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Thread: need help locating fuel leak at tank

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    speybro's Avatar

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    need help locating fuel leak at tank

    I just bought an o9 6.7 2500. Had it checked out and fixed several maintenance issues. However, we just filled the tank and noticed after driving a fuel leak from on top of the tank at a steady drop per second rate. The leak comes from the top of the tank. After a few minutes the leak quits. I suspect the return line to the tank because that is under pressure but I guess it could be a leak in the tank itself. I am getting ready to put the twin filter (2u Donaldson, and water separator) under the driver's seat and above the cross member and would like to know if anyone else has had this problem. I have crud catching filters on my other Cummins trucks and I know they have saved me injector woes. Do I need to pull the tank to find this leak, and at the same time maybe install a Fass pump? Thank you in advance


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    Old... But Still Here! AnOldBiker's Avatar

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    I'm not a mechanic, but I would suggest looking at the top of the tank through the wheel well. On my '06 I can see the top of the lift pump that way. You should have sight of both the return and the suction quick disconnects. If they are leaking, while the truck is running, it should be noticable or the top of the pump would be wet with fuel. There are two roll over vents on top of the tank, one front and one rear. I had a leak once, but found it was the front vent seal had gone bad and when I replaced both vent seals, it stopped. If this is a stock set up, I can't think of any other way it would leak outside of a hole in the tank (pray not) or a leak from one of the fuel lines. Maybe someone else can chime in.


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    Permanent Vacation K-Sons's Avatar

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    I wold do like anoldbiker said maybe one of the fuel disconnects is leaking one of the O rings may have gone bad


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    Cerberus4877's Avatar

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    I have found it to be easier to remove the bed verses dropping the tank..... In My Humble Opinion get see a bit more and don't have to drain the tank


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    speybro's Avatar

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    Thank you for the clues


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    Old & Grumpy! Polaraco's Avatar

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    Quote Originally Posted by AnOldBiker View Post
    I'm not a mechanic, but I would suggest looking at the top of the tank through the wheel well. On my '06 I can see the top of the lift pump that way. You should have sight of both the return and the suction quick disconnects. If they are leaking, while the truck is running, it should be noticable or the top of the pump would be wet with fuel. There are two roll over vents on top of the tank, one front and one rear. I had a leak once, but found it was the front vent seal had gone bad and when I replaced both vent seals, it stopped. If this is a stock set up, I can't think of any other way it would leak outside of a hole in the tank (pray not) or a leak from one of the fuel lines. Maybe someone else can chime in.
    Good answer.

    The fill tube could leak at the rubber coupler when the tank is filled to the top too.


    2003- 3500 RWD Automatic.
    S & B intake, BD Intercooler, Pusher Air Horn, MM3 Double R Tuning, Turbo Timer, electric Flex-a-lite fans, FASS 95,
    50 HP tips, upgrade to 351 turbo, 3.42 gears, Twin air compressors, air bags, Remote dual oil filters, Hellwig sway bar, Front Winch. Home made Fuel Heater, BD Exhaust brake with Torque Lock. Tons of TLC

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