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Thread: Oil Pressure Problems

  1. #1

    Join Date
    Nov 2011

    Oil Pressure Problems

    Good Morning Fellow Flyers and Gear Heads.

    A week ago last Friday, I flew out to KC area to visit an ailing Uncle (2 hour flight each way).
    Had a great day for flying and it had been some time since I had taken a true cross country.
    All went as planned and the old Skyhawk never had a burp.
    The next day I flew my wife up out to lunch. (less than 1 hour each way )
    We had a rough ride home no matter altitude chosen.
    Still no burps from the reliable old 0-360 A4M.
    Last Wednesday morning I flew up to work. Beautiful moon lit morning with light winds.
    About 2/3 way up, my oil pressure had dropped from the usual 90 PSI to an alarming 40 PSI!!
    With my attention now peaked out on the oil pressure gage, and blood pressure with higher numbers, I decided to continue to my work destination where I would at least have a hanger and tools to do some diagnosis.
    On the ground at idle the gage was only reading about 10 PSI!!! (Oil Temps never wavered from normal thru it all)
    After my 8 hour shift, I went out and checked the oil and the regular preflight and couldn't find anything out of the ordinary.
    Boarded and fired up only to see the oil pressure to come up to its regular numbers???
    Since it is only a 38 nm flight home, I decided to make the trip home, watching the oil pressure gage all too often, if that is possible.
    Again, about 2/3 back, pressure slipped down to 65 PSI. (oil temps again normal) Still alarming but not yet an emergency situation, I trudged on home.
    This time at idle on the runway the gage was reading 20ish, better but still not good!
    Once in the hangar I drained the oil and pulled the suction screen in the oil sump. There I found an unusual amount of light colored, non-metallic material. No Steel, cast Iron, or Aluminum??
    I washed up the sample and after letting it dry, put it in a small glass jar.
    Next I pulled and inspected the oil filter. Little or no metals and more carbon like stuff than usual? Stuff but not enough to tear things apart and go looking for trouble. After last years with the IO-320 rebuild I was not too anxious to tear another one down this summer.
    I dried out the filter contents and put them in a sealed container.
    Friday I drove up to a local Engine rebuild shop with my samples in hand and a document I had complied of all the time-in service for all the major components in the engine.
    The engine Guru at the shop looked very carefully at my samples, listened to my story, and told me that he saw nothing alarming in my samples except that the screen contents seemed strangely large sized chunks of carbon. HMMMM.
    He suggested I go back home and remove the oil pressure control valve to see if there was one of the particles preventing the ball from seating. With the seat not closed, cold oil would be thick enough to provide pressure but as it heated up to running temp it would thin out to a point that much pressure would be lost back to the sump if the ball was off the seat any distance at all.
    Relieved that it might not be a major tear down, I headed back home to check out the valve. After carefully cleaning any loose debris from around the valve housing, and placing clean towels under the opening, I carefully removed the housing.
    There laid the ball with a little chunk of carbon stuck to it!!!!!!
    After carefully cleaning all parts I reassembled the valve and installed it back on the engine and safetyed it in place.
    Fresh oil, new filter installed, cowl back on and secured, it was time for a test flight.
    With a plan to stay within a mile of my strip and get a reasonable altitude I started up. Normal idle oil pressure at start-up, I taxied out to take off. At Run-up, all systems normal, pressure up to the normal 85+ at 1700 RPM, I launched on a planned one hour adventure. I'm sure the neighbors all thought I was crazy as I circled the area at a set altitude and just went round and round and round. Everything remained at normal readings after an hour of circuits and now the test at idle on the ground. Pressure remained above 70 taxing in!!! Problem solved!!! BIG RELIEF!
    Now.........Why the larger than normal chunks of carbon?
    As near as I can tell, my normal flying back and forth to work and local jaunts to bore holes in the sky and kill my share of the pesky bugs, I seldom run at high power settings nor am I usually in the air for more than an hour at a time. Temps usually come up to good drying numbers to cook out the moisture in the engine. But, sustained flight as in a cross country of 2 or more hours and or 4+ hours of hard high altitude cruising will, as we used to say in our hot rods, "blow the cobs out of the engine"
    I think the carbon was dislodged during the KC trip and consequent lunch trip and was deposited in the oil where it managed to get to the pressure control valve and scare the begeezous out of me on a dark cold morning on my way to work.
    After 4000 hours in the air, one can get a false sense of well-being and ultimate safety, especially if most of that time was flown in the same old faithful stead.
    I now have a better scan of the panel in flight and start-up and shutdown than in the recent past. LESSON LEARNED!
    I will also try to get out on cross countries more often and keep things loose and clean in the trusty old engine.
    For the next few oil changes I will also cut the regular interval from 50 hours to 25-30 to make sure things are not happening inside that will cause more surprizes.

    In conclusion (finally), not all things that go bump in the night can be deadly nor expensive, BUT, they sure can make you think a little more about what you are doing and the risks involved.
    Bob Doughty
    EAA 569472

  2. #2
    Is the O-360 A4M subject to AD 96-09-10 (oil pump)? If so, have you complied with AD? When changing the oil pump, there is a Lycoming Service Instruction #1341 which drills a hole in the accessory case to improve lubrication to the oil pump impeller idler shaft. Sounds like the non-metallic light colored material might be the aluminum body of your oil pump. What are the operating limits on your engine? I believe 10 psi at idle in a Lycoming is below the red line. My O-290D with a new oil pump and around 1560 hrs TT has about 80 psi @2300, and 50 psi at idle. The other thing the light colored material could be is bearing material. I would consider a teardown due to running at that low oil pressure at idle, or at least oil change/oil analysis every 25 hrs? Did you mention how many hours since overhaul are on the engine? Just my two cents. Good luck.
    -Joel Marketello

  3. #3

    Join Date
    Oct 2011
    New Hampshire
    That problem is not really uncommon. Lyco's are actually OK to run gently at lower oil pressures and folks who have the problem described run them VERY gently for the short time that it takes to get to the airport. My personal experience with the exact same issue is that it is very unlikely that any harm has been done to the engine and you do not need to over react.

    Lycomings do well when run hard. Attempting to baby the engine is often false economy as you get lead buildup in valve guides and stuff like carbon in places that have gone from hot to cold to hot etc. So then you take the engine out and run it the way it was designed to run and the crap starts to get flushed out.

    From the description of the type of flying that this engine does, it will likely age out well before the published TBO. It needs to fly harder, not have its innards disturbed.

    Best of luck,


  4. #4

    Join Date
    Nov 2011
    AD complied with in 1991. Hardened metal impellers and shaft are in this engine.
    None of the material in the screen or filter are Metalic.
    NOT aluminum.
    Put a .060 chunck of anything under the oil pressure control valve ball and let the oil warm up to operating temp. >180*
    The spring side of the valve dumps directly to the sump.
    My pressures are now 75-80 at idle and 90 at 2500.
    Thanks for your two cents.

  5. #5

    Join Date
    Nov 2011
    Totally agree Wes.
    Too many jump directly to un needed and very expensive tear downs.
    Troubleshooting and proper diagnosis, including help form Experianced Engine rebuilders can save a lot of time, money, and grief.
    The O-360 A4M is a bullitproof engine with a great reputation for durability and long life.
    Thanks for your input.


  6. #6

    Join Date
    Oct 2011
    My Honda Civic had a flickkering oil pressure warning light. I checked the oil pressure with a mechanics oil pressure gauge and found it at 2.5 psi. (at any rpm).
    The problem was a chip of aluminum under the relief seat. With that chip removed, it now has the normal 70 psi.

    Took all day to get to the relief valve. Too bad it can't be cleaned somehow without disassembly.

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