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Thread: Oil Pressure Problems

  1. #1

    Oil Pressure Problems

    I need advice on what to do, if anything, about an oil
    pressure "problem" in a Lycoming IO-360, fixed pitch prop, Phillips
    20W-50 oil.

    A few weeks ago, my oil pressure gauge suddenly read right on the
    line between yellow and green at criuse RPM (2300 - 2600). No other
    symptoms - oil temp was fine, no vibrations, fluctuations, etc. At
    idle, it read just below the yellow. I high-tailed it home and let
    the local (not very good) FBO look at it. The A&P said the capillary
    tube was clogged. He cleared the line. After that, the pressure was
    higher, but still marginal, in my opionon. It read just into the
    green at cruise RPM. So, I asked them to increase the pressure. They
    added 2 washers to the oil pressure regulator. Then the pressure
    readings returned to what I considered normal based on 5 years of
    flying this plane.

    Now, the oil pressure is suddenly reading high. At cruise and at
    normal oil temperature, the gauge reads just below the red line.
    It's not pegged, but it is steady almost at the max. Again, no other
    symptoms. Just reading too high.

    If I need to do anything, I'd like to take it to my good A&P at
    another airport. But is it safe to fly it? Why suddenly too high?
    Was the capillary still clogged and now it's clear? Any other
    advice?

    Thanks!!

    Steve Robertson
    N4732J 1967 Super III





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  2. #2

    Oil Pressure Problems

    >Now, the oil pressure is suddenly reading high. At cruise and at
    >normal oil temperature, the gauge reads just below the red line.
    >It's not pegged, but it is steady almost at the max. Again, no other
    >symptoms. Just reading too high.

    If its not over the redline, then its not too high. It has been determined
    that running the OP as close to redline as practical is better for the
    engine, specifically the exhaust guides which are fed by hydraulic lifter
    bypass oil. More pressure, more leakage past the lifter bodies, therefore
    cooler and better lubed exhaust guides. As you will find when reading from
    the articles at the following link, Cessna upped the redline on their
    engines, and then picked the OP off at a location that has a lower pressure
    than the pump outlet, where all the rest of the fleet read it. This
    effectively moved the Cessna OP to 125 PSI or more!

    http://www.prime-mover.org/Engines/Marvel/index.html

    >If I need to do anything, I'd like to take it to my good A&P at
    >another airport. But is it safe to fly it? Why suddenly too high?
    >Was the capillary still clogged and now it's clear? Any other
    >advice?

    You really need to Tee in a known accurate gauge and confirm that the panel
    mounted 30+ year old gauge is even close. If you find a large discrepancy,
    Airparts of Lock Haven (PA) can OH your gauge and re-certify it.

    www.airpartsoflockhaven.com

    Bob Steward, A&P IA
    Birmingham, AL



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  3. #3

    Oil Pressure Problems

    Thanks for the info Wes. "Capillary" was my mistake. The A&P that
    worked on the plane, though not the best, called it an oil
    pressure "line", which is the correct term.

    Best,

    Steve Robertson
    N4732J 1967 Super III

    --- In musketeermail@yahoogroups.com, Wes K <wsknettl@...> wrote:
    >
    > Bob is right on in his advice.
    >
    > I want to add that a very common cause of a sudden drop inoil
    pressure
    > folowed by a washer adjustment of the relief valve followed by a
    sudden
    > increase is the lodging of a foreign object on the ball, piston or
    seat
    > of the relief valve which causes the low pressure to suddenly
    appear.
    > The relief valve adjustment tried to compensate for the leak past
    the
    > ball. Then the foreign debris flushes itself from the ball, piston
    or
    > seat and voila very high oil pressure as the valve no longer has a
    leak.
    >
    > Another step you need to take is to open the strainer or filter
    element
    > and look for a sudden increase in metal debris. Then your A&P
    should
    > disassemble clean and thoroughly inspect the ball / piston and
    it's seat
    > for nicks. The seat is usually easy to clean up but the ball if
    nicked
    > will need a replacement. Then return the valve to it's original
    setting.
    >
    > Not sure what capillary tube your local guy is referring to. The
    oil
    > pressure gage uses plain old fashion aluminum tubing. A capillary
    tube
    > is generally found on temp systems and cannot be opened and
    cleaned in
    > the field.
    >
    > Wes K
    >






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