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Adding A Gas Tank

Discussion in 'Intermediate CJ-5 and CJ-6 Tech' started by Andy Salagaj, Jul 31, 2018.

  1. Jul 31, 2018
    Andy Salagaj

    Andy Salagaj Joshua70x7

    Colorado
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    Aug 3, 2016
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    Can I add an under seat tank to my 73 CJ5? Is there a kit available or has anyone done this? I'd love to have an extra few gallons on longer trips.
     
  2. Jul 31, 2018
    47v6

    47v6 junk wrecker! Sponsor

    Washington DC.
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    Oct 25, 2006
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    73 has rear mounted, right? Can you buy the poly 21 gallon one?
     
  3. Jul 31, 2018
    timgr

    timgr Jeepin' Nerd Sponsor

    Medford Mass USA
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    There's no kit. I added an under seat tank to my '73 CJ-5 in 1973. You just buy the parts and install them. It's been a popular mod since 1970, when the main tank moved to the rear. You can also remove the tool box and put an under-seat tank on both sides. Mirror image tanks are available.

    It's not all sunshine and roses though. You have to cut the body that goes around the filler neck. You need to add the body part for the filler. These tanks tend to leak out the filler, since the filler is so short and low. The leakiness plus the necessary vented cap means that they always stink of gasoline. The stinky filler is right under your left elbow. There is no easy way to make the tank emissions legal.

    But you can do it. It's not difficult.
     
  4. Jul 31, 2018
    dane71

    dane71 New Member

    USA
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    May 11, 2017
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    Now might be a good time to bring this up. But for a while I've had an idea... I could add this rollover valve to the neck of the under seat tank, plug or switch the cap to non vented, and tee the rollover valve into the line going to the charcoal canister. Is that a feasible solution?
     
    Last edited: Jul 31, 2018
  5. Jul 31, 2018
    timgr

    timgr Jeepin' Nerd Sponsor

    Medford Mass USA
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    Possible. I tried something similar, tying a nipple in the filler neck into the vapor recovery system. If you take the vent back to before the fluid check valve in the vapor recovery, it might work ok. There is a labirynth in the vented cap that nominally stops slosh from coming out the cap; I plugged that with some liquid steel and tried to rely on the vent in the filler neck. The cap never sealed well enough to keep the Jeep from stinking though. Slosh would always leak out around the cap, and it does not take much for it to smell like gas.

    I did all this when I was 19, and maybe I could could make it more successful today. The dealership where I worked kept the black steel Stant replacement cap for these tanks in stock because the price was about half of what they cost through the Jeep parts network. I pulled all the pieces I used from parts department stock. Maybe there is a better cap, or a better gasket for around the cap.
     
    Last edited: Jul 31, 2018
  6. Jul 31, 2018
    timgr

    timgr Jeepin' Nerd Sponsor

    Medford Mass USA
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    Note to the OP - as Chris mentioned, there is an oversized replacement tank available from MTS. Hangs down a little more than the factory tank, but gives you an additional 7 gallons. The under-seat tank is only 11 gallons. 0050XL MTS COMPANY, L.C. - Jeep CJ/YJ Gas Tanks
     
  7. Jul 31, 2018
    heavychevy

    heavychevy Sponsor Sponsor

    Danielsville georgia
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    Glad this was brought up. Like having a reserve on my 74. Already have a underseat tank out of a 70, cj.
     
  8. Aug 1, 2018
    Andy Salagaj

    Andy Salagaj Joshua70x7

    Colorado
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    Aug 3, 2016
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    Tommy, have you had any leaky problems or fumes. If i go forward with this I don't want either problem. My stock tank is basically brand new so I am looking at other options for more fuel. I could always add fuel cans mounted on the rear - that may be the easiest option. Either way it gonna cost a few bucks but I'm willing to do that for the extra fuel.
     
  9. Aug 2, 2018
    heavychevy

    heavychevy Sponsor Sponsor

    Danielsville georgia
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    Yes, it does have some odor. It is not too bad though. Venting thru the emissions canister helps. Good feeling keeping an extra tank full, for hunting trips
     
  10. Aug 2, 2018
    heavychevy

    heavychevy Sponsor Sponsor

    Danielsville georgia
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    Might add too if i were doing this again i would look at the bigger poly tank. The Poly tank will need a skid plate under it though. If your jeep does not have a skid plate, you will need one to cover the vulnerable plastic tank.
     
  11. Aug 2, 2018
    timgr

    timgr Jeepin' Nerd Sponsor

    Medford Mass USA
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    All the plastic tanks rely on steel bands to hold them down. From '76 on, the skid plate was standard because it supported the tank and there was a strap across the top to keep the tank from shifting on the skid. The 1970-1975 tanks bolt into the frame, and the skid plate is an optional accessory, so these tanks will stay up in the frame without the skid plate.

    If your '70-75 Jeep does not have a skid plate, the '76-up plate can be made to work and is available aftermarket as I recall. Pretty sure you can't have a plastic gas tank unless it's sitting on something - it does not have the long-term structural strength to support itself from above. MTS only sells plastic tanks, so any '70-75 Jeep with one of their tanks must have a skid plate, regardless of whether it's original capacity or oversized.
     
    Last edited: Aug 2, 2018

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