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Water Temperature Reading Issues

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  • Water Temperature Reading Issues

    I have a 1996 Sea Ray with a Mercruiser MCM 5.7L. I have been troubleshooting the temperature by following this guide (https://itstillruns.com/test-water-t...t-7949115.html) because my temperature gauge is essentially stuck on ~190'F. It does not change when the engine is on before or after warm up. Key off it goes back down. Infrared readings indicate normal temperatures.

    My gauge appeared to be in working condition as it pegged high and low as expected. I replaced the sender unit as the ohm readings were not in range. The new sender unit still causing the gauge to get stuck ~180'F now.

    Any ideas on next steps?

  • #2
    Power and grounds are good. Key ON and sender wire grounded meter does peg hot. Sender disconnected meter goes to zero and new sender readings are the same

    I would say the meter is the issue.

    The sender uses 240 cold to 33 ohms hot
    If you could get a variable resistor and connect it to the sender lead and ground you could vary the resistance to see how the gauge reacts. Could also get a 100 to 120 ohm resistor and place it on sender lead and ground, it should be close to 1/2 gauge
    94 Formula 27PC Custom 509MPI MEFI3 , B3 XR
    95 Rinker 232 w/ 7.4L Carb 0F425011 B1 0F486471
    07 Seadoo GTX
    Merc Adults Only VP Adults Only
    G-Dad always said "First Liar doesn't stand a chance"

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    • #3
      I hooked up a 220Ω resistor to the gauge and it read 120'F.
      I hooked up a 100Ω resistor to the gauge and it read 165'F.

      It seems there may be excessive resistance somewhere in the wire. I took an ohm reading at the wire lead for the temp sender and it read 80Ω. Does that seem right or over? I unhooked the wire lead from the gauge and read the gauge resistance itself and it read 40Ω.

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      • #4
        80 ohms on a wire is a bit much

        But also 220Ω resistor and it reads 120* is off. At 220Ω it should read cold, gauge pegged low side
        94 Formula 27PC Custom 509MPI MEFI3 , B3 XR
        95 Rinker 232 w/ 7.4L Carb 0F425011 B1 0F486471
        07 Seadoo GTX
        Merc Adults Only VP Adults Only
        G-Dad always said "First Liar doesn't stand a chance"

        Comment


        • #5
          I also took a measurement of the wire lead at the gauge with the sender hooked up and got a reading of 410Ω at 86'F. Does anyone have a chart that shows the input Ω curve for a Sea Ray water temp gauge?

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          • #6
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            94 Formula 27PC Custom 509MPI MEFI3 , B3 XR
            95 Rinker 232 w/ 7.4L Carb 0F425011 B1 0F486471
            07 Seadoo GTX
            Merc Adults Only VP Adults Only
            G-Dad always said "First Liar doesn't stand a chance"

            Comment

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