Late 379 Cat fuel line questions

Discussion in 'Peterbilt Forum' started by w9l, Jul 31, 2020.

  1. w9l

    w9l Light Load Member

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    Oct 12, 2013
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    04 build 05 379 exhd with acert plumbing questions.

    While under the truck today clearing the condensation drain tube for bunk ac I noticed damp dust around the fuel fittings going into an affair that is some kind of splitter for supply and return fuel in the middle of frame between tanks. Can someone explain the function of this junction and the directions of flow here. I tighten the brass fittings after loosening the flare nuts on two of them that were hardly more than finger tight. Tracing hoses I think they were the top draw connections. I am familiar with both top and bottom draw setups with a gravity crossover line. My KW pulls from and returns to the pass side tank (low side of the road) and just crosses over from drivers side. Has shutoffs on crossover at each tank. When I used to give a flip about what I weighed I would sometimes run pretty low fuel. I could ease of the shoulder a bit and let fuel cross to pass side tank and then shut valves off on crossover if I got stupid and cut it too close. 379 has shutoffs on hose coming out of bottom of both tanks but those hoses go up to the junction I mentioned. So how does this all work? Was sucking air at those fittings. Think I am gonna replace all the fuel lines as the dust collected on them is sorta damp like the may be leaching?
     
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  3. spsauerland

    spsauerland Road Train Member

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    Is valve your talking about for the return hoses? Peterbilt used a valve by GT development that was supposed to equalize both tanks fuel levels.
     
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  4. w9l

    w9l Light Load Member

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    It appears to be for both pick up and return lines. It is the junction of 6 stratoflex hoses. Not positive on the sizes but I think they are #8 and #10. If that is correct then it is as follows:
    One #10 on a brass jic/npt 90*elbow out of the middle of block running forward to engine. In the same plane there are two #10 hoses plumbed to seperate ports, one on either side of middle port that goes to engine bay. The hoses both run to the bottom of the fuel tank on their respective sides.
    When laying under truck looking up at block there are three more ports directly below the ones previously described. They are all the smaller size with one going forward to engine and the other two from each side of the block to the top of the fuel tank on there respective sides.
     
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  5. w9l

    w9l Light Load Member

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    I haven't traced lines inside engine bay but I am thinking the lines out of bottom are to some way equalize tanks and the other lines are likely draw lines.? I think, no, I know I am having issues with air in fuel . Have seapage of fuel at this block
    Thinking related.
    Was told to replace block with 2 brass T's. Not sure that is a very good plan...
     
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  6. WREN

    WREN Medium Load Member

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    IIRC its just a junction for the return and equalization of the tanks like you said. The problem with the T idea again IIRC is that the return lines have check valves in that junction to create a specific amount of back pressure.
     
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  7. Bernard D

    Bernard D Bobtail Member

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    Jun 27, 2020
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    Its your fuel tranfer fitting .
    Replace since your on it..it transfer fuel from one tank to the outher .
     
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  8. w9l

    w9l Light Load Member

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    Ok, so this evening I am replacing lines from tanks to the splitter and the t fitting on middle of crossmember at front of tanks. I unhook a #8 jic hose connected to brass elbows with 3/8 or 1/2 NPT Male screwed in top of DS tank. It wasn't even finger tight. I thought there should be a draw tube here somewhere but it is not under that connection. Has #10 hose with shutoff connected to the bottom of each tank and run up to what I think is just a big t with large line running forward to engine bay. Has this been converted to a bottom draw?
     
  9. lester

    lester Road Train Member

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    Yes bottom draw. Some are setup that way
     
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