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Underseat gas tank woes

Discussion in 'Early CJ5 and CJ6 Tech' started by JK67CJ5TX, Sep 4, 2004.

  1. Sep 4, 2004
    JK67CJ5TX

    JK67CJ5TX Member

    El Paso, Texas
    Joined:
    Oct 24, 2003
    Messages:
    81
    Until Wednesday, I ran on an underseat tank. I now have two on the used parts stack. The first tank was original, and was fouled beyond belief from sitting for fifteen years in a barn. When looking for a replacement, I could only find replacements for the four cylinder engines. I figured it couldn't make a big difference so I bouhgt one for the four banger and adapted fittings and went off to the races! All was well until the spring temperatures and altitude conspired to create a chronic vapor lock. Do not try this with a :v6: ! I took a lesson from Boyink and installed a 15 gallon tank from a later model CJ. On opening day of Dove season, Wednesday, with about thirty minutes to go to departure, I installed new fuel and vent lines on the new tank, pulled the old tank and lines; connected the sending unit wire to the existing original equipment guage and the problem is now solved. Mr. Boyink's web page has a good description on how to accomplish the tank change and I recommend it to all. I now have a very smooth running :v6: and the piece of mind that I no longer sit on a bomb.

    JK
     
  2. Sep 4, 2004
    James P. Enderwies

    James P. Enderwies Sponsor

    Lake Havasu City, AZ
    Joined:
    Feb 2, 2003
    Messages:
    747
    JK: Were you running the 3 port fuel pump with the return line to the tank? Had no problem with mine here in 121* temps! :)

    Don't mind the tank under the seat. At least if I get hit in the rear, it won't bust. Course, I'm "Old School". R)
     
  3. Sep 4, 2004
    Boyink

    Boyink Super Moderator Staff Member

    Tulsa, OK
    Joined:
    Sep 20, 2002
    Messages:
    6,193
    Thanks for the comments, JK.

    I'm considering running dual tanks in SSDutch. The PO installed a new underseat tank/sender, and I don't have the same need for the storage space that I had in Dutch.

    Kinda thinking 25 gallon capacity might be nice.
     
  4. Sep 4, 2004
    JK67CJ5TX

    JK67CJ5TX Member

    El Paso, Texas
    Joined:
    Oct 24, 2003
    Messages:
    81
    Jim ,

    I have the three port fuel pump. The problem is with the fuel line fitting at the tank. Since the fuel tank was intended for a four cylinder engine, it had provisions for a 1/4" line, not the 5/16" the :v6: uses. So when a large fuel demand was placed on it, the fuel pressure dropped to a low pressure, possibly negative, and bubbles formed. This interupted the fuel flow, even with the return line, to the point that the engine would starve. I found that once the bubbles formed, the engine would continue to starve as long as you ran it. This also weakened the rubber hose sections to the point that they would collapse. With the new tank and new stainless steel 5/16" lines from the tank to the fuel pump, all is now well. In any case with a collision, the new fuel tank is further from me. As Mike metnioned, I thought about keeping both tanks for a minute or two, but opted out. I don't need the additional headache, and even my cross country forays into the desert won't exhaust fifteen gallons of fuel. I also carry two five gallon jerry cans, just in case. This gives me about a 250 mile range offroad, and an onroad range of about four hundred miles. Even out here in the wilds that is a long way. that translates to driving offroad to Tucson, and onroad to Abilene. If I'm going that far I'll use the Tahoe.

    JK
     
  5. Sep 4, 2004
    James P. Enderwies

    James P. Enderwies Sponsor

    Lake Havasu City, AZ
    Joined:
    Feb 2, 2003
    Messages:
    747
    JK: Interesting! I bought a NOS tank that had been used for 1 year from a member. It was the guy that had his father in law build a Jeep and it got totaled 3 months after it was finished. Tank only had gas in it 1 year. It's excellent shape with a new sending unit that I checked out with the OHM meter and it works fine. BUT, it doesn't have the return line. NBD, I'll just take it down to the rad shop and have them braze one in.

    I just went and checked it, and guess what? It's a 1/4" feed out of the tank!!! :shock: So, when it's at the rad shop, I'll have them braze in a 5/16" outlet fitting also. :)

    Thanks for the input.
     
  6. Sep 4, 2004
    Warloch

    Warloch Did you say Flattie??? Staff Member

    Falcon, CO
    Joined:
    Mar 4, 2003
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    5,466
    Interesting - Been running with a '4 banger' tank on my V6 since 76 without any problems...

    :stout:
     
  7. Sep 5, 2004
    James P. Enderwies

    James P. Enderwies Sponsor

    Lake Havasu City, AZ
    Joined:
    Feb 2, 2003
    Messages:
    747
    Fuel Tank

    Warlock: I kind of agree. Many years ago, I owned a '64 Chevelle Malibu SS. It had a 5/16 fuel line on the orig. 2G 2 bbl (changed out to a 4 bbl). In '67, I think, a good friend of mine went to the Ford dealer to look at the new Shelby 350 GT Mustang. Guess what, it had only a 1/4" fuel line on it! :? :shock:
     
  8. Sep 5, 2004
    mb82

    mb82 I feel great!

    Charlottesville Va
    Joined:
    Mar 17, 2003
    Messages:
    2,706
    yep guys i never thought the fuel line could be too small for these small motored jeeps. hmmm i will have to see what if any problems i have.
     
  9. Sep 5, 2004
    66cj5

    66cj5 Jeep with no name

    NorthWest Indiana
    Joined:
    Sep 10, 2003
    Messages:
    2,084
    get a 1/4" to 5/16" adaptor.
     
  10. Sep 7, 2004
    JK67CJ5TX

    JK67CJ5TX Member

    El Paso, Texas
    Joined:
    Oct 24, 2003
    Messages:
    81
    FWIW, I had an adaptor made for the tank I just replaced. Now i have 5/16" new line all the way from the tank to the fuel pump. I've test driven the Jeep over the same routes where the problems previously occured. Overall performance is improved and there are no indications of any trouble.

    JK
     
  11. Sep 7, 2004
    James P. Enderwies

    James P. Enderwies Sponsor

    Lake Havasu City, AZ
    Joined:
    Feb 2, 2003
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    747
    JK: Did you actually replace the 1/4" outlet in your tank with a 5/16" one, or did you just use a 1/4" to 5/16" adaptor?
     
  12. Sep 7, 2004
    jpflat2a

    jpflat2a what's that noise?

    Hermosa, SD
    Joined:
    Jul 30, 2003
    Messages:
    8,513
    if you just use the adapter you still only have a 1/4" outlet :D
     
  13. Sep 8, 2004
    maxx

    maxx Banned

    Menlo Park, Ca
    Joined:
    Apr 22, 2003
    Messages:
    171
    heres my two cents. raw gas smell under your seat? get it fixed. Its leaking. Moving your gas tank a few feet to the rear? It aint gonna save you. Seams burst under compression, and its still raw gas. You might save a micro second or two.
    In a collision from the front, the rear end is still travelling at several mph faster than the rear end.
    If you pursue this scenario with illusion of safety, youre just switching seats on the Titanic.
    These old farm vehicles were never made to be a freeway cruiser, and they never will be.
    Just my two cents. Sorry if you take offense.
     
  14. Sep 8, 2004
    manden68

    manden68 Member

    O Fries Country
    Joined:
    Jul 16, 2003
    Messages:
    214
    I concur in regards to the whole accldent scenario. However, concerning the "farm" postulate- my jeeps been to the mall, to get pizza, my old girlfriend cut my hair it once, been to the drive-in, been underwater, shot a 10gauge out of it, had a couple surfboards stolen out of it. Never any farm activities. You know,hard-core 4X4 stuff.
     
  15. Sep 8, 2004
    blevisay

    blevisay Oh Noooooooooooooooo! Staff Member

    Portland Tn.
    Joined:
    Sep 20, 2002
    Messages:
    4,348
    R) R) R) R) R) R) R)

    You cut you Hair????? :rofl:
     
  16. Sep 8, 2004
    JK67CJ5TX

    JK67CJ5TX Member

    El Paso, Texas
    Joined:
    Oct 24, 2003
    Messages:
    81
    Whoa!!! Now all you buckaroo's just take a pill! I never meant to start an argument over underseat tanks. I only meant to provide a little information to those of you who desire to move the fuel to a more distant location. My comments about the underseat landmines/bombs were meant for humor! As far as safety goes, you are no safer than the nut behind the wheel!

    OK, now that you are calm, I'll answer Jim's question. I had the fuel hose adapted to fit the 1/4" fitting in the tank. So, yes, I was pulling the fuel through an orifice that is about 3/16" ID. That is what caused the low pressure in the line, and hence, the bubbles. I have read here before that several people have just taken the four-banger tanks to the shop and had the proper fittings welded on to handle the :v6: . I drilled and tapped the fuel filler neck to accept the return line for the original tank and robbed the return fitting off of the original tank. Had I drilled out the 1/4" fitting and made arrangements for connecting the 5/16" fuel line in the first place, we wouldn't be having this chat. However, I must confess, I have never felt comfortable sitting on a gas tank.

    All of that said, I appologize for creating a riot on this forum.

    JK
     
  17. Sep 8, 2004
    ljspop

    ljspop Lurking Bronco Dude

    San Diego, CA
    Joined:
    Jan 29, 2003
    Messages:
    394
    That's what I did for my tanks. :D
     
  18. Sep 8, 2004
    vanguard

    vanguard

    I thought you had poly tanks. :D
     
  19. Sep 8, 2004
    James P. Enderwies

    James P. Enderwies Sponsor

    Lake Havasu City, AZ
    Joined:
    Feb 2, 2003
    Messages:
    747
    Jim, that was the point of my question. :D Sounds like thats what JK did.

    JK: Wanna have some fun? Ask about "Flat Towing" or "Knuckle Pudding" :twisted: R) R) R) (Sorry guys, couldn't resist! :twisted: ) R)
     
  20. Sep 8, 2004
    speedbuggy

    speedbuggy Looking for a Jeep now

    Living the Good...
    Joined:
    Jul 1, 2004
    Messages:
    1,270
    To add to the madness, I am going to replace the underseat tank with a fuel cell from Summit. It will be mounted in the rear cargo area, just behind the seats. I am doing this for 2 reasons:

    1) It will be nice to be able to see the fuel inside when you open the lid. I'm sick of not having a gas gauge.

    2) I need to move the drivers side seat a couple of inches lower. This will help.

    fwiw, there is a sbc under my hood... Still using the original tank. Never had a problem with fuel supply.
     
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