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Question about oil pressure and when it bypasses

in 912 / 914 Technical Questions 5 years ago
Hi all,

Now that my leak is fixed and I'm flying, I noticed the oil pressure dropping from 35 at 2000 rpms to 25 at 3000 rpms when I was waiting for it to warm up yesterday.

As the rpms are raised the pressure goes down, I'm assuming this is from the bypass?

On take off, pressure was going down to 25 psi and for a short field takeoff, climbing at Vx and 950ft per minute, pressure dropped to 20 psi. When I leveled off it was in the green again

The guage on my plane is yellow from 30 psi to 12, then red. Because it was in the yellow, I was concerned.
I checked the operators manual and min is 12 and I believe max was 70.
Is hitting 20 psi normal for takeoff?

I have the old bypass bolt, should this be replaced to the new style with the cone instead of the ball?

I also have some fluctuations every 5 or 10 seconds during warm up, nothing like the video on here. So I tightened all the ground screws. Are these fluctuations normal also?

Sorry for so many questions, since it's new to me I don't what her normal is yet.

Any input would be appreciated!
Thank you
IMG_20190221_133748.jpg (You do not have access to download this file.)

  • Re: Question about oil pressure and when it bypasses

    by » 5 years ago

    The Oil Pressure Regulator typically opens to limit the Oil Pressure to the 40-50psi range.
    The pressure should change slowly with temperature or throttle but generally will be as steady as a rock.

    At a Warm/Hot idle, the pressure will drop because the engine is using all the Oil the Pump is delivering.
    The 12-30 Yellow band is OK below 3500 rpm.
    Above 3500 rpm you should ALWAYS be in the GREEN. (30-70psi) (Typically 40-60)
    20psi or anything below 30psi at full Takeoff Power is an ABORT indication.

    You may have a restriction in the Oil Pump Input line. (Oil Tank >>> Oil Cooler >>> Oil Pump.)
    Look for Kinged, Crimped, Collapsed Hoses.
    Any leak will draw in Air, not spray oil.
    These hoses are under Suction, Not Pressure.

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

      
    Report

  • Re: Question about oil pressure and when it bypasses

    by » 5 years ago

    You may also just have a poor ground. This is a symptom of a poor ground. I have fixed many by just tightening the grounds.

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

      
    Report

  • Re: Question about oil pressure and when it bypasses

    by » 5 years ago

    Thx Bill,

    I will double check the input side.
    Everything I remember was really gradual bends.

    The oil tank is on the pilots side firewall --> thermostat on passenger side --> oil cooler on passenger side firewall (inlet/outlet sideways, not up) --> oil pump.

    Seems like it's a longer run than normal.
    Aren't most oil coolers in front of engine?
    If so, could it be the long run?

    If I can't find any leaks or kinks, next step would be to remove the oil sender and put an oil pressure guage on it to determine if the electric oil pressure guage readings are accurate and go from there?

    Thx
      
    Report

  • Re: Question about oil pressure and when it bypasses

    by » 5 years ago

    Thx Roger,

    When researching if this was normal, I did come across one of your posts that state a ground might be the cause. So I tightened all the grounds on the bus.

    Any other place? Or can I add one temporarily to see if it helps?

    If I remember correctly, 2 purple, white, and red were in the back. The white went to pump, would the red or purple be ground?
    Or is the mount grounded?

    Thx
    IMG_20190301_153444.jpg (You do not have access to download this file.)
      
    Report

  • Re: Question about oil pressure and when it bypasses

    by » 5 years ago

    Standard UMA Gauge colors...
    2x Violet = Internal Gauge Lighting.
    White = Signal from Pressure Sender
    Red= 12v Power
    Black = Ground

    Remember that the Engine mount is Rubber cushioned and does Not naturally Ground the Engine Block to the Airframe.
    The Ground cable for the starter to the battery usually serves the function of grounding the block to the Airframe.

    Temporarily installing a Fully Mechanical Pressure Gauge is worth the effort to verify that the problem is real or the indication is false.

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

      
    Report
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