level every morning before startup; to gauge size of head gasket leak. Use a marker, if you have to. DO NOT keep topping off the coolant level. If the coolant takes more than a couple of weeks to empty the bottle; and the car runs fine after 1-2 minutes warm-up - it's a fairly small seepage that opens up when the engine cools down. But your playing with fire, too much coolant in the combustion chamber will cause hydro-lock and will require an engine replacement. If I was going to keep the car; I'd lean more towards an overhauled/rebuilt engine, since it already has 225K on the clock. People had punched holes in the side of their engines; because of this. The car will be much more difficult to sell and you'll loose a lot of bargaining power; if it doesn't run.

    Just my 2 cents.....
     
  6. Mendel Leisk

    Mendel Leisk Senior Member

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    Probably the head gasket sealer (poured in by seller) starting to let go. Pretty much every 3rd gen for sale with over 150K is a can of worms.
     
    Grit and bisco like this.
  7. mattpew

    mattpew New Member

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    Solid point. I figured this myself - ended up selling it within a few days on FB marketplace (fully disclosing the issue) for ~$3,000. My net loss here was <$2,000, I guess it's an expensive lesson. Thanks for advice.

    I'd like to think the seller I got it from was honest. He didn't seem like a very mechanically inclined person - but perhaps he was just playing dumb when I was yapping about the EGR and asking if it was ever serviced. In any case, I'm happy it's no longer my issue to deal with.
     
    Mendel Leisk likes this.
  8. C Clay

    C Clay Member

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    That's a bargain in my opinion. I just got quoted $3200 (Lexington, KY).
     
  9. BiomedO1

    BiomedO1 Senior Member

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    Glad to hear it wasn't a total loss...

    If your not making mistakes, your not living

    Good luck in your future endeavors...