Cummins ISX CM870 Black diesel fuel and clogging fuel filter

Discussion in 'Volvo Forum' started by Adamali21, May 25, 2026 at 12:26 AM.

  1. May 25, 2026 at 12:26 AM #1
    Adamali21

    Adamali21 Light Load Member

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    Jul 24, 2018
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    Hello everyone

    My dads 2007 Volvo VNL 780 with a Cummins ISX CM870 has been giving him a hard time with clogging of his fuel filter, he has been getting black oily diesel fuel, I opened the fuel filter and it looks like oil, at first we changed out the injector seals but still getting black diesel and clogged fuel filters, then we changed out the fuel pump and that didn’t help we check all the fuel lines and they are good, so we still haven’t found the issue has anyone experienced this type of issue before. Thank you in advance
     
    Adamali21, May 25, 2026 at 12:26 AM
    Adamali21, May 25, 2026 at 12:26 AM
    #1
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  3. May 25, 2026 at 3:51 AM #2
    Magoo1968

    Magoo1968 Road Train Member

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    Mar 18, 2021
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    Are you sure it’s not algae? If so there’s products to treat it . If I’m not mistaken you feel the fuel and if it slippery it’s algae and if it feels course it combustion getting into the fuel . Look up old threads that used to be big problem when bio diesel first came out..
     
    Magoo1968, May 25, 2026 at 3:51 AM
    Magoo1968, May 25, 2026 at 3:51 AM
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    IH Truck Guy Thanks this.
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