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Omix Fuel Sending Unit

Discussion in 'Early CJ5 and CJ6 Tech' started by wheelie, Oct 11, 2021.

  1. Oct 11, 2021
    wheelie

    wheelie beeg dummy 2021 Sponsor

    York, PA
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    OK......stupid question especially as anti-omix as I am. But.......here goes:

    Omix fuel sending unit for my '71 V6 (rear 15 gallon tank) may be the physical solution to the leak I had because the top of the sending unit appears to be correctly manufactured whereas the Crown part is not. The Crown part is stamped flat and does not have a slight flange/bevel stamped around the outside edge like the Omix part does and like the one I took out does. Without the flanged edge, there nothing on the sending unit side of things to help retain the O ring. This is what happened to me with the Crown part. The O ring somehow rolled out from under the sending unit. It was correctly installed on the tank before the tank went in.



    Also, the Crown unit has ports that stick up higher than the ports on the one I took out. It was a very tight tight fit up against the body tub. Maybe that had something to do with the O ring rolling out as well. Like if contact with the body, while wheeling, rubbed the lines and ports and moved the sending unit around a little. Certainly possible I believe. I am curious if the ports on the Omix are shorter.


    So, I guess my question is: Has anyone used the Omix sending unit in a rear tank and what were your findings? They list 2 different ones. One is specifically designated as for the V6 and costs 15.00 more than the other which is listed as fitting all cj5 with 15 gallon rear tank. Wondering what the difference is.

    Also wondering if it will last electrically. Dealt with a totally screwed up one for many years now. The Crown replacement got stuck on full the first time I filled the tank, though I have not ruled out a faulty gauge yet.

    I'll to add some pics to help clarify things later.


    Heres the link to the Crown unit. Maybe you can see the flat stamped area around the outside edge of the unit.

    Crown Automotive 5357373K 15 Gallon Fuel Sending Unit for 69-86 Jeep CJ Series

    And the Omix unit where you can see the stamped flange or bevel around the edge that help retain the O ring. The V6 specific part is similar in this respect but 15.00 more expensive.

    OMIX 17724.07 Fuel Sending Unit for 70-83 Jeep CJ Vehicle's with 15 Gallon Tank


    And finally the V6 specific part.

    OMIX 17724.04 Fuel Sending Unit for 67-71 Jeep CJ-5 & CJ-6 with 225c.i.
     
    Last edited: Oct 19, 2021
  2. Oct 11, 2021
    timgr

    timgr We stand on the shoulders of giants. 2021 Sponsor 2020 Sponsor

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    JMO - If I had choice between the Omix and Crown parts, it would be Crown every time. The clear lesser of two evils. From the pictures they look different, and I presume they are sourced from different factories.

    An alternative would be to buy your sending unit from MTS. They are probably selling the same part that Crown is selling, but they make their business selling gas tanks and supporting parts. MTS COMPANY, L.C. - Jeep CJ/YJ Gas Tanks Looking at that page, it appears that the "o-ring" they are selling has a rectangular cross -section. That's what I remember, but maybe I'm confusing it with my J10.

    I am sure that '67-71 Omix part is for the under-seat tank. Aftermarket is clueless about year ranges, and I presume, like everything else, Omix is worse than Crown. The later V6 under-seat tanks used a lock ring.

    I presume you have the original tank? There is a clear division in these tanks at '73-75 or '74-75. I am certain the '74 tank is the later design, and I don't have a '73 TSM to check. The design of the tank changes, moving most of the vapor recovery system plumbing to inside the tank, resulting in one liquid and one vapor line. The earlier tank has a nipple at each corner with five separate hoses to the expansion tank, or no vapor recovery. AFAIK the size and shape does not change '70-75.

    The original '74 part number for the sender is 994620. I can tell from this number that it originated around the 1970 time frame, with the introduction of the under-floor tank. That was superseded by 5357046, and again by 5357373 in 1977. The '77 part switches from a 2 3/4" sock to a 4 3/8" sock. Be sure to get a new sock that reaches the bottom of the tank.

    Dunno, I've had my tank out and back with no obvious issues. I know I replaced the hoses but I believe I reused the factory sender.
     
    Last edited: Oct 11, 2021
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  3. Oct 12, 2021
    wheelie

    wheelie beeg dummy 2021 Sponsor

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    Thanks Tim. I completely overlooked MTS. I’ll check it out.

    I just replaced my tank with the sending unit. The tank started seeping which is what started all of this. It was a replacement tank which I installed like 30 years ago when I put this keep together. The new replacement tank is identical in all respects as far as I can tell. The filler neck tubes at the right rear and 2 ports at the left rear whose original purpose I am unfamiliar with. Just like before, I’ve plugged one of them and use the other as a vent.

     
    Last edited: Oct 19, 2021
  4. Oct 14, 2021
    FinoCJ

    FinoCJ 1970 CJ5 Staff Member 2021 Sponsor 2020 Sponsor

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    Hey Dave...I don't know that I can answer your question exactly, but...I was digging around for other stuff in my junk collection today, and came across the old sending units I have from my tank projects....the longer 15 gal pick-up in this case was also a single outlet (no return), but I replaced it with one that had a return.
    [​IMG]

    Basically, what it appears to me, is the the 3rd one you list (OMIX 17724.04 Fuel Sending Unit for 67-71 Jeep CJ-5 & CJ-6 with 225c.i.) is for an underseat tank...its has a much shorter a different bend to the pick-up tube. The second one you list would be different and appropriate for the the rear 15 gal tank....As for the Crown part with the flat top - can't help you there.

    FWIW - I ordered both of my pick-ups from Walcks as they have an upgrade and replace the plastic float with a brass one. IIRC, when I spoke to them about it years ago, they just take the pick-up from their supplier, which I 'thought' was Crown, but could have been Omix, and just add their own brass float. Also, fwiw - which may not be much since I don't recall if they are Omix or Crown - both units have functioned electrically just fine for the 7 or so years I've had them.
     
  5. Oct 14, 2021
    FinoCJ

    FinoCJ 1970 CJ5 Staff Member 2021 Sponsor 2020 Sponsor

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    Sorry if I am just filling up your thread with useless info here...but took a picture of each of those old used parts....the one I pulled from the underseat tank looks like an Omix unit with the extra rim. Honestly, I don't think that rim was added to hold in the o-ring (although maybe it helps), but my guess is that the metal is so thin and flimsy that the rim was added in the stamping process to add a bit of rigidity. Its a pretty chintzy quality and guessing the 15 gal unit your looking at is no different. FWIW, this unit I pulled out looked barely used - still shiny and new looking as you can see - but I pulled because the wound resistor coil was broken and left the circuit open at all time - not a good sign for omix electrical durability.
    [​IMG]

    The crusty old one I pulled from the junkyard 15 gallon tank has the flat rim like the Crown unit - much better quality, although I don't know what brand etc...
    [​IMG]


    I believe those 2 small ports were for the charcoal canister vent system....Sounds like you have a good solution, but if it matters, I ended up looping (or maybe I should just say connecting) those two ports together with a short piece of fuel hose, and then I use a vented gas gap.
     
    Last edited: Oct 14, 2021
  6. Oct 14, 2021
    timgr

    timgr We stand on the shoulders of giants. 2021 Sponsor 2020 Sponsor

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    Hi James and Dave -

    That brass float is a Ford part that you can get through one of the classic Mustang specialist sellers. I have repaired them in the past with a bit of solder. A sunk float will be filled with gas, so I drilled a tiny hole in the corner and the gas drained out. After a few days of drying, the offending crack and the little hole I added were filled with a bead of solder.

    Sadly, this was in vain, since the float developed a new crack next to the one I repaired. A new float was ordered and installed.

    65-89 Mustang Fuel Sending Unit Brass Float

    Also, I presume that all the aftermarket senders now have a pickup tube and a return tube. You can always plug the return. The sender with a single pickup is probably OEM from 1970, with no return line. When present, the second nipple is used to return fuel to the tank and cause circulation in the fuel delivery lines.

    The two lines at the side of the under-floor tank are vapor lines used with the vapor recovery fluid check valve used from 1973 on. These are connected to the corners of the tank, so that one or the other is always above the liquid fuel level in the tank. If you have no vapor recovery system, you should be using a vented cap.
     
  7. Oct 14, 2021
    wheelie

    wheelie beeg dummy 2021 Sponsor

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    Thanks James. After Tim mentioned about the one unit being for the undersea tank, I did some ore searching and the more I looked at the pictures, the more convinced I became that you guys are correct about the differences in the pickup tubes. So, I ordered the Omix brand designated for use with the 15 gallon tank. We'll see how it goes. Not proud or happy because I don't trust their parts for the most part. But, with so few options, I had no better option.

    You may well correct about the intended purpose of the flange on the O-A part.......for added rigidity of a cheesy part. I do believe it helps retain the O ring as well so, perhaps an unintended benefit.

    FWIW, the MTS sending unit appears identical to the Crown branded unit.

    All of the locking rings this far ( I ordered one from NAPA for comparison) appear to be identical in dimension but the NAPA locking ring came with an O ring that has a rectangular profile, rather than round, which Tim alluded to with MTS unit, I think. So far, non of the locking rings are to my liking either as they seem thin and chintzy ( I like that word James) and should be of a greater overall diameter. In my mind, it should be impossible for it come out from under the tabs on the tank once it's started into position but, this is not the case. A tap to two in any direction with release it from it's position. We'll see what the O-A part looks like but I lay even money that it's the same as the others.

    Thanks gents. I'll update later. Parts should be here Saturday but not like to get installed until early next week. I got a Jeep show to attend. :bananatool:
     
  8. Oct 14, 2021
    FinoCJ

    FinoCJ 1970 CJ5 Staff Member 2021 Sponsor 2020 Sponsor

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    yes - the old rotted out o-ring from the JY is rectangular in cross-section, and I thought both of the ones I used with my Walck's/Crown replacements were also rectangular....The round o-ring would definitely be off-putting. Good luck....
     
  9. Oct 14, 2021
    wheelie

    wheelie beeg dummy 2021 Sponsor

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    See, now, I would think just the opposite. To me, the rectangular design would be more prone to rolling or twisting out of position whereas the round one would stay in place better. What am I missing from an engineering stand point on this?
     
  10. Oct 14, 2021
    FinoCJ

    FinoCJ 1970 CJ5 Staff Member 2021 Sponsor 2020 Sponsor

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    I don't know....its probably about the same....but when both the top and bottom surface is flat, seems like a flatter o-ring will sit there better as its getting squeezed down by the lock ring without twisting/rolling - which is one way that it can move or get squeezed out?
     
  11. Oct 15, 2021
    wheelie

    wheelie beeg dummy 2021 Sponsor

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    Okay. I'll buy that. My tank, however, has a "half round" groove stamped into it where the O ring resides, under the sending unit. Maybe not all tanks are like this but, for this reason, I will go with the round profile O ring.

    Sorry for no pics. I'm slipping.
     
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  12. Oct 17, 2021
    Downs

    Downs Kubota Orange Rattlecan

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    They were for fuel tank venting/emissions. I picked up a generic GM round charcoal cannister and the MTS liquid check valve. I routed those two to the liquid check valve then the top nipple on the check valve got routed to the engine compartment to the charcoal cannister and the vent for the cannister is routed to the airhorn on my stock air cleaner. To do it 100 percent right I should have a solenoid in there that closes off the vent line when the power is shut off but this has gotten rid of any raw fuel smell I did have and the vapors are burned instead of just released.
     
  13. Oct 19, 2021
    wheelie

    wheelie beeg dummy 2021 Sponsor

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    Pics added to earlier posts for some clarity.

    New sending unit from O-A :)shrug:) arrived Saturday. I'll get into it tomorrow evening. Gotta get this old heap running for the weekend.
     
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  14. Oct 23, 2021
    wheelie

    wheelie beeg dummy 2021 Sponsor

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    New sending unit from O-A arrived.




    All bent to h-e- double toothpicks right out of the box. Fortunately, I always keep my feathers numbered..........for just such an emergency. So, expecting garbage parts, I ordered two. The second one was not damaged and I installed it with success. Used the round O-ring. Painted the tank where the paint was destroyed from the previous leaking sending unit and installed the tank and skid plate. I put 13 gallons in it and so far so good, as far as no leaks.

    The pick- up and return ports are indeed lower on the O-A unit compared to the Crown unit so it fits better under the rear floor. There's a bit of breathing room whereas the Crown unit was right up against the floor. This O-A looks exactly like the part I took out originally back in July when I replaced the gas tank.

    Unfortunately, since the gauge ist kaputt, I have no idea if the float is set correctly. At some point, I'm sure I'll be doing this one more time at least. Gotta find a quality replacement gauge. But, I'm up and running. Nothing I drive has a working gas gauge so all is normal for my world. I'll have some time to look for an NOS gauge and maybe even NOS sender. Who knows what might pop up.
     
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  15. Oct 24, 2021
    Downs

    Downs Kubota Orange Rattlecan

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    I forgot to put in here when I made my post that my 76CJ5 is currently running an OMIX sending unit. When I first got it I hooked up my multimeter to it and make some swings on the float and the readings were all over the place. The wiper arm wasn't making good contact with the copper winding. A little futzing with the wiper arm and and adjustment of the float arm stops and I got it adjusted to within spec and it's been in there for a year next month and working fine. Knock on wood.
     
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  16. Oct 24, 2021
    timgr

    timgr We stand on the shoulders of giants. 2021 Sponsor 2020 Sponsor

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    Do you own a multimeter? Not sure what plugs and such the '71 wiring harness has ... you may be able to disconnect the sender wire between the tank and the dash. If not, disconnect at the cluster. Typically it's a pink wire. Measure the resistance to ground, and it should go like 10-23-73 ohms full-half-empty. It's not going to be impressively accurate, regardless.

    Not judging - this is something you should have done with the sender in hand. Use a tape and measure the depth of the tank. Then adjust the arm and stops so that you are at the top and bottom at the right resistance.
     
  17. Oct 24, 2021
    timgr

    timgr We stand on the shoulders of giants. 2021 Sponsor 2020 Sponsor

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    Does your temperature gauge work? On a CJ, the fuel gauge includes the "voltage regulator" which is a mechanical device that turns on and off to make a time average of 5 volts. This affects both the fuel and temperature gauge. It is possible to replace that regulator without replacing the gauge.

    Check my article here - Build A Gauge Tester This describes testing the gauge, not replacing the regulator.

    Also, the cluster must be grounded when power is applied. Do not test the gauges with the cluster not securely grounded to the dash. You will ruin the gauges.
     
  18. Oct 24, 2021
    wheelie

    wheelie beeg dummy 2021 Sponsor

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    I did measure the travel of the float and compared those measurements to the tank height. I believe it will be close when the gauge is fixed/replaced.

    I use an aftermarket volt gauge mounted in the dash, away from the factory cluster. The original volt gauge is longer hooked up. Hadn’t been for many many years.

    On a positive note, I had no leaks from a nearly full tank while bouncing around some sort of rough roads in Bald Eagle State Forest today. Not real rough but enough that a leak would have revealed itself.
     
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