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Onan 6.5kw MCCK Generator - Blows carbon and Oil blackens over time

Discussion in 'Generators' started by lslifkin, Sep 1, 2015.

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  1. lslifkin

    lslifkin New Member

    Joined:
    Aug 30, 2015
    Messages:
    4
    Location:
    Stamford, CT
    We have a 1985 era Onan 6.5kw MCCK generator. Recently, i have noticed that the Oil is black in color and smells a bit fumy. I have cleaned the breath filter and cap - No real change. This past weekend, I noticed that when she was started (and she always starts and runs great), a black oily/sooty film came out. I listened to the gen set and decided that she should be powered down. I will be going to change the oil, re-check and clean the breather filter and cap, check spark plugs for fouling and run Seafoam through her to clear any possible build up.

    Has anyone come across this with either an Onan or similar generator?

    Thanks in advanced to those that reply...

    - Larry S -
  2. Capt Ralph

    Capt Ralph Senior Member

    Joined:
    Sep 8, 2004
    Messages:
    8,287
    Location:
    Satsuma, FL
    Over filled oil, thin oil (you smelled something), worn rings.
    This is the opposed 2 lung model. Started life as an air cooled unit and like Ferryman, added water cooled cylinder jugs for enclosed use.
    Make sure the engine is level and not leaning towards one of the cylinders.

    Start it for a half second. pull the plugs. One or both will probably be oil wet.

    Your sump may not appear to low because that's gas taking the oils place hence the bad smell.

    Try a straight 30 or 40w oil.

    Start your Good Boy letter to Santa now.
    Or as I do, couch dive every chance.
  3. lslifkin

    lslifkin New Member

    Joined:
    Aug 30, 2015
    Messages:
    4
    Location:
    Stamford, CT

    This is the results of yesterday's work.... Changed Oil - used 15W-40. Pulled plugs - Very carboned - Cleaned. Plugged breather filter and cap - Oily - Cleaned and replaced. Started Gen. Gen ran well - Used Seafoam. Seafoam did not seem to make a major difference.

    As for the mounting of the Gen - Been the same way for 29 years without issue. So i do not believe that is it... Plugs have not been terribly wet, or no more than normal.

    Any other thoughts?
  4. Capt Ralph

    Capt Ralph Senior Member

    Joined:
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    8,287
    Location:
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    Seafoam (snake oil) in the gas or oil?

    Try straight w oil.
    Start couch diving at your friends house.
    Brush up on your letter writing skills,
    Dearest Santa
    Is a good start..:)
    ,rc
  5. lslifkin

    lslifkin New Member

    Joined:
    Aug 30, 2015
    Messages:
    4
    Location:
    Stamford, CT

    I can do Straight Weight, no issue.... The Seafoam was Poured into the Carb to clean out any carbon deposits... None added to oil or fuel.
  6. Capt Ralph

    Capt Ralph Senior Member

    Joined:
    Sep 8, 2004
    Messages:
    8,287
    Location:
    Satsuma, FL
    I'm guessing the set has been running and deteriorated to this, OR storage for a while and these symptoms at startup?
    You have worn or stuck rings. Rebuild or replace.
    If really desperate to try a snake oil, pour some Restore oil additive in the sump. before you go to a straight oil W. It may just well be another waist of money but I have heard from a friend, of a friend of a friend state it will un-stick piston rings.