EGR cooler nightmare event -- always check a used one for leaks before you install...

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by cdherman, Mar 23, 2026 at 11:42 AM.

  1. cdherman

    cdherman Junior Member

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    Short story: I took a running, zero issues 2014 Prius burning no oil at 148,000 miles and converted it to a blown headgasket.

    Long story: I replaced my 2011 Prius EGR cooler 4 years ago with a cleaned up, used one. The 2011 Prius is going strong.

    My 2014 Prius is headed to another state so, I decided to clean up the 2011 EGR cooler and swap it into the 2014. I completed the swap and immediately got a check engine light. It ran fine so I drove it , and started to see steam. Took the short connecting pipe off between the EGR valve and intake manifold and found coolant. Took things back apart and found a leak in the 2011 cooler. It did NOT have the leak before I cleaned it, but somehow, between my Draino and piano wire cleaning, I must have exposed or created a leak.

    I cleaned up the 2014 cooler and tested for leak -- no leak. Put things back together, but still consuming coolant and sending out steam from the exhaust.

    So the coolant from the defective EGR cooler must have caused my head gasket to fail.

    Ugh. I converted a perfectly running vehicle to a junker. Guess I will be learning how to replace head gasket.....
     
    #1 cdherman, Mar 23, 2026 at 11:42 AM
  2. Mendel Leisk

    Mendel Leisk MMX GEN III

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    Probably the piano wire. You used Draino, not just lye? Draino is a bit of a witch's brew, even has flakes of aluminum in it I think. I would use either Potassium Hydroxide (KOH) or Sodium Hydroxide (NaOH). Of the two, the KOH is likely easier to get (popular for soap making), more water soluble, and more effective.

    More info on KOH versus NaOH
     
    #2 Mendel Leisk, Mar 23, 2026 at 11:47 AM
    Last edited: Mar 23, 2026 at 12:11 PM
  3. cdherman

    cdherman Junior Member

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    Ironicaly, I cleaned the first one I bought off ebay 4 years ago exactly the same way and it was dirtier by far when it started. The piano wire is quite small and stiff. As for draino, I have been using that to clean gunk of metal parts forever and never had a problem. do not know -- clearly got unlucky on this one.

    As I said, the number one mistake was not testing a used EGR cooler. Readers should never assume a used one is good, even your own EGR cooler that you just cleaned. Cause mine was not leaking and I cleaned it and this is what I got -- blown head gaskets.
     
    #3 cdherman, Mar 23, 2026 at 6:30 PM
  4. ASRDogman

    ASRDogman Senior Member

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    It's likely you poked a hole in the cooling passages with the piano wire.
    You didn't say how many miles on the engine, but it might have just been timing.

    It's not that difficult to replace the head gasket....

    Oven cleaner and pressure washer work fast and easy and safely.
    I am going to try the drain cleaner though. Just to see, and I have a spare cooler.
     
    #4 ASRDogman, Mar 23, 2026 at 6:48 PM
  5. VelvetFoot

    VelvetFoot Active Member

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    Oven cleaner isn't just NaOH anymore though is it?
    Did you use a newer formulation?
     
    #5 VelvetFoot, Mar 23, 2026 at 8:06 PM
  6. CR94

    CR94 Senior Member

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    Yeah, leakage of pressurized coolant into the EGR stream via the cooler would soon lead to disaster on two fronts---low coolant and trying to compress liquid.

    I bought (but haven't yet needed to use) a used spare cooler on which one of the coolant pipes was bent. Therefore, I tested it extra carefully for leaks after cleaning it with wire and Oxi-Clean. No leak.

    Music wire is harder and stonger than common sorts of cheap steel wire.
     
    #6 CR94, Mar 23, 2026 at 9:22 PM
    Last edited: Mar 23, 2026 at 9:30 PM
  7. ASRDogman

    ASRDogman Senior Member

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    Oven cleaner still works....

    If the cooler leaks, inside, it goes out the exhaust.... It doesn't go into the intake manifold...
     
    #7 ASRDogman, Mar 23, 2026 at 9:53 PM
  8. ChapmanF

    ChapmanF Senior Member

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    There may be some confusion with gen 4's occasionally leaky Exhaust Heat Recovery System exchanger. If that leaks, the coolant goes out the exhaust.

    If an Exhaust Gas Recirculation cooler leaks, that's gonna go into the intake.
     
    #8 ChapmanF, Mar 24, 2026 at 12:13 AM
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  9. rjparker

    rjparker Tu Humilde Sirviente

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    It seems incredible a piano wire would bore a hole in a stainless steel egr cooler.

    Stainless steel requires low rpm, high pressure drilling and lubrication. Otherwise many types of ss will heat harden.

    Perhaps a drill bit was used first?
     
    #9 rjparker, Mar 24, 2026 at 1:14 AM
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