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Coolant Sending Unit

Discussion in 'Early CJ5 and CJ6 Tech' started by tripilio, Oct 18, 2021.

  1. Oct 18, 2021
    tripilio

    tripilio Proud American! 2020 Sponsor

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    While fighting the gauge demons (grounding, replacing the voltage regulator with a 5vdc source, all kinds of fun!) I discovered something not quite right with my new coolant sending unit. According to a post from timgr (thanks for being so thorough) the resistance "cold" should be around 73 ohms. I am getting in the crazy zone of 500 ohms cold. I thought I had too much teflon on the threads but I checked between the threaded stud and the brass cap and the body as well with the similar results. Can anyone suggest a FLAPS part number that will work on a 62 F134? Maybe I bought the wrong one? Maybe I am measure resistance wrong? Any suggestion is welcomed! Thanks!
     
  2. Oct 19, 2021
    timgr

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    You understand that the sender must match the gauge, not the engine? Whatever sender that matches the gauge can go into the engine when you choose the fittings correctly.

    I would use no sealant on these senders. Teflon tape in particular could insulate the sender from ground. They are pipe thread, and should seal without any added goop. It'll be fine - the cooling system is not under extreme pressure.

    Post up which sender you used.
     
  3. Oct 19, 2021
    Lockman

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    X2 , with what Tim says on the teflon tape . We don't use it on sending units .'cuz they ground thru their bodies.
     
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  4. Oct 19, 2021
    tripilio

    tripilio Proud American! 2020 Sponsor

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  5. Oct 19, 2021
    timgr

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

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    Pretty darn expensive. $10 at RockAuto. The part for my 304 is less then $4, and would work. They should not call it a switch. Switch is on-off; this is a sender or sending unit.

    Test it in boiling water. The resistance should change when it warms up, and be in the range that your TSM specifies.
     
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  6. Oct 19, 2021
    tripilio

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    Thanks, timgr! Will test as soon as I can.
     
  7. Oct 19, 2021
    truckee4x4

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    Huh interesting - so is silicon gasket maker is a bad idea as well in terms of a bad ground?
     
  8. Oct 19, 2021
    timgr

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    I would not. Anything you put in there will worsen the connection. You need metal-to-metal contact for a good ground. Clean the threads and screw it in.
     
  9. Oct 19, 2021
    Glenn

    Glenn Kinda grumpy old man Staff Member

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    Don't they make thread lubricant for use in this type of application?
     
  10. Oct 19, 2021
    Lockman

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    Dielectric , or 'Tune - Up' grease . Non insulating & water proof .
     
  11. Oct 19, 2021
    timgr

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    By definition, a dielectric is a non-conductor. Any grease will probably be squeezed out of the joint enough for metal-to-metal contact.

    It's brass on cast iron - I don't think it's going to need any kind of thread lubricant. You could use copper anti-seize.
    Permatex® Copper Anti-Seize Lubricant

    Dunno, it's probably a moot point. Whatever you put in the joint will be squeezed out so there is good electrical contact regardless.
     
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  12. Oct 19, 2021
    Lockman

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    Hey Tim...... Did you ever hang out in a joint named " Cheers " ? :beer:
     
  13. Oct 19, 2021
    tripilio

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    I just tested my sender and in 175 f water reads 150 ohms. Definitively not the one!
     
  14. Oct 19, 2021
    timgr

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    You should check your FSM and not trust my numbers. Whatever I posted, it was for a '75.
     
  15. Oct 19, 2021
    tripilio

    tripilio Proud American! 2020 Sponsor

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    I have built a tester following (very loosely) your instructions and the gauge reacts correctly to those values.
    [​IMG]
     
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  16. Oct 20, 2021
    timgr

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    Outstanding! (y)
     
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  17. Oct 20, 2021
    truckee4x4

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    Neato! Can I borrow it next summer when you're done? :drool;
     
  18. Oct 20, 2021
    tripilio

    tripilio Proud American! 2020 Sponsor

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    Of course! I am about to be done. In about a week's time I will have done all electrical (hopefully!). PM me with your info so I can send it to you.
     
  19. Oct 21, 2021
    tripilio

    tripilio Proud American! 2020 Sponsor

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    I got another sender from another auto parts and even when it reads the same resistance cold, as soon as I immerse it in hot water it gets within range (73 ohms and below). Lets see what happens when the engine gets fully warmed . Oh, and also I don't plan to use teflon!:D
     
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  20. Oct 24, 2021
    tripilio

    tripilio Proud American! 2020 Sponsor

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    Ok, I am a little puzzled and frustrated. Tried the temp gauge outside...it works. Mounted it on the cluster and tried it...it works. Mounted the cluster and used the resistor box and it also works. Wire it to the temperature sender and...nothing! Right now the sender, after running the engine a little while engine reads around 32 ohms. If I set that resistance value on the test box the needle moves within a couple of seconds to the begining of the gauge. Could it be my 5vdc power supply that it is not strong enough? I used it outside and it moves the needle. Maybe since it is powering now both gauges at the same time... I don't know.

    IMG_20211024_090447_copy_1560x2080.jpg
     
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