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Thread: Too much oil pressure?

  1. #1
    Orbiting Earth Heading to Pluto corcoran's Avatar
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    Too much oil pressure?

    Had the oil pressure go over the top of the red today... 12 minutes after T/O at 3,000'msl, 2500rpms, oil temp unknown due to sender malfuctioning always high. Landed. Oil on dipstick looked thin. Impossible to determine quantity at high temperature. I did not wait for cooling. Added two quarts to the 5qts (I think) already onboard. Ran cooler on the way back home at 2300rpms.

    Question: Can you have too much oil pressure?

    Tom Corcoran



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  2. #2

    Too much oil pressure?

    >Had the oil pressure go over the top of the red today... 12 minutes after
    >T/O at 3,000'msl, 2500rpms, oil temp unknown due to sender malfuctioning
    >always high. Landed. Oil on dipstick looked thin. Impossible to determine
    >quantity at high temperature. I did not wait for cooling. Added two quarts
    >to the 5qts (I think) already onboard. Ran cooler on the way back home at
    >2300rpms.
    >
    >Question: Can you have too much oil pressure?

    Within reason, its like being too rich or too thin. <G>

    The down side to "too much" oil pressure is that if you have a can type
    filter you can blow the gasket out or fail the crimped seal on the filter
    housing and blow out all the oil in a few seconds. You might also damage
    the sealant between the case halves if your engine case hasn't been
    modified to provide a separation between the forward and center cam
    journals and the outside of the case.

    Cessna worked with Lycoming to RAISE the oil pressure on the current
    production planes. They changed the red line on the gauge and they picked
    up the pressure at a different point on the engine where the pressure is
    known to be less than at the pump outlet, which is where the older
    Lycoming's picked the pressure tap.

    The end result is that if you measured the OP on a new C-172 at the old
    location where your Musketeer is taking its pressure reading, that the red
    line for the new Cessna is about 125 PSI, or ~25# higher than the older
    plane's gauges read it.

    For those that want a more in depth discussion, I refer you to this article:

    http://egaa.home.mindspring.com/new.htm

    Bob Steward, A&P IA
    Birmingham, AL



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  3. #3

    Too much oil pressure?

    >Is there a way to raise the maximum oil pressure? Or should I just fly
    >higher, or slower?
    >Jim C

    Within the limits of what your oil pump will flow and the clearances in
    your engine bearings, which is what creates the pressure -- excess flow by
    the pump over what the bearings leak away, Yes, you can increase the pressure.

    Lycoming has a couple different pressure regulators, one uses a stack of
    washers to pre-load a spring, and the other has an adjustable pre-load with
    a threaded external adjuster.

    Both are located above and aft of the #3 cylinder (rear on the passenger side).

    Any competent A&P (LAME in AU?) ought to be able to make the adjustment.

    Its usually a good idea to check the free length of the spring in the
    stacked washer type regulator. They have often taken a set after 30 years
    of service.

    > > http://egaa.home.mindspring.com/new.htm

    Per the article, you'll note that the goal is to get the OP as close to 100
    psi (when at operating temp) as is practical, even if that means that you
    get higher than redline pressure on start up. However if you limit the RPM
    to 1200 or less, you likely won't have any OP problems when cold.

    Bob Steward, A&P IA
    Birmingham, AL



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  4. #4

    Too much oil pressure?

    Jim, all the indicators point to severe high oil temperature. I'll bet that
    if you continue to run high power in climb or cruise, to the extent that the
    oil pressure dips just below the 60 PSI mark, you also begin to experience
    prop overspeeding beyond the set RPM.

    Do you have anything like a JPI engine analyzer, to which you can add an oil
    temperature sensor? They usually mount in the right front oil gallery on
    the Lycomings. I would bet a dollar to a doughnut that you are experiencing
    oil temperatures in the 260 to 270 degrees F range (130 C). 200 C (390 F)
    on the CHT is also significantly higher than these engines should run in
    cruise; another indication of excessive oil temperatures. Cruise CHT should
    be closer to 325 F (162 C). You need to get this sorted out soon, or limit
    your climbs and cruise to power settings that result in more normal
    temperatures. Normal oil temp for most of our applications is closer to 190
    F in cruise (88C). This is right about where the little white dot is, in
    the green on the oil temp gauge.

    You probably won't be able to load the engine enough to reproduce this
    problem on the ground. It usually takes a long hot climb, along with ten to
    twenty minutes at high-power cruise, to make it show up.

    I know you said that the Vernatherm was replaced last year. Are you 100%
    certain it was replaced with a brand-new part, as opposed to a
    used-serviceable part? Used Vernatherms should never be reinstalled; they
    have a very high failure rate if the Lycoming test is performed on them. I
    remain suspicious of either the valve or its mating seat. One member
    reported going through three rounds of valve and seat repair, before it got
    fixed. Another possibility is a partially clogged oil cooler. Southwest
    Cooler Service in Dallas, TX does good work, but you can probably find a
    closer service. Do NOT let a local technician try to flush it locally with
    solvent; that will not clean clogged passages, and is a waste of money.

    Sometimes the remote cooler setups result in relocation of the Vernatherm
    from its stock location. In turn, this usually provides the valve with a
    new seat. If you are certain that you got a brand new, good valve, and that
    it has been properly installed in a new adapter housing, and that correct
    gaskets were properly installed, you might want to start with the cooler
    flush. Particularly if there are no records showing that it has ever been
    done. It should always be done at overhaul, or whenever work is done due to
    contaminants having been found in the oil filter media (or screen)
    examination, but the coolers are very often neglected.


    _____

    From: musketeermail@yahoogroups.com [mailto:musketeermail@yahoogroups.com]
    On Behalf Of Jim Campbell
    Sent: Sunday, February 12, 2006 8:57 AM
    To: musketeermail@yahoogroups.com
    Subject: [musketeermail] Re: Too much oil pressure?

    Very many thanks for the link to that article, Bob.
    I have been suffering from what I believe to be low oil pressure/high
    temperature. I had a spin-on, firewall-mounted kit installed because
    of claims that it assisted with lowering oil temperatures but it made
    no difference.
    At this time of the year oat is 28C at 1500msl and the oil pressure at
    cruise shows neatly on the edge of the yellow segment with temp almost
    into the red. CHT is 200C. (at 2600/26mp ~13gph)
    Had the vernatherm replaced last year too.
    Of course, I notice it more when the oil and filter have been changed
    - like last week!
    Is there a way to raise the maximum oil pressure? Or should I just fly
    higher, or slower?
    Jim C


    --- In musketeermail@yahoogroups.com, Bob Steward <n76lima@...> wrote:
    >
    >
    > >Had the oil pressure go over the top of the red today... 12 minutes
    after
    > >T/O at 3,000'msl, 2500rpms, oil temp unknown due to sender
    malfuctioning
    > >always high. Landed. Oil on dipstick looked thin. Impossible to
    determine
    > >quantity at high temperature. I did not wait for cooling. Added two
    quarts
    > >to the 5qts (I think) already onboard. Ran cooler on the way back
    home at
    > >2300rpms.
    > >
    > >Question: Can you have too much oil pressure?
    >
    > Within reason, its like being too rich or too thin. <G>
    >
    > The down side to "too much" oil pressure is that if you have a can type
    > filter you can blow the gasket out or fail the crimped seal on the
    filter
    > housing and blow out all the oil in a few seconds. You might also
    damage
    > the sealant between the case halves if your engine case hasn't been
    > modified to provide a separation between the forward and center cam
    > journals and the outside of the case.
    >
    > Cessna worked with Lycoming to RAISE the oil pressure on the current
    > production planes. They changed the red line on the gauge and they
    picked
    > up the pressure at a different point on the engine where the
    pressure is
    > known to be less than at the pump outlet, which is where the older
    > Lycoming's picked the pressure tap.
    >
    > The end result is that if you measured the OP on a new C-172 at the old
    > location where your Musketeer is taking its pressure reading, that
    the red
    > line for the new Cessna is about 125 PSI, or ~25# higher than the older
    > plane's gauges read it.
    >
    > For those that want a more in depth discussion, I refer you to this
    article:
    >
    > http://egaa.home.mindspring.com/new.htm
    >
    > Bob Steward, A&P IA
    > Birmingham, AL
    >







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