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Thread: Temp Gauge

  1. #1

    Default Temp Gauge

    I noticed that my temp gauge jumps from cold to max instantly after driving for a few minutes. I know the engine isn't overheating and the reading is incorrect. Could it be a bad sensor on the thermostat or a bad gauge? How do you go about diagnosing?
    I drove for over an hour today in 1st gear in 90 degree temps and no overheating. It would be nice to have an accurate temp though.
    Ray
    67 M725 & 83 FJ60

  2. #2
    Join Date
    Jun 2014
    Location
    Eastern Maine
    Posts
    377

    Default

    Sounds like a faulty sending unit, you can test it with a multi meter set to ohms. Should be about 3000 ohms cold, 1200 ohms @ 160 degrees, 917 ohms @ 180 degrees and 450 ohms @ 240 degrees. Disconnect the wire from the sending unit, attach one lead to the pin on the sending unit and the other to ground. I would check it cold and at normal operating temp.
    Last edited by m38inmaine; May 29th, 2018 at 12:57 AM.

  3. #3

    Default Temp Gauge Follow up

    I tried to follow your instructions but I am not sure my Multimeter is fancy enough to give me the correct reading. I set it at 20K and I got a reading of 4.16 at cold. I am guessing that is 4100? I touched the positive to the sending unit and the negative to the fuse box on the firewall. As I moved the lead on the sending unit, the reading kept changing. I am going to try it with the truck warmed up to see if it makes a difference. I know the gauge is working, it is just not accurate as it goes from 0 to max pretty quick.
    Ray
    67 M725 & 83 FJ60

  4. #4
    Join Date
    Jun 2014
    Location
    Eastern Maine
    Posts
    377

    Default

    You want to put the positive lead to the pin on the sending unit and the negative lead to the engine block.

  5. #5

    Default

    I am pretty sure that it is the Sending unit. The Ohms kept dropping as the car was warming up. I did also ground the wire to the sending unit and it sent the needle on the gauge to max. Do you know where I can find a sending unit?
    Ray
    67 M725 & 83 FJ60

  6. #6
    Join Date
    Jun 2014
    Location
    Eastern Maine
    Posts
    377

    Default

    The ohms are suppose to drop as it's heating up. Check the ground on the gauge.

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