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Hi,
I have a Rotax 912ULS, 500hrs TT, and the oil level has begun rising in the oil tank.
I assume its petrol getting into the oil, the water level is ok and no milky look to the oil.
There is also oil misting around the rear of the engine and firewall.
after flying for 45 minutes, there is about 150ml increase in oil volume.
The engine revs at 5200 in climb @ 65Kt, and straight and level with WOT, gives 5400rpm, 100Kt.
The engine is fitted to a Aeroprakt Foxbat A22LS.
Carbs have been balanced and engine runs and sounds well at lower revs.
Is the 200rpm increase from climb to S&L a bit low?
I pulled spark plugs, No 1 was quite black, all the rest were good.
I changed No 1, and after running No 1 was black again??
Any ideas?
Cheers, Lloyd.
PS. All compressions are good, 1:79 2:78 3:78 4:78, all over 80PSI on leakdown test.
  • Re: Oil increasing in oil tank Rotax 912ULS

    by » 6 years ago


    This is usually caused by diesel fuel getting into auto fuel. Use another fuel source and dump what's in the tanks. Where you normally get your fuel the tanks may be contaminated from a delivery driver who did not flush out his hoses prior to dumping auto fuel in a tank.

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


  • Re: Oil increasing in oil tank Rotax 912ULS

    by » 6 years ago


    Hi Roger,
    Thankyou for your insight.
    There is the issue of oil misting around on the rear of the engine and on the firewall!
    Also, when I removed the balance tube, the rubber/hose ends were wet inside.
    If the fuel was contaminated with diesel, would this cause blowback and oil spraying around the engine compartment?
    Cheers
    Lloyd.

  • Re: Oil increasing in oil tank Rotax 912ULS

    by » 6 years ago


    "If the fuel was contaminated with diesel, would this cause blowback and oil spraying around the engine compartment?"

    Not usually. Something may be leaking or oozing out and the air flow through the engine can spread it and make it look like it is coming from somewhere other than its source. If the oil level actually got up to the vent tube and depending on how and where that was positioned it may flow out a tad and get on the back fire wall? Just clean it up and keep an eye open.

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


  • Re: Oil increasing in oil tank Rotax 912ULS

    by » 6 years ago


    I think my question regarding"the oil level rising in the tank" might have been lost in the shuffle. How would diesel fuel in the mogas get into the oil in the engine, and if this has happened, would it show up when you sump the fuel since it is heavier than gasoline? Thank you, Dave

  • Re: Oil increasing in oil tank Rotax 912ULS

    by » 6 years ago


    I bow to others superior knowledge of the Rotax 912 engine on this one but...
    In the car world an engine that sees an increase in oil on the stick has usually got excessive bore wear, stuck or broken rings causing unburnt fuel to migrate down the bore, mix with the oil and give a perception of increased oil level. The oil misting you are experiencing also bears out my stuck/ broken ring or bore wear theory.
    Does the oil in the tank smell of fuel at all?

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