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Thread: Got a head scratcher here... any ideas?

  1. #1
    efrench's Avatar
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    Default Got a head scratcher here... any ideas?

    I have suddenly developed an oil leak that is quite perplexing. This first appeared during a longer XC flight and now is persistent. I noticed the leak while unloading from the trip and discovered oil on the fuel step and belly. Further investigation I found a bit of oil in the lower cowl, on top of the air box, more on the left than on the right, however it appears to be blown up to the nose bowl. The oil will drip from the air dam on the lower cowl after landing.

    I have an O-320 (no suffix; narrow deck) with 400 hours SMOH (and a fine OH it was). Prior to this event, the motor would not use any oil during the first 20 hours of a change and then would use 1 qt during the next 5. I have changed the oil at 25 hour intervals and the filter at 50.

    I checked all of the obvious possibilities, i.e. Oil filter, fittings and front seal. No indication of any leaks at all, and the pulley in front of the front seal is as dry as can be. No oil on the windshield or prop. I did find the oil filler tube loose, so I replace the gasket and tightened to no avail. Also found the rocker cover screws to be 1/4 to 1/2 turn loose. Again tightened but still leaking. No indication that the pushrod shroud seals are leaking. No oiled or wet areas on the motor or accessories.

    It is true that a little oil goes a long way and I may be loosing a quart in 5-10 hours. So, what else can I check?

    Thanks
    "If you do something; something else will happen. Don't wiggle the controls" Jim Alsip; EAA Webinar Oct 2015

  2. #2

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    Default Re: Got a head scratcher here... any ideas?

    Ed, had this happen to me 2 times. Both were the old oil cooler . Tiny pinhole from rubbing on the bottom if the cooler shroud sometime in the past. Couldn't find it until she really let go over tyonek.
    Fly safe fly low fly slow

  3. #3
    efrench's Avatar
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    Default Re: Got a head scratcher here... any ideas?

    Quote Originally Posted by eskflyer View Post
    Ed, had this happen to me 2 times. Both were the old oil cooler . Tiny pinhole from rubbing on the bottom if the cooler shroud sometime in the past. Couldn't find it until she really let go over tyonek.
    Thanks. Ill check that. My cooler is a newer Niagra, rear baffle mount. Definitely easy to inspect.
    "If you do something; something else will happen. Don't wiggle the controls" Jim Alsip; EAA Webinar Oct 2015

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    Default Re: Got a head scratcher here... any ideas?

    the other thing to check is your breather tube. I have had oil fly into the cowling from it also. I would almost rule out your oil cooler if it is a rear mount niagra. Good luck, if you don't find it by this next Thursday I will be home and can help ya with some dye to put in the oil and we can wash the engine down then go fly it and look with a black light and try and find where it is coming from. I have had excellent success with doing this.
    Fly safe fly low fly slow

  5. #5
    efrench's Avatar
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    Default Re: Got a head scratcher here... any ideas?

    That sounds great. Thanks
    "If you do something; something else will happen. Don't wiggle the controls" Jim Alsip; EAA Webinar Oct 2015

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    Dwain's Avatar
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    Default Re: Got a head scratcher here... any ideas?

    +1 on the breather tube. I was losing about 1 qt. in 2 hrs. No oil anywhere. Read something on this forum about the position of the breather tube and checked mine. Sure enough it was apparently sticking down far enough to miss the belly. Moved it up, but a little too much and ended up with oil in the cowling. One more adjustment and I was good. Luck - Dwain

  7. #7
    smcnutt's Avatar
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    Default Re: Got a head scratcher here... any ideas?

    Wet or dry vacuum pump? We had an issue where we thought we had oil coming out of the engine breather tube. Did all sorts of things to fix that but still had oil getting all over. Finally I wire-tied a coke can on the breather tube to confirm that is where it was coming from. Turns out it was actually the wet vacuum pump vent line that was a foot away.

    Once the oil hits the airflow it can look like it's coming from anywhere. Good luck.
    “Common sense is in spite of, not the result of, education.”
    ― Victor Hugo

  8. #8
    Gilbert Pierce's Avatar
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    Default Re: Got a head scratcher here... any ideas?

    I had a prop seal leak. Pulley and flywheel both dry. Bottom and top of engine front case oily and drips off starter.

  9. #9
    Pacerfgoe's Avatar
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    Default Re: Got a head scratcher here... any ideas?

    I would also check for a cracked cylinder head, look closely around the spark plugs for any sign of oil or cracks. I don't think 320's are prone to this but you can also look for a crack at the cylinder head to barrel area.
    I found cracks around my plugs once when signs of oil leaks appeared.

    New cylinders at overhaul or did you go with overhauled cylinders?
    Good Judgement comes from Experience --and Experience- well, that comes from Poor Judgement

  10. #10
    Homer Landreth's Avatar
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    Default Re: Got a head scratcher here... any ideas?

    Quote Originally Posted by Gilbert Pierce View Post
    I had a prop seal leak. Pulley and flywheel both dry. Bottom and top of engine front case oily and drips off starter.
    +1 with Gilbert on the prop seal. I had the same issue fixed with a new prop seal. In flight the area proximity with the prop seal is pretty self cleaning from airflow. Any small leakage is just propelled off and backwards into the cowling area. and pools there.

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