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Oil psi drops the higher I climb

in 912iS Technical Questions 7 years ago

  • Re: Oil psi drops the higher I climb

    by » 7 years ago

    Thanks Bill, I thought there might be some governor leakage, but it can’t be the problem with an electric propeller anyway. Yes, I guess the pressure and temp should be inversely related, but so much change on an engine that’s supposed to rev 5000rpm all day? You are right, maybe the regulator is busted.

    The latest 912 iS operating manual states the oil temp limit is 130C and the min oil pressure is 29 psi so I guess the oil system should be capable of making that pressure at that oil inlet temperature - and it should have enough pump capacity to achieve this as the engine approaches its TBO! Not just on a relatively new engine.

    That, I guess, raises the question, if there is nothing wrong with the oil system outside the engine, that something like a bearing or lifter? has failed.
      
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  • Re: Oil psi drops the higher I climb

    by » 7 years ago

    In regards to a port you could possible get leakage thru the wire strands going into the sensor, but as Bill notes and I see with my 912-ULS also pressure is relative to oil temp on these motors.
      
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  • Re: Oil psi drops the higher I climb

    by » 7 years ago

    Over100°C Oil at Over 5000 rpm is typically in the 40psi range.
    If you have a blown bearing or lifter you would know about it in short order.

    I would have a close look at the Oil Regulator.
    If the end of it does not make a good fit with the seat, it will not be able to raise the pressure and the Oil Viscosity will become the controlling factor.

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

    Thank you said by: Mike Blackburn
      
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  • Re: Oil psi drops the higher I climb

    by » 7 years ago

    Over100°C Oil at Over 5000 rpm is typically in the 40psi range.
    If you have a blown bearing or lifter you would know about it in short order.

    I would have a close look at the Oil Regulator.
    If the end of it does not make a good fit with the seat, it will not be able to raise the pressure and the Oil Viscosity will become the controlling factor.


    Thanks Bill - You are correct that the goodness of fit is much better between Temp and pressure. I should have tried high altitude cruise at lower power settings to rule this out - I was a bit twitchy about the low pressur eto stay up there but will do a test and see if I can replicate the pressure/temp curves.

    here is another flight which also seems to concur with your theory
    another flighthttps://www.savvyanalysis.com/flight/3075459/a87bcc2c-e7ed-46e7-8401-ab5df282f963#
      
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  • Re: Oil psi drops the higher I climb

    by » 7 years ago

    Another ref point. Yes high oil temp for sure lowers the oil pressure. Hot day summer I typically climb 4700 to 10,000 and oil temp pushes 255 F. WOT starts to drop or hold steady around 9000. Oil pressure goes lower for sure but not out of range.
      
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