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  • #16
    Tom, your original temperature sending unit is part # B7A 10884-A. It has a l/4"-18 NPT (national pipe thread). There are different sending units out there that are wrong. I just saw one on eBay. For instance, if yours says it was for a 1956, that year used 12-volt gauges. Yours are 6-volt. So, the part number I gave you STARTS with 'B7', which is 1957 and is carried on to subsequent years that used the l/4"-18 size hole.

    A proper resistance reading for a Ford temperature unit that is up to engine temp shoud be around 55-ohms, not 28-ohms. This is a RESISTANCE reading (with the wire off). reading from the unit's post to ground. With the wire ON, this should settle the needle just past the center mark.

    Remember, low resistance passes more current. A 'shorted' sending unit will show zero ohms. Your 200-scale is proper for this purpose. 28-ohms passes more current than 50-ohms, which sends the needle HIGHER.

    The numbers you cited (6 and 3.6) are voltages, before the gauge, then before the sending unit. These are normal 'voltage drops'.

    It's easy to measure a temp unit while it's cold and in the box. When you buy one, ask what the resistance is. Or, If you visit your local parts store, bring your meter. If it's out of range or the salesman simply 'doesn't know' then don't buy it. - Dave


    My latest project:
    CLICK HERE to see my custom hydraulic roller 390 FE build.

    "We've got to pause and ask ourselves: How much clean air do we need?"
    --Lee Iacocca

    From: Royal Oak, Michigan

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    • #17
      Dave, sorry if I'm being thick, but I'm not sure I understand. Is the 23-200 ohm range of my sending unit the problem or that it is reading 28 ohms for a warmed up engine or perhaps both? Out of the box, I should get 10 ohm reading, correct? I normally buy my bird parts from Carl Heller but went to local parts store for this one - looks like I should just get the right one from Carl, but I'd still like to learn as much as I can.
      Thanks
      Tom

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      • #18
        Tom,

        Dave is referring to an original Ford temp sender. Those units are no longer available new so unless you have a good used one you are stuck with an aftermarket unit. The Standard Products TS-4 that you have is one of the most popular replacements out there. If fits a number of different model cars, not just Squarebirds. Refer back to my post #7 to get the ohms readings for that particular sender. Looking at your picture the gauge is not pegged. The needle will go well past the dot when it's at max temperature. I have a feeling if you adjust/calibrate it you will be able to dial it in. My suggestion is to get the car up to around 180 degrees and adjust the gauge so it's about halfway between C and H. Then ground the wire and make sure it goes at least to the last dot if not further toward the H. That should get you close enough so you can tell if it overheats. These gauges were never very accurate to begin with so anything within 10-15 degrees is as close as you are going to get.

        John
        John Pizzi - Squarebirds Administrator

        Thunderbird Registry #36223
        jopizz@squarebirds.org 856-779-9695

        https://www.squarebirds.org/picture_gallery/TechnicalResourceLibrary/trl.htm

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        • #19
          Yes Tom, 23-200Ω is the WRONG sending unit, made for a different car altogether. Out of the box a cold temp sending unit should measure 100Ω. That is the same reading you should expect when your engine is cold.

          Let's put this in practical terms... Six volts trying to punch through 100Ω of resistance is going to have a hard time. Let's apply OHM's Law.. (voltage divided by resistance = current.) 6-v / 100-Ω = 0.06-amps. That's six one-hundredths of an amp is basically nothing. (We call it sixty milliamps.) If 100Ω is enough resistance to stop current, you sure have no need for 200Ω!

          Now, let's look at full scale... 6-v / 10Ω = .6-amps. Even though these numbers are small, just over 1/2-amp will produce enough heat to drive the needle to full scale.

          Your present sending unit produces 28Ω at 180F. So, 6-v / 28Ω = .21-amps. That's enough current to drive the needle over 3/4 of the way to full scale.

          When the engine temp reaches over 100F degrees (your body temp), the needle should just barely start to move to the 'C' on your gauge. When your engine is overheating, the sending unit resistance should drop to 10Ω. Half-scale is 100-10 or 90 divided in half or about 45Ω. Can you 'see it'? Lower resistance makes more current to drive the gauge needle higher. Resistance tests are always done with the sending unit's wire disconnected.

          Some good mechanics go their whole life without knowing why or how dash gauges work. They simply throw new parts at the problem instead of using proper tools to diagnose components. (Oxygen sensors - another part that can easily be checked with a meter on more modern cars.) - Dave
          My latest project:
          CLICK HERE to see my custom hydraulic roller 390 FE build.

          "We've got to pause and ask ourselves: How much clean air do we need?"
          --Lee Iacocca

          From: Royal Oak, Michigan

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          • #20
            Dave, I think I am getting it now. You're explanation of voltage and resistance helped. I'd like to also make sure I am testing for ohms correctly. Attached pic is a cold test on the original sending unit from my 59 bird (it's at least 40 years old so I assume it is the Ford type). It reads 38.2 ohms cold so I assume this SU is bad. I did the same test on my new SU (TS-4) and got 199 ohms.

            I emailed Carl to see if he has a SU that measures 100 ohms cold. If he does not and I cannot find it anywhere else, I assume my only choice is John's recommendation to use the new one and adjust the temp gauge?

            Thanks,
            Tom

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            • #21
              Tom,

              If Carl doesn't have one there's a number of NOS ones on Ebay. Here's some:
              https://www.ebay.com/itm/57-62-Ford-...sAAOSwHLRfE0-Y
              https://www.ebay.com/itm/1960-1963-F...YAAOSwEwZc6cuF
              https://www.ebay.com/itm/NOS-Ford-60...IAAOSwTZ9czHNH

              You want part numbers B7A-10884-A (not -B), C0DF-10884-A or part number C1AZ-10884-A. You want to make sure it's in a Fomoco, Autolite or Motorcraft box.

              John
              John Pizzi - Squarebirds Administrator

              Thunderbird Registry #36223
              jopizz@squarebirds.org 856-779-9695

              https://www.squarebirds.org/picture_gallery/TechnicalResourceLibrary/trl.htm

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              • #22
                Thanks John!

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                • #23
                  John, you may well be right. Modern sending units may start at 200Ω.
                  Tom, before buying a unit, ASK them to measure 'cold resistance'. They very well may be selling something you already have.
                  And yes, your old sending unit is bad. Its cold resistance is WAY too low.
                  My latest project:
                  CLICK HERE to see my custom hydraulic roller 390 FE build.

                  "We've got to pause and ask ourselves: How much clean air do we need?"
                  --Lee Iacocca

                  From: Royal Oak, Michigan

                  Comment


                  • #24
                    Looking at the map you are about an hours drive from Then and Now Auto Parts Weymouth Mass who specializes in antique parts. 781-335-8860. I've bought a few things from them. Good luck...

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                    • #25
                      Chris, I am Soooo glad you posted that because Then & Now Auto Parts IS a member of this Forum! She joined back in 2015, as I recall, after I talked with them regarding all the parts and services they offer and still do. As such, they give us free shipping on all Purchases! I just double checked this with Lisa and she confirmed it. In fact, in their Ad in the Advertisements Forum you will find that statement in bold. She said when ordering from them to quote that statement as a reminder to them that you qualify for free shipping. She has not been active on the Forum due to press of business, but she is still a member.

                      https://www.squarebirds.org/vbulleti...now-automotive

                      She said when ordering parts from them, send her a private message from the Forum. That way she will know you are a Forum member. See all the parts they have and the services they provide by clicking on the link above...

                      Ray Clark - Squarebirds Administrator
                      The Terminator..... VTCI #11178
                      Contact me via Private Message for my email address, or Call (Cell) 210-875-1411

                      https://www.squarebirds.org/picture_gallery/TechnicalResourceLibrary/trl.htm

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                      • #26
                        Thanks again all. Carl doesn't have any so I will check with Then and Now Parts. Will let you know how I make out.

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