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Detroit 6V92 fuel leak

Discussion in 'Technical Discussion' started by Ben T, Dec 31, 2018.

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  1. Ben T

    Ben T New Member

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    After the boat sits for a couple of days the port engine is hard to start. Just wondering if anyone would know where there is a check valve on a 1986 500 Chris Craft that maybe leaking off
  2. Capt Ralph

    Capt Ralph Senior Member

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    Before we try to read your mind, What engines do you have? Tune and rig?
  3. Ben T

    Ben T New Member

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    They are 6V92’s.
  4. Capt Ralph

    Capt Ralph Senior Member

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    There usually would not be a check valve for Detroits. You have a leak some where.
    When the port engine does start, do you smell un-burned fuel and a bit more white smoke?
  5. Ben T

    Ben T New Member

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    No I don’t. We just had the injectors replaced and didn’t see a fuel leak anywhere. The motors do sit higher in the boat than the tanks do that’s what made think there would be a check valve to fuel from leaking back to the tank
  6. Capt Ralph

    Capt Ralph Senior Member

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    Did this problem start after the injectors were replaced?

    Leaks can be internal, a dripping injector. Common when all are just replaced.

    An injector tube leaking inside the engine. Common when re-using the same tubes after injector service.

    An air leak into the pre filters as fuel drains away.
  7. Capt Ralph

    Capt Ralph Senior Member

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    Also, How fresh are the motors? This problem get worse as the weather got colder?
    Do you have block heaters?
    Engine turns over at great speed from the starter?
  8. d_meister

    d_meister Member

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    I've had the same problem on two different boats, both of them having a fuel tank level physically below the height of the primary Racor filters. One was a Cummins engine, and the other was a Northern Lights generator. The fix for both was to replace both upper "O" rings on the Racors. The previous operator didn't change the "O" rings when replacing filters because they "looked good". The engines would start easily and run fine after having been run within hours or a day, but would require a lot of cranking to get them going after days of non-operation.
  9. captholli

    captholli Senior Member

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    If you have Racor filters fitted than there will be a check valve on them in the form of a seated ball bearing type check valve. I've had two seperate occasions where the ball o-ring seat had deteriorated from being old and another time where microbe slime had built up on the check orifice allowing fuel to return to the day tank. Racor sells a rebuild kit with all the needed O-rings, check ball and seals for all of their products.
  10. Pascal

    Pascal Senior Member

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    I doubt an injector or tube would cause this issue as fuel would still be right there.

    Your problem is likely a very small leak on the suction side incl the racor. I had this problem years ago on an 8V71. Too small to cause a problem while running but just enough to let air in and fuel go back to the tank

    Try turning off the fuel selection valve to see if it makes a difference
  11. captholli

    captholli Senior Member

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    Isolate or valve off the inlet side of your Racor as Pascal recommended and see if your problem is eliminated. If so its either the flat lid ring seals or T handle O-ring per post #9 or your internal Racor check valve. The rebuild is a simple job but it can be messy.

    ffgvc.png
  12. Capt Ralph

    Capt Ralph Senior Member

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    It happens. That's why I asked what color the exhaust was when it did start. Also, does the sump oil smell of fuel.
    New injectors off the shelf is not a good move with out popping, matching and bench testing all before install.
    Last edited: Jan 2, 2019
  13. Capt Ralph

    Capt Ralph Senior Member

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    The Racor air leak that a few are talking about is common.
    As you originally asked, the only Check Valve is in the Racor.
    If your return tube is low in the tank, This should not be an issue.
    If your return to the tank dribbles in at the tank top, this may be an issue.
  14. cleanslate

    cleanslate Member

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    I would first drain the Racor unit, then disassemble it clean out with fresh diesel get all the dirt and stuff with in the unit out , including the steel ball ,etc. like in the picture above. Make sure you put everthing back together as it came apart! Take a photo or two before and during the disassemble to refer to if you need. And install all new O-rings and gaskets.
    While the Racor is apart or before it's apart shut off the fuel ball valve before the filter to stop the flow of fuel. You should have a natural flow of fuel coming from your tank to the Racor . Your engine height doesn't mean a thing, fuel should be freely flowing to the Racor.

    If it's not flowing your fuel line is plugged up a little or a lot with tank skank. You may have to blow some air with a small compressor back into the tank through the fuel line from the ball valve back to the tank, to remove the blockage. One or two puffs of air through the fuel line and listen for the air bubbles in the tank to make sure you are through and clear.
    Now fuel should come out of the line freely.
    I would recommend you get the tank cleaned/fuel polished too if you find the line was plugged up.

    See if that doesn't help with your starting problems. I'm not aware of fuel every flowing back to the tanks on boats like yours and mine. When you change the Racor filter it should refill with fuel on it's own from the tank .
  15. Ben T

    Ben T New Member

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    That’s is exactly what the one engine is doing and they have rancor filters
  16. cleanslate

    cleanslate Member

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    Before you start the problem engine, pop off the Racor top and see if there is an air gap with in the housing . Fuel should be up to the top when you open it up. If not that's a problem, it could be the top O-ring or Cover plate gasket it's self as mentioned by others, causing this.
  17. Capt Ralph

    Capt Ralph Senior Member

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    Curiosity; Why were the injectors replaced?
  18. Ben T

    Ben T New Member

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    We had a bad smoking issue on the port engine and replaced them. It has seemed to fix it.
  19. Ben T

    Ben T New Member

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    Here is a pictures of the filters that are on our boat

    Attached Files:

  20. captholli

    captholli Senior Member

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    I'm assuming the butyl O-rings on the T handles are spares when changing elements or were they forgot when reassembly took place? If so they're now stretched beyond the threaded stud size and will be a sloppy fit.

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