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Thread: Low Oil Pressure on 912UL

  1. #1
    ersatzavian's Avatar
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    Default Low Oil Pressure on 912UL

    Hey Kitfox crew, happy to be here!

    I bought a very fine Kitfox IV this weekend and ferried home today from KSZP to KOAK. We stopped just short at KSQL for fuel. I had some oil pressure trouble and grounded the plane at KSQL til we could sort it out.

    On takeoff today at KSZP, my buddy Dave and I saw low oil pressure - intermittent drops into the mid-20s. I noted during inspections over the last two days that the sensor wire to the oil pressure sensor was damaged, and the pressure issue was intermittent and there were no other signs of trouble, so we carried on to our fuel stop at KSQL. It recurred a few times in brief spells. For most of the flight, we had pressures in the 30s and 40s. The readings were very noisy, very likely due to the damaged wire (fluctuations of 10+ psi over a few seconds).

    Descending into KSQL, we saw pressures drop back into the mid to low 20s as we reduced power. We landed, refueled,mad some calls to get more info, did a runup, and saw the same issue. We took off and pressures dropped as low as 14 psi. We reduced power and landed back at KSQl.

    We decowled the plane, cut a section of damaged wire from about the gearbox down to the pressure transducer (insulation was broken in about 10 places, with damage to the strands inside visible, and the crimp at the ring terminal was not solid and could be moved). We crimped a new length of wire with a fresh ring terminal in using a crimp splice as a temporary fix.

    The wire harness fix corrected the noise but readings were still odd. We did a low-power runup to 2500 in parking and saw pressures steady between 26 and 28 psi, so we cowled back up and taxiied out to the runup. We ran up to 4000 RPM and saw pressures drop to about 21 psi. We taxiied back to transient and left the plane.

    Does this ring a bell for anybody? Trying to get a read on whether to dig into the oil pump, regulator, or possible obstruction in the oil system, as well as whether any of today's ops might have done latent damage I now need to address.

  2. #2
    Senior Member
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    Apr 2009
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    Default Re: Low Oil Pressure on 912UL

    I would try hooking a mechanical gauge on and see what the reading is then. That would eliminate the existing gauge set up if the same problem shows up with the mechanical gauge. (I'm guessing it won't) JImChuk

  3. #3

    Join Date
    Aug 2013
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    Angola In
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    Default Re: Low Oil Pressure on 912UL

    Hi, I had a similar problem when I updated the oil pressure ball and spring to the new rotax plunger and spring.
    I believe the problem is the new plunger is bigger than the original ball. OD.
    When the plunger lifts off its seat at low rpm no real problem, but at higher rpm and higher oil volume bypassing, the oil can’t flow around the plunger freely and lifts the plunger higher thus further reducing oil pressure.
    My fix was to machine three flats on the outside of the plunger to allow free oil flow between the plunger and the body of the pump. Worked great.
    I also tried rotax spring shims didn’t work at all.
    I would like to measure a new style pump compared to an old pump to see if the plunger bore is larger on the newer pump?

  4. #4
    Senior Member Kitfox Pilot's Avatar
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    Default Re: Low Oil Pressure on 912UL

    Quote Originally Posted by avidflyer View Post
    I would try hooking a mechanical gauge on and see what the reading is then. That would eliminate the existing gauge set up if the same problem shows up with the mechanical gauge. (I'm guessing it won't) JImChuk
    Absolutely hook up a mechanical gauge and see what your real oil pressure is. This is always the first step in oil pressure reading problems. If you do have a problem you sure don't want to ruin your engine.
    Harlan and Susan Payne
    Sold Piper Archer
    Flying FarmFox STI Kitfox N61HP
    Rotax 915is, Airmaster prop
    https://www.youtube.com/channel/UC5A...oCVUP15G0uB-Yw

  5. #5
    ersatzavian's Avatar
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    Default Re: Low Oil Pressure on 912UL

    Update: we got a mechanical pressure gauge teed into the line and sure enough the VDO gauge was bad. Replaced it and am seeing oil pressures in the high 50s to low 70s across oil temps and phases of flight. Engine's healthy!

    I plan to install the kitfox remote oil sender kit, kitfox #73500.000 as soon as I take care of a couple other minor squawks.

  6. #6
    Senior Member Kitfox Pilot's Avatar
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    Default Re: Low Oil Pressure on 912UL

    That sounds like a great end to a bad problem!
    Harlan and Susan Payne
    Sold Piper Archer
    Flying FarmFox STI Kitfox N61HP
    Rotax 915is, Airmaster prop
    https://www.youtube.com/channel/UC5A...oCVUP15G0uB-Yw

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