Radiator cap failure on gen2 ever happens?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by pasadena_commut, Apr 3, 2026.

  1. pasadena_commut

    pasadena_commut Senior Member

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    By chance today I stumbled upon two "Toyota Maintenance Channel" YouTube videos about radiator cap failures. The center piece broke off and fell into the radiator. Yikes. Both were larger Toyota vehicles, a pickup truck and a 4Runner (maybe, I wasn't paying close attention). So I searched here to see if anybody had ever reported a Gen2 radiator cap breaking like that. No hits in the first few pages, but "radiator", "cap", and "broke" may have put pages of unrelated hits before the relevant post.

    Do any of you recall seeing a post about a broken radiator cap on one of these cars, or seen one in person?

    I should probably change ours since it is at least 7 years old (as long as we have had the car) and for all I know it might be the original from the factory.

    Any idea what a shop would charge to pressure test just the new cap? When we changed the radiator and cap on our Accord we had a "loaner tool" pressure tester from Autozone, and used that to discover that the Gates replacement cap was defective (would not open up to a ridiculous pressure). Bought a Honda OEM one, tested it, and it opened at the specified pressure I swore I would never install another radiator cap without testing it first. The thing is, with Autozone you buy the tester, use it, return it and then they refund it, and the deposit on that unit was around $200 several years ago. I would be happy to pay a shop $20 for the 10 minutes work if it would let me skip that hassle.
     
    #1 pasadena_commut, Apr 3, 2026
  2. JC91006

    JC91006 Senior Member

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    You can get a loaner tool from autozone, it's free. If your car is not overheating, the cap is probably good.

    Or you can just buy a new cap on Amazon for a few bucks.
     
    #2 JC91006, Apr 3, 2026
  3. Tombukt2

    Tombukt2 Senior Member

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    The beast is falling off on some of these caps I don't think is on our cars it's a slightly different design cap I try n. Keep all of mine yellow tagged originals ove a few from 85 celicas they larger than ours still work fine hold pressure . Cap tester comes w rad pump tested usually now I bollet alum. That little centerpiece couldn't make it off the top row of your radiator it's got no we to go . Vacuum. It out . Can't fit any wet. Think about it . Until it disintegrated can't move
     
    #3 Tombukt2, Apr 3, 2026
  4. Hayslayer

    Hayslayer Active Member

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    nvm
     
    #4 Hayslayer, Apr 3, 2026
  5. Tombukt2

    Tombukt2 Senior Member

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    Take radiator out turn it upside down and shake it a little piece that fell off your rad cap will fall. Out. Yep cap no good now . Grab another from pile. Or junk yard. Rarely by replacements.
     
    #5 Tombukt2, Apr 3, 2026
  6. BiomedO1

    BiomedO1 Senior Member

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    In my experience; I've never had a cap disintegrate on me - they've leaked but never fell apart. I've had to replace a radiator on my dad's old Toyota SR5 truck, because the top tank seam rusted away and was leaking. The OEM cap was leaking, bottom rubber gasket fell apart and was more than 25 years old.
    IMHO; If your doing your 10 year of 100K mile coolant changes and proper inspections - you shouldn't have any problems.

    Hope this helps.....
     
    #6 BiomedO1, Apr 3, 2026
  7. mr_guy_mann

    mr_guy_mann Senior Member

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    I see it now and again on some Toyotas or Hondas when they get over 10-15 years old. Not very often, but it happens. Usually I can fish the plastic bit out, but it's small enough to not cause much harm if it stays in the radiator.

    More common would be having the rubber seals deteriorate and not seal.

    Posted via the PriusChat mobile app.
     
    #7 mr_guy_mann, Apr 3, 2026
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