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  1. #1
    Seaman Apprentice
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    Default pressure test lower unit

    how do they do this test? & where do i find the specs on how much pressure a particular gear case is supposed to hold? i have a radiator pressure tester & could adapt it would that work?

  2. #2
    Rear Admiral rolmops's Avatar
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    Default Re: pressure test lower unit

    This is how I do it.I drain the oil out of the unit and remove it from the the outboard.I attach an airhose with a pressure gauge to the oil inlet of the lower unit and pressurize to about 10 psi.Now i dump the whole thing in a barrel of water and look for air bubbles.You leave it in the water for a few minutes to make sure there are no hidden leaks.And that is it!Do not put more than 10 or maybe 15 pounds of pressure on, because you will blow the seals.
    Make sure the plug is in

  3. #3
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    Default Re: pressure test lower unit

    A good gearcase should still have some pressure after 45 minutes. If not, start looking for leak(s). OMC manuals explain this in detail. There's no need to remove the LU unless you determine there's a leak.
    Jim

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  4. #4
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    Default Re: pressure test lower unit

    How old is your engine, some of the little, or older engines with single seals don't seal all to well. I have run into some gearcases along this line that will a have a groove worn into the drive shaft at the seal, these will hold static pressure, but have some seepage with the engine running.

  5. #5
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    Default Re: pressure test lower unit

    how about if i change the fitting on a radiator tester i have & pump it up to 10 psi. & then wait to see if i have any bleed down? do i have to put it underwater? do i have to drain fluid?

  6. #6
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    Default Re: pressure test lower unit

    When vacuum or pressure testing a LU:1] drain the gear oil (it will mask results otherwise)2] apply vac or pressure (15 psig max)3] wait 30 to 45 minutes, should have some press or vac remaining. No need to put under water unless leakdown fails.4] done
    Jim

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    For basic information on a wide range of topics, see Top Secret File
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  7. #7
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    Default Re: pressure test lower unit

    It's best to pressure test at two different settings according to the factory service manual. First check at 6 psi, then at 15 psi. That way both the orings and the seals are "stressed".

  8. #8
    Seaman Apprentice
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    Default Re: pressure test lower unit

    from 15 psi how much leak down is acceptable over 30 minutes?

  9. #9
    Seaman
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    Default Re: pressure test lower unit

    I had a carb pop-off gauge that happened to fit the fill tube for my lower unit pump. I pumped it up to about 15psi and it appeared to hold for well over an hour. I'm guessing that means my seals are good? Reason I ask is i was sure I had some water in there when I checked at the lake.

  10. #10
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    Default Re: pressure test lower unit

    I rotate the prop shaft and drive shaft, shift the lower unit while it is under pressure. Sometimes moving a shaft will show a leak.

    Silly me, I just noticed how old this thread is, I bet the poster has found his problem by now.
    Last edited by Daviet; August 23rd, 2013 at 10:42 PM.

  11. #11
    Petty Officer 3rd Class
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    Default Re: pressure test lower unit

    Quote Originally Posted by Daviet View Post
    Silly me, I just noticed how old this thread is, I bet the poster has found his problem by now.
    I'd certainly hope so! Lol!
    People should learn how to start new threads, don't you think?

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