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Apologies if this has been answered on here before but I can't find it if so. My question is this: if you have run your 912UL on avgas for 1000 hours, and then start to use UL91 exclusively thereafter, is there a point at which the oil change interval can be lengthened to that recommended for operating with UL91 only, or does the fact that 50 percent of the engine hours til TBO has been spent with avgas means that you will need to keep changing oil in line with the avgas only recommended interval?

In other words, what does 'less than 30 percent of the time' mean? Average over the whole life of the engine or average since last oil change? Or average over some other period between those two extremes?

Nick
  • Re: What does using avgas 30 percent of the time mean?

    by » 7 years ago


    It is generally accepted that the clock restarts at each oil change.
    If you have been on 100LL for 1000 Hours, Maybe the second Oil change.

    Assuming 4-5 gal of fuel per hour and 120 gallons and 25 hours between oil changes...
    You are at 30% once you have filled ~35 gallons of Avgas.
    35 gallons of 100LL will leave a specific amount of lead paste in the oil.
    Running Mogas after that, does not dilute or reduce the Lead in the oil.
    It just doesn't add any more.
    Warming up the engine just before changing the oil to get the lead mixed into the oil immediately before performing the oil change will help in getting most of it out.

    That said, most people do not extend the oil change period when using MoGas and continue with the 25-hour changes.
    Some might push it as far as 40 hours.
    Oil is cheap insurance.

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


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