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  1. #1
    FEP Power Member bridgener's Avatar
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    Default Temp Sending Unit Resistance

    What is the correct resistance measurement for a temp sending unit? I just replaced the original one on my 1982 Capri (which was reading over 1000 megaohms) with a Standard TS58T, which reads approximately 240 ohms at room temp. My gauge now gets pinned on hot after about 15 minutes of driving.

    I do have an infrared thermometer which I'll use to verify the engine temp next time I'm out for a cruise, just to see if the engine is actually getting too hot. I'm thinking that in my neck of the woods, 180-200 Fahrenheit should read within the normal range.

    ps - wow I haven't been here in a while!
    Brian

    1982 Capri 5.0L
    1965 Fastback project car - more rusty than not

  2. #2
    FEP Power Member
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    Default

    From JACook in a previous post.
    One of the quickest ways to become frustrated when working on cars, is replacing parts that
    you don't really know are bad. It's easy to test the coolant gauge and sender, all you need are
    a couple resistors and a $10 digital meter.

    Ground the sender wire through a 10Ω resistor. The gauge needle should settle within the width
    of the "H" mark. Then ground the sender wire through a 73Ω resistor. The gauge needle should
    settle within the width of the "C" mark

    The sender itself should read somewhere between those two values from the terminal post to
    ground, depending on the engine coolant temperature, unless they sold you the sender for an idiot
    light instead. Those are just on/off switches.

    Also, if you used Teflon tape on the coolant sender threads, it can insulate the sender from ground,
    preventing it from doing it's job. The resistance between the sender body and negative terminal on
    the battery should be < 1Ω. NB, There are exactly zero uses for Teflon tape on an automobile.
    To seal things like bolt and sender threads, I prefer Oatey white Teflon thread sealer paste. About
    $3 in the plumbing aisle at LowesDepot.
    Fox Body/3rd Gen MCA Gold Card Judge
    84 SVO 24K miles, 85 Mclaren Capri Vert. 84 GT Turbo Vert.
    88 Mclaren Mustang Vert 20K miles, 89 Mustang LX Sport Vert,
    03 Mach 1 7900 miles, 74 Mustang II, 69 Mustang, 67 Mustang, 07 GT500,
    14 Mustang CS/GT, 15 F150 FTX Tuscany, 16 F250 Crewcab, 67 Tbird 47K miles

  3. #3
    FEP Power Member bridgener's Avatar
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    Default

    Thanks for the reply, Kevin. I'll definitely test the gauge with those resistors just to eliminate it as a possibility.

    I'll also have to verify the engine temperature when the gauge is pinned just to confirm that there is some difference in the resistance of this sending unit, and what the factory spec should be. Assuming the sending unit isn't calibrated correctly, and the engine isn't running hot, I guess I can just add a resistor in series on the gauge wire to shift the needle to read correctly.
    Brian

    1982 Capri 5.0L
    1965 Fastback project car - more rusty than not

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