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Thread: High Oil Pressure

  1. #1

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    High Oil Pressure

    My O-320 has always had oil pressure over 80 psi even on a warm day. Lately, it's up around 95 and I'm starting to worry about blowing the oil cooler.
    ALL the washers have been removed from the (old style) relief valve. Cylinder and oil temps are good.
    Suggestions?
    Question: Is the newer-style relief valve a direct replacement for the old one?

  2. #2

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    It's probably the prop seals ect you more have to worry about. Give Mark at Airparts in Winnipeg a call, they stock a lot of new but without the cert's parts. Great for us exp guys as they are a fraction of the price.
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  3. #3
    www.SkupTech.com mike mcs repair's Avatar
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    Not knowing they layout of your system.... maybe a flap of rubber in the end of a hose where the end screws on??? Just a wild guess....


    Sent from my iPhone using SuperCub.Org

  4. #4
    skywagon8a's Avatar
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    Does your oil pressure gauge needle go to zero when the engine is shut down? If it only goes down to 5 or 10 psi, it's your gauge.
    The maximum allowable pressure is 115 psi.
    This may be informative for you: https://www.cessnaflyer.org/maintena...-pressure.html
    When you removed the washers, did the oil pressure go down at all?
    N1PA

  5. #5

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    Gauge,

  6. #6

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    The gauge goes right down to the pin (below the zero mark).
    Going from four or five washers to none didn't significantly reduce the indicated pressure.
    Thanks NDRII thanked for this post

  7. #7
    skywagon8a's Avatar
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    See that hole at about 6:30? Is there any blockage over or in it? Can you blow compressed air through it? That is the drain of excess oil back to the sump.

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    Do you have another spring which is shorter than the one in there now? If so put it in, start the engine and notice what the oil pressure does. If it doesn't come up at all of course shut it down. If it makes no difference, then try removing the spring all together and try again. If there is still no difference then the drain is blocked somehow and a replacement relief valve assembly will do nothing for the situation.

    Increasing oil pressure is usually not an issue. Normally one gets worried when the pressure goes down. The only time that I've seen high oil pressure in a Lycoming was in an Enstrom helicopter during cold weather start up. Then it was just a matter of letting the oil warm up a bit until the pressure came down.

    What are you using for oil? You didn't happen to put in some W120 or SAE 60? That could do it.

    Another thing you could check is with the valve removed as in the picture, pull the prop through by hand or crank with the starter. Does oil flow out of that center hole? If not there is some internal blockage somewhere.
    Last edited by skywagon8a; 07-21-2019 at 12:11 PM.
    N1PA
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  8. #8

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    Good suggestions. Thanks Pete.
    I'm using Shell 15W50.
    Larry
    Thanks C130jake thanked for this post

  9. #9

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    Larry,
    i just went thru a similar experience.
    Had the pressure reg off twice, fooling with washers, scrutinizing seat and ball,
    changed oil, inspected filter, scratched my head, a bunch of times, lost a bit of sleep.
    Turns out it was the (relatively new) gauge that was giving erroneous reading.
    In my case, adding power beyond 2400 rpm, resulted in a corresponding drop in oil pressure, more power less pressure.
    Still haven’t figured the logic behind that but different gauge solved the problem.

    Symptoms you are describing are typical of a failing Bourden tube type gauge.
    Hopefully a simple fix, good luck with it.
    Doug
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  10. #10
    Seaworthy's Avatar
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    Quote Originally Posted by skywagon8a View Post
    See that hole at about 6:30? Is there any blockage over or in it? Can you blow compressed air through it? That is the drain of excess oil back to the sump.

    Name:  0917_IMG_4397.jpg
Views: 427
Size:  21.3 KB

    Do you have another spring which is shorter than the one in there now? If so put it in, start the engine and notice what the oil pressure does. If it doesn't come up at all of course shut it down. If it makes no difference, then try removing the spring all together and try again. If there is still no difference then the drain is blocked somehow and a replacement relief valve assembly will do nothing for the situation.

    Increasing oil pressure is usually not an issue. Normally one gets worried when the pressure goes down. The only time that I've seen high oil pressure in a Lycoming was in an Enstrom helicopter during cold weather start up. Then it was just a matter of letting the oil warm up a bit until the pressure came down.

    What are you using for oil? You didn't happen to put in some W120 or SAE 60? That could do it.

    Another thing you could check is with the valve removed as in the picture, pull the prop through by hand or crank with the starter. Does oil flow out of that center hole? If not there is some internal blockage somewhere.
    Pete--I have kinda the same issue-- If I keep just a hair less that 6 quarts in the crankcase the pressure remains in green-- excepting to T/O and climb power. I have approx. 860 hrs since TBO and my engine pushes/ burns zero oil as long as I keep it at six. Still--- the high oil pressure always nags at me. I have 15 years on all of my hoses and thinking about changing them all out this year at annual. Pete Connor doesn't think the elevated pressure is a concern-------but-----. Feel like taking a look?
    Marine Corps Aviation since 1966

  11. #11

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    KThe amount of oil in engine sump has no effect on oil pressure, (unless it’s empty)
    Temperature (warmer = thinner oil = less apparent pressure), and engine rpm (speeding up engine driven oil pump = more pressure)
    When max desired oil pressure is reached, say 85 psi, regardless of oil temp or engine rpm, the oil pressure relief valve comes into play and will bypass excess pressure as it was adjusted to do following engine manufacture or overhaul.
    With the Lyc pressure relief system it’s very unusual to see pressure increase over time. I think Pete pointed out about the only scenario where this could happen, and I would venture to guess that if you have a clogged 1/4” oil gallery you’ve got more serious issues (where did that debris come from?)
    There are several scenarios that could lead to LOWER than desired oil pressure at cruise setting, some serious, some not so serious and easy to remedy.
    All trouble shooting should begin with confirming accuracy of your gauge.

    I just dealt with a situation where mechanical oil pressure gauge indicated DECREASE with increased rpm at normal operating temp. Oil pump cavitation?
    Oil pickup drawing air? Nope. fortunately in this case
    turned out to be a faulty gauge, I can only guess airframe vibration was affecting gauge function (!?)

    Hope this speel helps a bit.

    doug
    Last edited by Oliver; 07-22-2019 at 08:08 PM.

  12. #12

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    EAA video on Lyc oil pressure adjustment:

    https://www.eaa.org/Videos/Hints-for.../1687375685001
    Last edited by Oliver; 07-22-2019 at 08:04 PM.

  13. #13
    skywagon8a's Avatar
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    Quote Originally Posted by Seaworthy View Post
    Pete--I have kinda the same issue-- If I keep just a hair less that 6 quarts in the crankcase the pressure remains in green-- excepting to T/O and climb power. I have approx. 860 hrs since TBO and my engine pushes/ burns zero oil as long as I keep it at six. Still--- the high oil pressure always nags at me. I have 15 years on all of my hoses and thinking about changing them all out this year at annual. Pete Connor doesn't think the elevated pressure is a concern-------but-----. Feel like taking a look?
    I'm inclined to agree with Pete, however let's look at it to be certain. Call me.
    N1PA

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