Bad Prop Seal or Exhaust Buildup? Please help!

Discussion in 'Outboard Maintenance' started by Fowlmouth0824, Feb 13, 2014.

  1. Fowlmouth0824

    Fowlmouth0824 Well-Known Member

    Ok so I've got an 06' Merc 9.9 2S. Bought it used, was in great condition. Motor is running strong, starts and idles well.

    After a few trips and daily flushing, I noticed a buildup of a black, stick, almost grease like substance on the waterline in my flushing bucket. Has a thick consistency, almost like grease, and smells like fuel oil.


    I've been researching and learned that these 2 strokes are notorious for expelling unburned fuel/oil through the prop and causing a build up like this, but I wouldn't expect it to be this much. While checking this out I also noticed this same substance coming from a port that is on the shaft below the cowling.


    So just to be on the safe side I decided to drain my LU oil and check its condition.
    First thing is I don't believe there was as much gear oil as there should have been. I changed the oil about 5 myths ago. Second thing I noticed it is consistency,im Not sure if this is what's considered "milky" but I'll let the pics do the talking.

    I do believe it may be a prop shaft seal. And after talking with a Merc Tech, based on what I told him he agrees.

    What else may be causing this if not a prop seal?
    What else can I do to confirm this may be the problem?
    If it is a prop seal, can it be replaced without removing the LU?

    Thanks for any input or insight that can be provided.
  2. Fowlmouth0824

    Fowlmouth0824 Well-Known Member

    And while sitting here thinking about it I decided to pull the plugs and check to see if I had a no fire. Figured if there's a misfiring plug all the gas/oil that's going in to the cylinder and not burning could cause the amount of build up im seeing.
    Here's the Plugs #1 & #2 respectively.

    My inexperienced eyes are telling me thats water on the #2
    plug. Which I know the source of now after checking my gas can and discovering that a small amount of water has somehow made it into the tank.

    So my guess is that:
    water in gas = mis firing plug
    Misfiring plug = fuel/oil not being completely burned
    Fuel/oil not burning = excessive build up of F/O on inner prop.

    Sound about right?

    What this doesn't explain however is the consistency and lack of gear oil. Could both of the problems coincidentally arose at the same time? Mabey a bad seal and misfire?

  3. Brett

    Brett > PRO STAFF <

    Goop in the bucket and bleeding from the exhaust is unburnt fuel/oil mix.
    Old technology 2 strokes at low rpm's leave up to 40% of the fuel mix unburnt.
    Coats the inside of the exhaust housing to trickle down and out later,
    or leave a ring in y'er bucket.

    Lower unit needs checking and a lube change, not really looking all that bad.
    Make sure to follow refilling instructions exactly for best results.
  4. Looks to me that it could be a number of things, either you mix ratio is too rich, your carb is running to rich, or you are idling for hours at a time, but the carb can be adjusted for that and shouldn't be that bad, also it could be because your motor was only running on 1. Lower unit fluid doesn't look bad a lot of times if you drain the oil and move the motor water will drip from random places on the motor and drip into the bucket and make it look a hair milky.
  5. mark_gardner

    mark_gardner I Love!

    this is what I would do:
    1.dump all fuel, clean and dry tank
    2.replace spark plugs
    3.drain and refill lower unit from the bottom up to insure proper amount is added
    4. wipe everything down
    5.kiss your wife and tell her how beautiful she is :D
    6.grab your rods and head for the hole ;)
  6. permitchaser

    permitchaser I Love Skinny Water

    When I had water on plugs on my old DF150 there were cracked cylinder walls. I hope that is not your problem :p