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Hi,

I recently had the oil cooler disconnected on my 912ULS, when putting the oil cooler back on, I topped up oil levels to the full mark, however I was unaware that an oil purge is required after doing such, it took about 15-20 seconds for oil pressure to display on the gauge after initial start up and the engine ran about .5-1hr after the whole ordeal, just wondering if I should be concerned of possible engine damage and if it would be worthwhile to maybe do a purge at this point before starting the engine again?

Thank you
  • Re: Didn’t do an oil purge?

    by » 6 years ago


    If it had only run a couple of minutes I might have said do the purge. If it's been an hour you may be fine and dodged that proverbial bullet. The system can handle a small amount of air, but there is a point that it can be too much and since we have hydraulic lifters it can be an issue. Any major breach of the oil system like draining the oil cooler needs a purge. I'm a believer in better to be safe than to spend thousands fixing it when it would have just taken 30 minutes to do it right.

    Maybe Rob or Bill will weigh in and see what they say.

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


  • Re: Didn’t do an oil purge?

    by » 6 years ago


    15-20 Seconds at a cold idle is pushing the limits.
    If the engine had been run shortly before the event there was probably enough residual oil in the gallies to save the day.
    In any event, once the engine displayed oil pressure, the purge was 90% complete and 100% complete a minute later.
    After an hour of running and heat cycling, there is nothing more that can be done.
    The damage, if any, is already done.
    Consider yourself lucky.
    Next time, if you ever go 5 seconds without seeing Oil pressure, shut it down and hand prop it until you do.
    If the engine had 9 lives it now only has 8.

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


  • Re: Didn’t do an oil purge?

    by » 6 years ago


    Hi Bill, thanks for the info, the plane itself was new to me, so I actually hadn’t notice it was running without oil pressure until I saw the gauge rapidly climb up, after the event I did a fair bit of reading and realized that I should have purged the system; I’ll probably run the engine for a good hour or so to be safe and avoid a mid air engine failure. Is there anything fairly easy i can check that could have been potentially damaged without an extensive engine tear down?

  • Re: Didn’t do an oil purge?

    by » 6 years ago


    You should check the washers under the valve springs for unusual wear.
    If a lifter has been running flat (air trapped inside) the valve train will be hammering away, and the first reliable indication is wear on the washers.
    Normally, even after thousands of hours, the washers will not show any wear.
    See SI-912-018 "Purging of the lubrication system" Page 12.

    Thank you said by: Roger Lee, Andrew Dunning

  • Re: Didn’t do an oil purge?

    by » 6 years ago


    Will do, thanks, also have a differential compression tester coming in the mail in a few days, so I will do that test, and probably a direct compression check as well, I’m assuming these will give a good indication of engine health.

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