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Converting Fuel Tank From 62 Cj5 To 78-83 Design Questions

Discussion in 'Early CJ5 and CJ6 Tech' started by _fletch_, May 9, 2020.

  1. May 9, 2020
    _fletch_

    _fletch_ New Member

    Kentucky
    Joined:
    Jul 8, 2019
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    14
    I know there's probably a million threads about this, but I'm not getting my questions answered through my research so far.
    As the title says, we're converting my son's 1962 CJ5 fuel system. Someone had already abandoned the mechanical fuel pump before we got here, but we removed the small tank from beneath the driver's seat, and cut out the x-bracing in the rear and installed a steel 15 gallon tank from Crown. (See the attached pic)
    So I have several questions.

    1. The electric fuel pump someone had already converted the old tank to pulled off the bottom. Is there anyway to know for sure it will be capable of pulling off the top of this new tank? (See other attached pic)
    2. The sending unit was never hooked up on the old one. The previous owner was using a yard stick to check his level. There was only the old instrument cluster with a fuel light, but of course was not working. This new sending unit has an insulated post and a tab soldered on the cap. I'm assuming we run a wire from the grounded tab to frame ground? And then run another wire from the sending unit post to a fuel gauge? Is there a certain fuel gauge you all would recommend?
    3. How important is it to install a fuel liquid check valve and run the two fuel tank vapor vent lines to it? I was told I could just hose them together as shown in the picture but that may be a bad idea.
    4. If I do use the check valve and vapor vent lines, I guess I then run the liquid check valve to cannister hose back to the fuel tank cap? (The other hose I have capped off)
    I have a gut feeling that if we don't use the check valve/vapor vent lines we may lose purge on the fuel system, or vapor lock the fuel line, but obviously we are novices at this so I don't know. I'm sure these are extremely newb questions, but we're getting ready to set the tub back on this thing and I'd like to not have to pull it off again, or drop the gas tank from underneath.

    I appreciate your time.
    IMG_1282.JPG IMG_1283.JPG
     
  2. May 9, 2020
    Twin2

    Twin2 not him 2020 Sponsor 2019 Sponsor

    Virginia Beach, VA
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    I see your using a later model tank . small inlet and vent . on drivers side ?
    anyway filler neck should look like this . but this would be a closed system with a carbon canister . non vented

    [​IMG]
    as to check valves ? do you really need them
    as to fuel pump . hook it up and see if it will suck the gas out of tank
     
  3. May 9, 2020
    colojeepguy

    colojeepguy Colorado Springs 2019 Sponsor

    At the foot of...
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    You want to mount that pump as close as possible to the tank, and as low as possible.
     
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  4. May 9, 2020
    _fletch_

    _fletch_ New Member

    Kentucky
    Joined:
    Jul 8, 2019
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    The filler inlet and vent are on the right hand side of the picture (driver side for reference), and I'm pretty clear on them. I have the same filler neck as shown in your picture. Appreciate the reply, but unfortunately, that wasn't what I was asking about. I was asking about the two vapor lines coming off the gas tank that are on the left hand side of the picture, that I have hose connected together. Technically, they are supposed to go to a check valve and NO, I don't know if I really need them, which is why I was asking.

    As far as just hooking it up and seeing if it will pull gas, sure I could do that, but I don't like taking two steps forward and three steps back. I'm trying to get it right the first time. I don't want to re-install all the body and then find out I could have avoided a lot of aggravation by asking questions now.

    Thanks.
     
  5. May 9, 2020
    _fletch_

    _fletch_ New Member

    Kentucky
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    Jul 8, 2019
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    That's a good point. We've increased the distance the fuel will have to travel quite substantially. Any thoughts on any of my other questions?
     
  6. May 9, 2020
    timgr

    timgr Eppur si muove. 2020 Sponsor 2019 Sponsor

    Medford Mass USA
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    Yes, pump close to the tank and low.

    Cap the pair of 5/16" ID vapor recovery lines coming off the side of the tank and use a vented gas cap. A '62 has no provision for vapor recovery and those two lines are superfluous. You would need significant study and effort and scrounging to install a vapor recovery system.

    You can use the original gauge in the existing cluster. What year and model is this tank sender for, specifically? The ohms range of this sender should match the factory gauge.

    upload_2020-5-9_14-19-51.png

    This is for 1975; should be the same as your factory gauge and that sender. Look in your TSM. I believe all of the CJ senders have these specs, but it we should check what sender you are using. You could also use any aftermarket gauge that expects this resistance range from the sender - look on Jegs or Summit and pick what you like.

    Yes, insulated stud goes forward to the gas gauge, and connection on the top disk of the sender goes to ground. It's a variable resistor.

    The capped hose is a fuel return line, not a vent. Later Jeeps circulated fuel from the tank to the fuel pump and back to keep it cool and prevent vapor lock. Not a bad feature, but again '62 was way before that and the Jeep will work fine without it.
     
    Last edited: May 9, 2020
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  7. May 9, 2020
    _fletch_

    _fletch_ New Member

    Kentucky
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    Jul 8, 2019
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    IMG_1284.JPG
    Thanks so much for the thorough response!!!

    Here's a pic of the original cluster. I'm assuming it was original for the '62? It looks like it only had a light for fuel... no gauge, and as I mentioned before was not even hooked up. So I think I'm going to need a new gauge.

    The new fuel tank sending unit is supposed to be for models 78-83. It has these numbers on it. J5357373 and 218120216

    So I've already hosed those vapor recovery lines together... ought to be just as good as capping them right? And I have the return line capped. So I'll mount the pump close to the tank and as low as possible.

    Thanks again.
     
  8. May 9, 2020
    timgr

    timgr Eppur si muove. 2020 Sponsor 2019 Sponsor

    Medford Mass USA
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    Gauge is just missing, I'd say. Fuel Gauge Dash Unit Replacement 1957-75 CJ5, CJ6 1957-64 CJ3B, Pick Up Truck, Station Wagon, Sedan Delivery, FC
    Never seen one with a fuel light.

    This is for '79: upload_2020-5-9_15-6-14.png

    535 7373 is correct for '77-80 (1980 is as far as my book goes). It should have a 4 3/8" long sock. I presume you got a tank for a '78 or newer.

    You'll need a vented cap, otherwise you'll pull a vacuum above the fuel as the tank empties. You can use a sealed cap if you run a vent high up into the fender from the vapor recovery lines. A fuel filter works well as a vent cap.
     
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  9. May 9, 2020
    melvinm

    melvinm Member

    Arvada Co. 80003
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    I used the same setup in My 1974 CJ5 , I grounded the tank to the frame and hooked the
    sending unit to the gauge in the instrument panel every thing worked fine.
    You do need to vent the tank . I vented it using A roll over valve on the fire
    wall but not happy with that , I need to find something different.
     
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  10. May 10, 2020
    _fletch_

    _fletch_ New Member

    Kentucky
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    I have a vented cap and the filler neck that Twin2 posted earlier, so that should work, right? Also, there's no need to use the sending unit sock if I'm running an inline fuel filter between the pump and carb is there? This tank will have limited access in the future, and I don't want a stopped up screen in a tank to deal with. Thanks for all the help.
     
  11. May 10, 2020
    timgr

    timgr Eppur si muove. 2020 Sponsor 2019 Sponsor

    Medford Mass USA
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    You need a vent of some kind. In its original application, the tank was vented through the vapor recovery system. If you have a vented cap, that will work fine. It should say "vented" on the cap.

    Pretty sure you need the sock - it should have come with the sender. I believe the pickup reach into the tank won't be complete without it, and you'll sacrifice some tank volume. It won't get stopped up if you put clean fuel in the tank. It's a new tank, right?
     
    Last edited: May 10, 2020
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  12. May 11, 2020
    BadGoat

    BadGoat How High Can You Climb?

    Northern Virginia
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    Take the time now and install an access door in the rear bed. At some point you will need to mess with the sending unit or hoses, and they are a pain to get to otherwise. I had to cut my floor after the body was back on.

    6-1/8" x 6-1/8" Floor Access Door


    Mike
     
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  13. May 13, 2020
    _fletch_

    _fletch_ New Member

    Kentucky
    Joined:
    Jul 8, 2019
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    After seeing your post, we went back and installed the sock, as I believe you're dead on about sacrificing tank volume without it. Yes, it is a new tank, and we plan to only use ethanol free fuel in it. There's still a gas station or two around here where you can get the good ole stuff.

    Thanks again for all the advice.
     
  14. May 13, 2020
    _fletch_

    _fletch_ New Member

    Kentucky
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    Thanks, we've been talking about that.
     
  15. May 31, 2020
    66cj5

    66cj5 Jeep with no name

    NorthWest Indiana
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    Sep 10, 2003
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    2,089
    If I had to redo this mod, I'd use all 1978 model year parts (tank, neck, hoses, skidplate, and mounting bracket) instead of the 1970 tank with a modified neck to fit 1978 parts.

    A good recommendation is to glue a small but powerful magnet to the corner away from the intake to keep any future rust out of the gas system.
     

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