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pressure_welder's avatar
pressure_welder
Explorer
Jan 24, 2016

Auxiliary in bed fuel tank question

Good afternoon everyone, hope all is well ! I have just finished installing a custom made tool box/auxiliary tank combo that I made up in my new 2015 ram cummins 3500 limited dually ( came from a 2015 duramax . With my particular setup I have an extra 60 gallons on board which will be awesome come towing season. The plumbing is setup like this.... 3/4" ball valve from the top of the suction tube, to a 10GPM 3/4" fuel pump, to a fuel/water separator, and then piped directly to a welded fitting on my stock filler neck. All of this is controlled via a "keyon" only switch.

Now my question is this... I was just curious whom of you have a similar setup to this? I know I am moving a fair amount of fuel with my pump, and I thought I would have adequate venting on the stock fuel tank on the truck however as you cummins guys know we have the capless filler neck with two flappers, and the vent location is just past the second flapper. It seems both flappers have to be depressed to create venting on the truck tank. I know there is a "high point" vent on the filler neck although I am not sure how much that does. Anyway I tested out the system and ran it for maybe 30 seconds which brought me from 3/4's of a tank to full. Just for curiosity i depressed both flappers in the filler neck with a screw driver and got a somewhat decent puff of air so I know I am building some pressure via the transfer pump. I am just curious to see what some of you may have done to remedy this issue? at this point I see myself taking off the filler neck assembly again, welding a bung on the vent tube and running another hose into the box with filter on it to provide venting. Am I missing something as far as the stock fuel tank venting adequately while both fuel flappers are closed? I would think there has to be a way for this thing to vent with both flappers closed? however I didn't hear anything hissing after I turned the transfer pump off.

take care!
Tow Vehicles
  • pressure_welder's avatar
    pressure_welder
    Explorer
    Jan 25, 2016
    eHoefler wrote:
    I have a 70 gph pump on mine, I ran a vent return line back to the aux tank. This helps in 2 ways, air is vented to the aux tank where the fuel is being removed, and for the times I forget to turn off the pump.


    thankyou! yes this was exactly my plan, a good fail safe for sure. I guess I thought there would be someway the tank would vent on its own without the flaps in the filler neck being depressed. All in all its not an overly difficult job to add this just should have done it when the filler neck was out the first time! thankyou for your input


    and yea unfortunately if you own a 1 ton up here it requires an annual safety inspection to insure its in good working order, and that the truck dosent break any laws such as being deleted (why I had to get rid of my duramax) and other various things. I guess its good and bad in a way.
  • eHoefler's avatar
    eHoefler
    Explorer II
    Jan 25, 2016
    I have a 70 gph pump on mine, I ran a vent return line back to the aux tank. This helps in 2 ways, air is vented to the aux tank where the fuel is being removed, and for the times I forget to turn off the pump.
  • lawnspecialties's avatar
    lawnspecialties
    Explorer
    Jan 25, 2016
    pressure_welder wrote:
    No worries fellas was just curious to see what guys have done out there. I considered gravity feed however it is illegal up here and I require yearly safeties. Plus I wanted the ability to fill quickly and push the fuel through a quality filter. I can fill my stocker in about 3 min. I believe my only option will be to tap into the existing vent line and run a hose back upto the aux tank to one of my spare ports ontop of the tank.... I was discussing with a friend and we figure the vaccume created by the pump in the aux tank will essentially in turn suck The air out that isn't being displaced in the trucks fuel tank via the stock vent tube.


    That's a bummer. Nobody down here checks anything like auxiliary tanks.

    In fact, I heard something real but hilarious the other day. I was listening to a local radio call-in show called "weekend trader". You can call in to sell stuff. They get ALL types.

    One guy was selling a late 90s F150. The fuel tank leaked and they could never find the leak and get it repaired. So he pulled the fuel line and it sits in a 5 gallon gas can in the bed of the truck. If you buy the truck, the gas can is included. I'm sure it wouldn't pass one of those "safeties" though. It must be gravity fed. :B
  • Bionic_Man's avatar
    Bionic_Man
    Explorer
    Jan 25, 2016
    lawnspecialties wrote:
    Bird Freak wrote:
    Wish I could help but both tanks I installed with RDS kit were gravity feed. No need for a pump.


    Ditto.


    X3. And I have never seen where gravity feed is illegal for diesel. But maybe there are places where it is.
  • pressure_welder's avatar
    pressure_welder
    Explorer
    Jan 25, 2016
    No worries fellas was just curious to see what guys have done out there. I considered gravity feed however it is illegal up here and I require yearly safeties. Plus I wanted the ability to fill quickly and push the fuel through a quality filter. I can fill my stocker in about 3 min. I believe my only option will be to tap into the existing vent line and run a hose back upto the aux tank to one of my spare ports ontop of the tank.... I was discussing with a friend and we figure the vaccume created by the pump in the aux tank will essentially in turn suck The air out that isn't being displaced in the trucks fuel tank via the stock vent tube.
  • lawnspecialties's avatar
    lawnspecialties
    Explorer
    Jan 25, 2016
    Bird Freak wrote:
    Wish I could help but both tanks I installed with RDS kit were gravity feed. No need for a pump.


    Ditto.
  • Bird_Freak's avatar
    Bird_Freak
    Explorer II
    Jan 24, 2016
    Wish I could help but both tanks I installed with RDS kit were gravity feed. No need for a pump.
  • YnotTurbo's avatar
    YnotTurbo
    Explorer
    Jan 24, 2016
    I installed a Transfer flow 50 gallon and the kit came with a T with a built in nipple to attach the hose from the aux tank for filling the main tank. I had to take off short vent hose, cut it, install the tee and clamp back on the main tank. Then I had to slide the hose from aux tank back on and clamp it as well. I know its not the same, but this is what the kit had. Pretty simple.
    Cut and past and look at page 10 of the instructions.
    http://www.transferflow.com/content/pdf/inst836.pdf

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