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  • Temp Gauge Saga

    Hi folks,

    I've been working on getting all my gauges working and all are working except temp gauge. The temp gauge was sent out and professionally repaired and Dave Dare upgraded my CVR to solid state. When I got everything hooked up again I thought I was set when the temp gauge slowly worked it's way up but it did not stop until it reached max. I have a digital thermometer and was monitoring the temp as it went up. I could not get a temp higher than 180 no mater where I pointed it. I could easily release pressure using lever on rad cap and could then see that the thermostat was open thus everything looked OK. I assumed it was the sending unit. I read up on how to check resistance and while I'm no expert it seemed to me that the readings were not correct so I replaced it. As soon as I put in the new one I turned the key on and the temp gauged immediately pegged past max. I out the old SU back in and check some more things. When I remove wire from sending unit, gauge stays on cold which I believe is normal. When I ground the wire to engine temp gauge goes to max. Also normal from what I understand. Lastly, I checked the ohm setting on new SU, which is a standard parts TS4, and it is 200 ohms at room temp and about 23 at 180 degrees.

    Could it be that there is something wrong with both my old SU and the new one I bought? Any advice would be appreciated.

    Thanks,
    Tom

  • #2
    Tom, it could be a matter of adjusting the temp gauge reading. In the Technical Resource Library (TRL) push the Ctrl and the F (F=Find) buttons and type in Temperature Gauge. I will take you to the instruction for removing the gauge and adjusting the needle readings for the Fuel and the Temp gauge. It might just be a matter of making the adjustment. There are little pinwheels on the top for the top gauge and further down the gauge back for the lower gauge. It is a matter of adjusting the left or the right hand one to see if you can get the needle to move back towards the Normal or halfway position on the gauge...

    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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    • #3
      Thanks Yellow Rose for the quick reply and information. Would adjusting the gauge be necessary if the shop which fixed it told me they calibrated them? I don't want to mess with their work unless I have to. Also I should have noted that the gas gauge works fine.

      Comment


      • #4
        200 ohms at room temperature sounds way off. I would think it should be closer to 600 ohms. At 180 degrees it should be about 160 ohms. It sounds like your troubleshooting methods have been right on. It's certainly possible you got a bad sender right out of the box. If I can find a new sender in my stash I will check it to be sure. Even if it was out of adjustment it shouldn't go all the way to max.

        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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        • #5
          Tom, John has given you an idea as to why your temp gauge is not reading properly. Let's see what he has to say if he can find a spare sending unit and check it. He may be right about your old and replacement SU being bad... As for adjusting the gauges, let's see what he has to say about doing that also, considering whoever it was who fixed your gauges may or may not have "calibrated" it properly. You probably do not know what method they used to do that. You don't want to go that route if it happens to be a defective SU replacement, or a grounding problem...

          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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          • #6
            Sounds like a plan guys! Thank you.

            Comment


            • #7
              Tom,

              I didn't have a TS-4 to test but I found these specs on line. It sounds like your readings are correct. It could be the gauge out of adjustment as Ray mentioned but usually it's not that far out. I believe both the fuel and temperature gauges are the same. You could always swap the wires on the gauges and see if the temp gauge needle acts the same as the fuel gauge and vice versa. Just a thought.

              John

              221.3 73˚
              112.1 103˚
              88.8 114˚
              71.5 124˚
              55.4 135˚
              45.6 144˚
              37 150˚
              32 157˚
              27 167˚
              23.5 180˚
              22 185˚
              20 194˚
              19 200˚
              17 203˚
              14.5 212˚

              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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              • #8
                Yessss, I remember that Dave ~ simplyconnected recently said that those two gauges are the same, interchangeable.. That would be a good test, I would think, because if the temp gauge indicates correctly, and the fuel gauge goes whacky, that should tell you that there might be something wrong with the gauge... Or the wiring to that gauge... I would think that if the new solid state CVR unit from Dave had a problem with it, that both gauges would be acting weird. There should be an oscillating 0-6v getting to the gauges, certainly NOT 12v...

                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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                • #9
                  Thanks guys for the excellent advice. I switched the wires and the temp gauge read as the fuel gauge did before the swap and the fuel gauge went to full when the engine was hot. So, I figured it was the sending unit and I exchanged the the one I had just bought for another and ... almost the same problem. Needle did not go all the way to max but very close. Looks like you a were right and the gauge needs adjusting. I spoke with the guy who repaired them and he said I could send it back to him, but I may take your advice and try it myself. I think I remember seeing how to do in the the TRL. Will let you know how I make out.

                  Thanks again, you're always a big help.

                  Tom

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                  • #10
                    It doesn't sound like the gauge to me. If the temp gauge reads correct with the fuel wire hooked to it then it sounds like the gauge is calibrated correctly. You already know the fuel gauge is calibrated correctly so if it went all the way over to F when the engine got hot then it's not the gauge. Since you changed the sender the only thing left is the wire. I would use an ohmmeter to make sure the wire is good and doesn't have some sort of flaky ground on it.

                    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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                    • #11
                      Tom, I agree with John! Since the other gauge is doing the same or similar thing that the other gauge is after you swapped them, it sounds to me like the gauges are okay. I would not mess with adjusting the gauges yet. John might very well be right that it is not the Sending Units that are bad, but perhaps the wiring coming from it to the gauge. You do not know what might be happening to that wiring as it goes from the SU, through the firewall and then on to the gauge. You could have a frayed wire, or, as John said, a flaky ground.. So I would suggest that you either do as John suggested, or just run a brand new wire from the SU, to whatever it might have to go to first, before it goes to the gauge... John probably knows if it is a direct wire from SU to gauge, or makes a stop somewhere else along the way.

                      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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                      • #12
                        Sorry to be absent for a couple days but John was right there with sound advice (as usual). Thank You, John and Ray.
                        Ok, just a few things first... Ray, my CVRs output a solid six volts. It is rock steady regardless of ambient temperature or battery voltage. That's the main difference between a solid state and a mechanical CVR. Any 'variation' happens in the sending units, not the CVR. This power supply's output voltage is regulated. Current varies because the resistance in the sending units varies.

                        Yes, as John noted, both gauges are identical. They also operate with either polarity which is why there is no + or - designation meaning, you may swap the wires on the gauge and it will work equally as well. Ford gauges are NEVER grounded. If you measure a resistance to ground on either gauge post, someone wired it according to the GM scheme.

                        Resistance is a funny thing but I know both sending units (Fuel and Temp) to be variable between 10-100 ohms. Of course, 10 ohms lets more current through and it designates a full tank or hot engine producing 'full scale'. Is that total resistance? No, because the gauges also have resistance. That explains such high resistance that John posted. Meaning, the sending unit is in series with the gauge so total resistance for that circuit adds.

                        The internal 'arm' of the gauge (which is connected to the needle) is made of a bi-metal strip just like the old home thermostats used. Wrapped around the bi-metal is ni-chrome wire, much like a toaster uses to make heat only much finer.

                        So, HEAT, caused by current through the ni-chrome wire causes the bi-metal to bend (and thus, move the needle). When the metal cools (key off), the bi-metal bends back to its original shape. No motors, no brushes, no bearings, no polarity and nearly bulletproof.

                        Out of the box, both sending units may be measured with an ohm meter. The fuel sending unit has an arm which is pretty straight forward. The temp sending unit may be immersed in a pan of water and heated. Boiling water will not go above 212 degrees at sea level which is perfect for our test. Cold, it should measure ~100 ohms on the meter. At boiling, it should measure ~10 ohms. It's just that simple.

                        If I pulled the wire off of a sending unit and substituted a 50 ohm resistor in series to ground, the meter should register half scale.

                        Let's assume your temp wire is grounded, which would send the gauge to full scale. Pull the wire off at the engine and watch the gauge. Then, unplug the same wire before it goes through the firewall (on the engine side). The last portion (Red/White) goes from the firewall straight to the gauge with nothing else connected to that wire. Remember, Ford's wire color scheme. R/W can mean, a red wire with a white stripe OR a Red wire with a White END CAP. <--This informaton isn't in any of the Ford books.

                        Ray is right, this wire may be disconnected while you substute a temporary wire from the gauge to the sending unit. I welcome any and all questions so that everyone can get a better understanding, even if they were shy to ask. I come from Ford and this is my area of training and expertise. - 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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                        • #13
                          Dave, thank you for the commentary regarding Tom's gauge problem. It certainly adds to the conversation and gives us a much better understanding of how gauges work. You have certainly put your expertise to good use, after all those years at the Detroit Ford plants! Thanks for telling us that your solid state CVR unit has a steady 6v signal going through it, and not an oscillating one of 0-6v. I will keep that in mind when I talk about your solid state version in the future. Ya live and learn, and though I am an Old Dawg, I can still learn new tricks. Having read every post ever put on this Forum for the last 12+ years, I have learned so very much about Tbirds and automobiles that I will ever put to use... I know one thing for sure, and that is after looking at the engine bay of my 2017 Mustang, I will let the pro's take care of her! BTW, it has been nearly a year since I have owned her and I have put only about 6,000 miles on her so far and she is still a blast to drive! She certainly attracts a lot of good attention when I am out and about in her.

                          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

                          Comment


                          • #14
                            Guys, I did the following:
                            • I checked continuity of the Temp sending unit from the unit to the gauge. I also separated wire at firewall and checked each wire separately. All good.
                            • Just in case I ran a brand new wire from temp sending unit directly to gauge and heated engine up. Once it was warmed up (I'd say 180 degrees max) the temp gauged looked same as with original wire. Almost max (I will try and upload pic).
                            • I shut key off and went back to original wires again and restarted engine. Same reading on temp gauge.
                            • while the engine was hot and running I checked the volts at the temp gauge. From CVR 6 volts (shout out to Dave!) Other pole on temp gauge was reading 3.6-3.7 volts. Not sure what to make of other pole reading.
                            • At same time I checked resistance of sending unit itself in place on engine at ~180 degrees. It read approx. 28 ohms.
                            I am not an expert with the multimeter. For ohms, I set the dial to resistance and set meter on 200.

                            Dave, I am concerned the sending unit ohm range is ~23-200 and you mentioning the gauges call for 10-100. But if that were a problem, wouldn't the gauge be reading colder and not hotter?

                            Thanks again to all.

                            Tom

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                            • #15
                              Photo of gauges with engine warmed up.

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