Long-time intermittent rattle/shaking suddenly became nonstop

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by Iketorz, Nov 3, 2025 at 5:16 PM.

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  1. Iketorz

    Iketorz Junior Member

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    Yours is the best guess so far and explains a lot.

    But just to be clear here you're saying that my car's head gasket has been blown more or less the same amount from 100,000-201,000 miles, only showing up for a few seconds every few months in the exact same way, never better or worse than before, spark plugs at 185,000 miles came out all identical, ran normally all the rest of the time, and then at 201,000 it blew all the way, without losing any more coolant, no steam out the exhaust, no exhaust in coolant, no coolant in oil, and which goes from absolutely horrific shaking to back to running totally normally as soon as I put it in neutral, and that all of this is very common even though I've never seen a single other thread on here that's anything like this.

    Like I've said, I've blown plenty of head gaskets on other cars. I've never had one that acted like nothing was wrong if I put the car in neutral. They kept shaking away no matter what I did.
     
    #21 Iketorz, Nov 4, 2025 at 9:36 PM
  2. PriusCamper

    PriusCamper Senior Member

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    Yeah... My boss has paid for headgaskets in 3 of his Gen3 Prius and he said to me recently, "when it fails, you'll know." As in no need to worry about it until the engine runs rough all the time. And seems like avoiding hot weather and making sure that crappy electric water pump doesn't fail, as well as having clean EGR is what puts it off for as long as possible.
     
    #22 PriusCamper, Nov 4, 2025 at 9:55 PM
  3. rjparker

    rjparker Tu Humilde Sirviente

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    You are not going to get it to go away now unless you start dumping sealer in the coolant. Which is a very bad idea since heater cores and radiators often clog and need to be replaced. I suspect your car already had sealer long ago.

    You have not been reading the right threads. Most of my response above was copied from earlier posts of mine. I also have throw down videos on the subject which have been posted tens of times.
     
    #23 rjparker, Nov 4, 2025 at 10:31 PM
  4. Iketorz

    Iketorz Junior Member

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    You're saying these threads and videos are about cars that have had once-in-a-blue-moon blown head gasket symptoms for a few seconds each, for 100,000 miles, but otherwise run fine, suddenly blow completely when in gear or in park but run totally normal when the transmission is in neutral.
     
    #24 Iketorz, Nov 4, 2025 at 10:55 PM
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