Piston Soak Ideas

Discussion in 'Gen 3 Prius Technical Discussion' started by donzoh1, Sep 3, 2025 at 9:06 AM.

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  1. donzoh1

    donzoh1 Active Member

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    I recently did a piston soak using the following technique. I think the result is good but of course, I didn't tear the engine down to examine the rings afterwards.

    This was my technique:

    1. Put all pistons at midpoint of travel.
    2. Put 4 ounces of B12 Chemtool into each cylinder, allowing fluid to drain into the crankcase and through the open drain plug into a pan. (I put plugs back in loosely to control evaporation.)
    3. Filter the used fluid with a coffee filter and repeat several times.
    4. With cylinder one at BDC on compression, I added B12, replaced spark plug, and rotated the crankshaft 180 degrees with a breaker bar. The bar initially turned pretty easily but soon got very difficult to move, although I was able eventually to get it to TDC.
    5. Repeated step 4 in the firing order.

    My theory is that the B12 softened deposits in step 2 but didn't completely remove them. In step 4, the hydraulic pressure created forced the B12 past the deposits, essentially pressure washing the piston rings and grooves. As deposits are removed, cylinder compression improves.

    I learned about this technique online from an aviation mechanic who said he has done this with horizontally opposed aircraft engines. I am guessing this has been done in cars too.
     
    #1 donzoh1, Sep 3, 2025 at 9:06 AM
  2. Mendel Leisk

    Mendel Leisk MMX GEN III

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    It'd be interesting to soak "something", say old/encrusted spark plugs, in a small jar of the stuff, see what it does.
     
    #2 Mendel Leisk, Sep 3, 2025 at 2:47 PM
  3. rjparker

    rjparker Tu Humilde Sirviente

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    Low tension rings and the piston design are the root cause of gen3 and many other Toyota engines with low tension rings.

    There is a youtube series by DIY Dave where he tried almost all piston soaks and even the original heavy duty Valvoline Restore on his low tension ring Toyota with excessive oil burning. He would try each technique and drive at least 500 miles to check the oil burning. Some like B12 helped for a short time. most did nothing.

    This was over a year period all captured in his youtube series.

    He changed the valve oil seals with no improvement.

    He ended up tearing down the engine and found the rings were free and the oil return passages in the pistons were clear. If it had stuck rings or clogged oil passages he had managed to clear them. But no improvement in the excessive oil burning.

    The cylinder walks had light vertical polishing in spots but some cross hatch remained in those areas. But nothing chemical or oil related stopped the oil burning.

    He replaced the pistons and rings with Toyota revised parts and little else and the oil burning stopped.
     
    #3 rjparker, Sep 3, 2025 at 3:02 PM
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