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912 - Fuel in Oil

in 912 / 914 Technical Questions 6 years ago
I went to burp my 912 engine and prop would not turn. I waited a moment and was then able to turn blade one time and suddenly oil and fuel poured out on to hangar floor. The cover was off the oil tank so I believe that's where the spill originated. I found fuel in oil tank up to the rim. I had left fuel fuel valve open in plane while it sat for three weeks due to bad weather. I don't aways remember to close fuel after a flight but this had never happened before.
What could have caused this and and what should be done? Thanks for any help you can give me in this matter.

  • Re: 912 - Fuel in Oil

    by » 6 years ago

    A classic issue.

    For whatever reason, a carb float valve did not seal completely.
    Fuel flowed under gravity pressure into the carb bowl.
    it overflowed through the carburetor, into the intake manifold.
    Whichever cylinder stopped with the intake valve in the open position filled with fuel.
    The fuel slowly dribbled through the gap in the ends of the piston rings into the crankcase.
    Over time, the crankcase acquired a few quarts of fuel.

    Be happy you tried to "Burp" the engine before you tried to start it.
    Cranking a cylinder full of Non-Compressible Gasoline can do real damage.
    Hand propping the engine before the first start of the day is never a bad idea.
    One turn of the prop will tell you all you need to know.

    The cylinder full of gasoline was blown into the muffler.
    The good news is that exhaust gas is depleted of its oxygen, so when you start it the first time it will be unlikely that you will have a 15 foot flame shooting out the exhaust pipe.
    It is still a very good idea to have a fire extinguisher in someone's hand for the first start.
    Expect to see a Lot of smoke until it gets really warmed up.

    When you burped the engine, you Burped all that excess gasoline into the Oil tank and it overflowed.
    The bad news is that all your oil is now full of Gasoline and will need to be replaced.
    Drain and Clean the Oil tank and Oil Lines lines and perform a complete Oil change with Purge.

    After all that, find out why the float valve did not seal. Heavy Floats???
    I'll bet you never forget to turn the fuel valve OFF after this mess.

    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Clicking the "Thank You" is Always Appreciated by Everyone.

    Thank you said by: RotaxOwner Admin, jules rosenberg
      
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  • Re: 912 - Fuel in Oil

    by » 6 years ago

    If you have a high wing you should always turn the fuel valve off when done flying for the day.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell

    Thank you said by: jules rosenberg
      
    Report

  • Re: 912 - Fuel in Oil

    by » 6 years ago

    I am inclined to turn the fuel valve off after a day of flying (with hi wing), but I also hear that over several weeks of sitting, the fuel will evaporate from the float bowls and dry out the gaskets and seals, which can cause leaks and varnish to occur. Therefore I am wondering whether it might be better to leave the fuel ON if it is going to sit for weeks, such as in winter. I agree a hand prop is always mandatory before the first start of the day.
    Thank you said by: jules rosenberg
      
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  • Re: 912 - Fuel in Oil

    by » 6 years ago

    There would seem to be a much larger disadvantage in leaving the fuel valve open on a high wing what with fuel potentially leaking onto the floor or into the oil and causing a significant fire hazard. It'll take years to dry out gaskets and seals enough to cause a problem.

    Alan
      
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  • Re: 912 - Fuel in Oil

    by » 6 years ago

    I agree. Shut you fuel off.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell

      
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