The Great Steel Seal Question Revisited

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by 6079smithw, May 27, 2026.

  1. 6079smithw

    6079smithw Junior Member

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    Hello all, looking for advice. I have a 2009 just 18 miles short of 330,000 miles. In the past month it's
    developed a minor head gasket leak; I say minor as although there are tiny bubbles in the coolant that
    pressurize it to the point it pushes the coolant out of the expansion tank there is no sign of contamination
    of either the oil or coolant (nothing on the dipstick/oil filler cap, no white smoke from the exhaust etc.)
    Ive replaced the water pump, thermostat and radiator within the last 1500 miles.


    I know replacing the head gasket is the proper fix, however, given the age and the mileage on the engine, in addition to cost, it’s not the most practical solution. I don’t want to get rid of the car because it is in excellent condition otherwise, so I have decided to throw a Hail Mary and look at some chemical solutions before I wave
    the white flag.


    From what I’ve researched it seems that Steel Seal, although expensive, seems to do the best job. I’m asking for your opinions, experience, pros, cons, caveats. i.e. input Has anybody done this? How did it work for you? Do you have any other suggestions? Any experiences, positive and negative will be appreciated.

    Thanks In Advance, Frank in Reno NV
     
    #1 6079smithw, May 27, 2026
  2. PriusCamper

    PriusCamper Senior Member

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    Can you explain how a headgasket failure pumps air into the coolant system? Not exhaust, not oil, but air? Not clear on how this would work?
     
    #2 PriusCamper, May 27, 2026
  3. ChapmanF

    ChapmanF Senior Member

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    Did anything in the OP suggest it has to be air and not exhaust?

    I guess it does say "no sign of contamination of ... coolant", but it doesn't say whether that was judged with a chemical test that would distinguish air from exhaust.

    The air-fuel mix on the compression stroke can reach 150ish psi before being ignited and turned into exhaust, which is several times the cooling system pressure, so I wouldn't be totally surprised for some air to make it across. Naturally, if the engine was firing, I would expect exhaust also, and in greater quantity because that pressure is higher.
     
    #3 ChapmanF, May 27, 2026
  4. PriusCamper

    PriusCamper Senior Member

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    he said bubbles... I thought I saw it tested as no exhaust in coolant, but either I misread or they edited what they said. Seems they'd want to test if there's exhaust in their coolant to diagnose, not just oil and coolant?
     
    #4 PriusCamper, May 27, 2026
  5. 6079smithw

    6079smithw Junior Member

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    My mistake! I did the chemical test to determine it was exhaust, what I meant was there was no indication of oil in the coolant or vice versa. Sorry.
     
    #5 6079smithw, May 27, 2026
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  6. PriusCamper

    PriusCamper Senior Member

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    Thanks for your follow up to give more details... I think we can all agree that its a fools errand to only rebuild the top end of a 330K mile engine. If you want a custom rebuild for improved performance Skimmilkhybrid.com could do that. But there's plenty of Gen2 Prius engines available at most wreckers. Getting one you can verify mileage of is the hard part. As for swapping, these 2 guys with no former Prius experience swapped out a Gen2 engine in six hours after they got home from a hard day's work:

     
    #6 PriusCamper, May 28, 2026
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