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Question about oil pressure and when it bypasses

in 912 / 914 Technical Questions 6 years ago

  • Re: Question about oil pressure and when it bypasses

    by » 6 years ago

    Hi Bill,

    I took a 30 sec video of what I was seeing.

    After you mentioned that there could be a kink in one of the hoses and I looked at them, I thought for sure that was the issue.
    (Took video of it also)

    I did throw the mechanical oil pressure guage on just to be certain and sure enough, that one was reading steady 35 psi at around 4000 rpms.
    (Took video of that also)

    With mechanical guage on, I ran it up to 5800 and it was a steady 40 psi. (Didn't video that)

    https://photos.app.goo.gl/57sNJEnfjzyc4K7o9

    I had the guage out the other day and don't remember a black wire. Will double check.
      
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  • Re: Question about oil pressure and when it bypasses

    by » 6 years ago

    If I interpret the Videos correctly, it looks like that as you increase RPM, the Mechanical Oil Pressure indicates above 40 PSI and the electrical Oil Pressure drops below 30.
    I would track down the Black ground wire at the gauge.

    Installation Manual.
    https://www.aircraftspruce.com/catalog/pdf/10-02417install.pdf


    [quote]If it makes absolutely no sense and appears that Magic is at play, It is a Grounding problem![/quote]

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

      
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  • Re: Question about oil pressure and when it bypasses

    by » 6 years ago

    Thanks for the link.

    I did track down the black wire.
    Looks like all the black wires for all the gauges are soldiered together and electrical taped. Then one wire goes to the ground bus under dash and the other goes through the firewall.

    Nothing is broke.
    I will clean the connection at the bus and add an additional ground that jumpers out the soldiered connection.
    Anything else I should try?

    If it is the ground, wouldn't all other gauges be messing up also?

    Thx again for all your help!
      
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  • Re: Question about oil pressure and when it bypasses

    by » 6 years ago

    Is the sender a 1 wire or a 3 wire device.
    If a 1 wire device, the return is through the block and the ground may be floating.
    As the RPMs come up, the ground voltage rises above Zero, making the sender appear to be going down.

    And , No it doesn't make any sense to me either. :unsure:

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

      
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  • Re: Question about oil pressure and when it bypasses

    by » 6 years ago

    No. If it is a 2 pole sender it needs it's own ground. If it is a 1 pole sender it gets its ground from the engine and that's one reason if you have a single pole sender to not apply Teflon tape. If you have two sender just attach an alligator clip to the ground on the sender and then to a known good ground and start the engine. If it is a single pole sender attach the clip right to the sender body's edge.
    If this fixes the problem find the bad ground.

    Plus like Bill suggest you can always double check the system with a mechanical gauge just plumbed in. You can buy all the few parts you need for this ate Ace Aviation (Ace Hardware). You don't need anything fancy you're just going to take a quick look to see if everything is saying the same thing. Use tiny 1/8" tubing. At the end where the gauge is just leave it a tad loose and start the engine. The pressure will purge the air out of the tube and when you see a drop or two of oil come out around the gauge threads snug it up. Now all the air is out. Piece of cake.

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

      
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