I have removed and reinstalled my oil cooler on my 912S, therefore I need to purge my oil system. I watched the video on purging the oil system and all is understandable and clear to me, until it gets to the part about the oil Cooler. I have an oil temperature thermostat. This is what the video says:

"If an optional oil thermostat is installed it will by pass the oil cooler when cold; and feed the oil cooler when warm. Extra attention should be given to assure this circuit is properly purged of air."

So, how do I properly purge the oil cooler of air. How is this supposed to be done? The video is silent regarding this matter, except to say that it should be done.

  • Re: Purging Oil System on 912S

    by » 4 years ago

    The average operator is not as observant as you are and just ignores the whole instruction without incident.
    Fill the Oil cooler manually before attaching the hoses to eliminate 90% of the air if it worries you.

    The Oil thermostat does not bypass 100% of the oil. A small amount of oil always flows through the cooler.
    By the time the Thermostat Opens, the Oil Cooler will be full even if you did not pre-fill it.

    As long as you see good oil pressure on the gauge, you are good.
    A small amount of air in the oil lines after maintenance is normal and not harmful as long as the first minute of operation is performed at idle speeds.
    No "Throttle Up" is permitted until the engine reaches 50C in any event.

    After any oil change, the Pickup pipe in the Oil Tank will have air in it and the Oil Filter will only be partially full, as it is mounted on its side. All normal occurrences.

    The minimal amount of air is not a disaster as long as the oil pump does not lose its prime and the oil pressure is sufficient.
    You might see it fluctuate slightly as the initial air bubbles pass by.
    You should see oil pressure within 2 seconds.
    If the pressure is low after 5 seconds Get your hand on the switches.
    If it is still low at 10 seconds, Shut it down!

    If you saw Oil Pressure while purging it, you should not expect any problems.

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

    Thank you said by: Rob Seaton, Slavo Rodi, RotaxOwner Admin

  • Re: Purging Oil System on 912S

    by » 4 years ago

    Thank you Bill for your reply. I have not been near a computer for the past three days, and didn't see your reply until now. After thinking it through before reading your suggestions I came up with pretty much all that you said. I'll forge ahead!

    Thanks again,

  • Re: Purging Oil System on 912S

    by » 4 years ago

    have the oil cooler connections on top of the oil cooler and purge as normal. the thermostat when fully closed /cold bypasses oil approx 10% ,so it will purge the air out of the cooler and system.

  • Re: Purging Oil System on 912S

    by » one month ago


    I've a question about 912S engine. What is the purpose of use an oil tube( Item .3) inside Crankcase?



    27242_2_1.jpg (You do not have access to download this file.)

  • Re: Purging Oil System on 912S

    by » one month ago

    When I pull an oil cooler or any other oil hose  and to reduce any mess on the floor or more importantly to not loose any oil from a hose I use rubber corks. If I pull the oil hose off the cooler I unscrew the fitting and immediately put a rubber cork in the end of the hose and the oil cooler. I do that to both sides. Then I don't loose any oil. If all I do is pull the cooler for cleaning then after I clean it I just prefill it with oil. Then there isn't a purge necessary since I only lost a very tiny amount of oil. When I do a 5 year rubber change and I pull the oil hose I put the rubber corks in the fitting ends just so I don't make a mess everywhere.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-574-1080 Home (TRY HOME FIRST)
    520-349-7056 Cell

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