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  1. #1
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    Pro XS Fuel Leak Help

    Serial #: 1B555160

    I’ve got what I believe to be a fuel leak based on the slick on the water and the smell. Could be oil, but I think it’s fuel. The attached picture is right after initial start up and idling to the dock. I took the top cowling off while on the water and couldn’t see any leaks anywhere, but I’m honestly not sure I was even looking in the correct spot. The motor seemed to run fine on the few short runs I made and the slick on the water was much less visible as the day progressed but that could just be from the lighting being different and not reflecting the same way.

    Can anyone give me a starting point on where to look? I plan to get muffs Or fill a trash can with water to run the motor at home for troubleshooting.

    A711FA13-81AF-4BED-A71F-B8DDB3881D1A.jpeg

  2. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
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    #2
    Check the fuel line, primer bulb, and make sure that the VST isn't overflowing into the vent hose (which dumps into the lower chaps, below the adapter plate, running down the STB side of the engine). That last one is a possible candidate as most any other leak would affect how the engine idled.

    I would not run the engine again until located and corrected (FIRE and EXPLOSION hazard).


    Dual Mercury Master Technician- for Mercury Outboards, Mercruiser and Mercury Racing at European Marine in Greenville, SC.
    Still consider myself a "Marine Apprentice" after 47 years (learn something new every day).
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  3. Member
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    #3
    Quote Originally Posted by EuropeanAM View Post
    Check the fuel line, primer bulb, and make sure that the VST isn't overflowing into the vent hose (which dumps into the lower chaps, below the adapter plate, running down the STB side of the engine). That last one is a possible candidate as most any other leak would affect how the engine idled.

    I would not run the engine again until located and corrected (FIRE and EXPLOSION hazard).
    Thanks Don. I appreciate the help. I’ve got a couple dumb follow up questions:
    1) The VST is fairly large. I’ve always seen it under the cowling but never knew what it was until I googled it after reading your post (that’s how green I am with this stuff). Is there a specific location on it to look for a leak? The top? Bottom? I’m guessing top since you said “overflowing”.
    2) How should I go about finding the leak if I don’t run the motor? Or by run, do you mean just run on a lake but running on muffs to diagnose is ok?

  4. Member lpugh's Avatar
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    #4
    ^^^^^^^^ Also:
    water in fuel sensor, lower front of VST, Look for leaks engine off while pumping the primer bulb firmly
    Thank You Leon Pugh

  5. Member
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    LONGVIEW TEXAS
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    #5
    overflow hose connects to brass fitting on top of vst and loops over the front of plenum remove tie strap and hose at fitting pump bulb , run on hose dont run in lake until leak is found if not found check trim system and gearcase for leaking seals
    .................................................. ...the scariest thing in life is the unknown ...................................

  6. Member
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    Dec 2004
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    Woodland, CA
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    773
    #6
    My water in fuel sensor cracked around the rim and allowed fuel to leak out. It was fairly obvious even without the engine running. Waited weeks for my dealer to get a new one and finally find one myself on Amazon. Installed and everything is fine now.

    NoCAL
    2004TR-21X/2015 250 ProXS
    2B112175

  7. Member
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    #7
    I couldn’t find any leaks while pumping the bulb so I decided to take it to my mechanic. He found a leak where the fuel line goes into the fuel rail. I don’t know how that didn’t cause any performance issues but oh well. It’s fixed now. Thanks everyone for the tips in diagnosing.

  8. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
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    #8
    And thank you for having someone take a look at it, before it became a bigger (or perhaps even a really big) problem.


    Dual Mercury Master Technician- for Mercury Outboards, Mercruiser and Mercury Racing at European Marine in Greenville, SC.
    Still consider myself a "Marine Apprentice" after 47 years (learn something new every day).
    Mercury Parts, Mercury Outboards, Smartcraft & Accessories, Injector Service, TDR Reeds- BBC Sponsor