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Changed oil on 912ULS following Rotax-Owner procedure, Pulled spark plugs and hand propped for several minutes (since I was solo and couldn’t actually see oil pressure reading), buttoned back up and realized oil was overfilled. Drained some into an oil tote so couldn’t see exactly how much came out, forgot to actually check level again, then turned prop about 6-8 times and didn’t hear gurgle. Checked oil and it was not showing on the dipstick. 

As the sinking feeling set in that I may have overdrained, then forced air into the system requiring a purge, I decided to see how much oil it needed to get back on the dipstick. I added 3/4 of a quart and was suddenly overfilled again so oil must have just been below the dipstick. 

The ultimate question here is am I OK to skip purging? It seems like ultimately I drained less than a quart before hand propping, but I don’t want to miss something and have a big mess on my hands. Sanity check please.

P.S. I did another hand propping after adding oil again and got the gurgle.

  • Re: Prop turned with oil tank 3/4 of a quart low

    by » 5 months ago


    The opening of the oil pick-up pipe in the oil tank is much lower than the bottom of the dipstick so I doubt that you have sucked in any air.


  • Re: Prop turned with oil tank 3/4 of a quart low

    by » 5 months ago


    hi William

    I think you are mistaking purging for something that is needed each oil change, it is not.  Purging is only required if you lose oil from the oil suction line to the oil pump.  If there is no air and has not been drained you only need to "vent" the engine by turning the prop.  Venting should be done with the spark plugs in place.  When turning the engine it is the crankcase pressure created by piston blow-by gases that pushes the oil from the crankcase back to the oil tank.  Be sure when you are venting, with the spark plugs in place, that you turn the prop slowly and hold the prop in the compression position and let it bleed off enough that you fall through into the next compression point.  It takes pressure from compression to work, not speed on the prop.  The number of turns is significantly less that the method shown with purging.  

     

    The process shown in the videos is called purging and should be done when you have empty oil lines or oil cooler from the oil tank to the oil pump.  The oil burping is only heard when you have the oil tank cap off and the spark plugs in place so blow-by is pushing the oil back to the oil tank from the compression gases.  

    Cheers

     


    Thank you said by: RotaxOwner Admin

  • Re: Prop turned with oil tank 3/4 of a quart low

    by » 5 months ago


    Clear on difference. The plugs out, fast prop turning was based on page 9 “Priming” being “worth it” in the article below, but maybe not necessary? Seems everyone out there is an expert on 912 oil changes and they all do it a different way. Picked a seemingly sensible source/process a while back and it hasn’t failed me, but things got a little messy this round. Too much in one day. http://lotnik.org/pliki/158_rotax-912-servicing.pdf


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