Forum Discussion

Tom_Barb's avatar
Tom_Barb
Explorer
Oct 13, 2017

Fuel caps

We were required to replace our 150 gallon fuel tank due to a crack resulting from the tank flexing as the pressure in the tank varying, as the fuel is used the space of that fuel must be replaced by air. the new fuel tank caps require a vacuum pressure to be created prior to the cap to allow any air to enter.
This is mandated by EPA so as to not allow fuel vapors to escape to the atmosphere.
As it turns out this pressure is too great for the large tanks, and will cause the tank to flex way too much.

be aware buy the proper caps.
Class A
  • path1's avatar
    path1
    Explorer
    Oct 13, 2017
    Subscribed...Sounds like they are making you upgrade to current standards. My 2001 Cummins 5.9 came stock with a vent on top of tank. I don't see why you would have to "upgrade" to a newer standard with the fuel system built by OEM in 2000.
  • Tom_Barb's avatar
    Tom_Barb
    Explorer
    Oct 13, 2017
    path1 wrote:
    Subscribed...Sounds like they are making you upgrade to current standards. My 2001 Cummins 5.9 came stock with a vent on top of tank. I don't see why you would have to "upgrade" to a newer standard with the fuel system built by OEM in 2000.


    All you can buy now are the pressure vented caps?
  • K_Charles's avatar
    K_Charles
    Explorer
    Oct 13, 2017
    The vented cap should only be 2 PSI and 2" of vacuum.
    The non vented cap is the one you don't want.
    You can still buy them both.
  • wa8yxm's avatar
    wa8yxm
    Explorer III
    Oct 13, 2017
    You may need to shop a vintage parts store but try the big suppliers like Witney (JC Witney) in Chicago or on line.. I mean you can still get Model T parts from them .
  • Tom_Barb's avatar
    Tom_Barb
    Explorer
    Oct 13, 2017
    wa8yxm wrote:
    You may need to shop a vintage parts store but try the big suppliers like Witney (JC Witney) in Chicago or on line.. I mean you can still get Model T parts from them .


    This is a great idea.

    2 pounds pressure in a 150 gallon tank would be a working force of 14,768 pounds. With 2 HQ of Vacuum, the same is applied in reverse. work this tank that much over 18 years and you've got a problem.
  • SidecarFlip's avatar
    SidecarFlip
    Explorer III
    Oct 13, 2017
    jplante4 wrote:




    Good non explaination answer but I'd use a smaller drill bit.
  • path1's avatar
    path1
    Explorer
    Oct 13, 2017
    I've got one of these (link below) laying in my carport right now. You can have it if it will fit your fuel filler hose size, I'm near SeaTac. Best results the nipple gets a chunk of hose, then a pre 1970 VW bug fuel filter to keep out dirt, which is better than OEM, which is a nipple sticking out on top of fuel module.

    Awhile ago on the Cummins web site, a guy spent lots of $$$ for a venting problem. Turned out his "vented" fuel cap was no longer venting because of dust/dirt in fuel cap mechanism.

    http://cppdiesel.com/fass-rm1001-return-line-t-universal/

    If your going to drill any holes, get a "stant" brand locking fuel cap. The type that has a cover tab for the keyway. Drill out the keyway slot that is under the tab and all the way through other side. The tab works as cover for the newly drilled "vent".

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