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  1. #11

    Re: Allison M20 over-full

    Ok, but isn't the oil cooler raw water cooled? And if so the oil would get milky, not really black correct?

  2. #12

    Re: Allison M20 over-full

    Quote Originally Posted by johnjen50 View Post
    Ok, but isn't the oil cooler raw water cooled? And if so the oil would get milky, not really black correct?
    Fresh water cooled, from bottom of heat exchanger.

  3. #13

    Re: Allison M20 over-full

    Transmission oil cooled by seawater. Engine Oil cooled by freshwater.
    Scott
    41C117 "Hattatude"
    Port Canaveral Florida.


    Marine Electronics and Electrical Products Distributor.

  4. #14

    Re: Allison M20 over-full

    But still, why would that make the oil black? Wouldn't it make it milky?

  5. #15

    Re: Allison M20 over-full

    Quote Originally Posted by Boatsb View Post
    Transmission oil cooled by seawater. Engine Oil cooled by freshwater.
    Both are fresh water cooled
    "DON'T BELIEVE ANYTHING YOU READ OR HEAR AND ONLY HALF OF WHAT YOU SEE" - BEN FRANKLIN




    Endless Summer
    1967 50c 12/71n DDA 525hp
    ex Miss Betsy
    owners:
    Howard P. Miller 1967-1974
    Richard F Hull 1974-1976
    Robert J. & R.Scott Smith 1976-present

  6. #16

    Re: Allison M20 over-full

    Fresh or salt, whatever kind of water turns oil milky. This can also give the oil the consistency and appearance of toothpaste. I don't know what this may do to the flow rate of the oil pump but I'm pretty sure it's not good.
    Jim Grove, Fanfare 1966 50MY Hull #22 (Delivered Jan. 7, 1966)

    "LIFE IS JUST ONE DAMNED THING AFTER ANOTHER." Frank Ward O'Malley, Journalist, Playwright 1875-1932

  7. #17

    Re: Allison M20 over-full

    A bad rear engine seal will give you sooty oil on an M20. I went through this drill last year and had major transmission damage requiring a rebuild at Arcadian in Louisiana.

  8. #18

    Re: Allison M20 over-full

    Did the sooty oil cause the damage? If so, what happened? Or was the cost to remove and replace the engine seal?

    I would expect that the engine oil filter would remove most of the damaging grit in normal operation. Bearings in the engine are about the same as those in the transmission. Water from combustion would be bad, but my old Allisons ran about as hot as the engines so should be boiled off through evaporation. Acids on the bearings (especially the roller bearings) could do harm but the transmission oil is the same 40 weight as engine oil and so well buffered against this, as well as there being a lot of otherwise clean oil in the transmission to dilute.

    Of course,once you get the transmission separated from the engine you might as well do the whole thing and be good for another 20 years.
    Jim Grove, Fanfare 1966 50MY Hull #22 (Delivered Jan. 7, 1966)

    "LIFE IS JUST ONE DAMNED THING AFTER ANOTHER." Frank Ward O'Malley, Journalist, Playwright 1875-1932

  9. #19

    Re: Allison M20 over-full

    My rear main seals leaked into the transmissions on both engines for 20 years and a lot of hard running. Never had a problem. I rebuilt the engines in 2002 and haven't leaked a drop (into the trans) since. I've got the MH gears tho.
    IMHO reguarding transmission failures I see a lot of people move the clutches from forward to reverse and back without stopping in neutral to slow the shafts that's a lot of mass to change direction and hard on the transmission.
    "DON'T BELIEVE ANYTHING YOU READ OR HEAR AND ONLY HALF OF WHAT YOU SEE" - BEN FRANKLIN




    Endless Summer
    1967 50c 12/71n DDA 525hp
    ex Miss Betsy
    owners:
    Howard P. Miller 1967-1974
    Richard F Hull 1974-1976
    Robert J. & R.Scott Smith 1976-present

  10. #20

    Re: Allison M20 over-full

    I doubt the oil leak and dirty oil caused my transmission failure. That being said, the transmission oil filter is totally incapable of removing the engine soot from the transmission once it leaks in. Early on, I changed the oil and filters multiple times and, just like the engine, with a leaking seal it was 'dirty' in no time. With a good seals, the tranmission oil looks brand new for years.
    You can learn much about your transmission by checking the strainer (for metal and clutch material) and cutting open your used oil filters. Mine was full of metal leading to a big overhaul. Again, I don't know if I can blame the bad oil seal but my other transmission has perfect looking oil and no metal in the strainer or filter...

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