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Coolant Temp Sensor Identification

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  • Coolant Temp Sensor Identification

    On the diagram here:

    http://www.realoem.com/bmw/showparts...11&fg=35&hl=20

    There is no differentiation as to which coolant rail sensor does what. I assume one is monitored by the ECU, and the other goes to the gauge, correct?

    Which is which? I searched discussions with "sensor" in the title, but did not find this.

    Thanks in advance!
    Last edited by Ted B; 12-09-2007, 10:15 AM.
    2003 Mitsu EVO VIII - 2.0L / 600+whp
    1988 BMW M3 turbo - Work in progress. . .
    1986 SVO Mustang - Work in progress. . .

  • #2
    Originally posted by Ted B View Post
    On the diagram here:

    http://www.realoem.com/bmw/showparts...11&fg=35&hl=20

    There is no differentiation as to which coolant rail sensor does what. I assume one is monitored by the ECU, and the other goes to the gauge, correct?

    Which is which? I searched discussions with "sensor" in the title, but did not find this.

    Thanks in advance!
    Ted,
    The temp sensor that is monitored by the DME is the more expensive one. It is blue and shown as #5 in the diagram.

    The sensor for the coolant temperature gauge is #7 and it is brown.

    When looking at the diagram it is from the viewpoint as if you were standing at the front driver's side corner of the car looking through the engine at the coolant pipes. The left side of the diagram is towards the front of the car. So #5 is further toward the back of the car. When you look at your coolant rails you should see the blue sensor towards the back and the brown sensor towards the front.

    Good luck!
    Dominic

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    • #3
      That is exactly what I was looking for, many thanks. Given the fact that this car has 145k miles and I don't know much about its prior history (aside from Carfax), my better judgment tells me that I should probably replace both (and other sensors as well).
      2003 Mitsu EVO VIII - 2.0L / 600+whp
      1988 BMW M3 turbo - Work in progress. . .
      1986 SVO Mustang - Work in progress. . .

      Comment


      • #4
        Originally posted by Ted B View Post
        That is exactly what I was looking for, many thanks. Given the fact that this car has 145k miles and I don't know much about its prior history (aside from Carfax), my better judgment tells me that I should probably replace both (and other sensors as well).
        No problem Ted. If you have a multimeter you can test the blue temperature sensor by checking the resistance. It should read approximately 2000 ohms when "cold," at normal outside ambient temperature. It should read a few hundred ohms when "hot," after you have driven the car for awhile and just shut down the engine.
        Dominic

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        • #5
          Another thing to note is that the one with two prongs is for the DME and the one with one prong is for the gauge.
          "It is needless to say that self-propelling vehicles, like other machines, will never do as much for one who does not understand them as for one who does."

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          • #6
            I tend to replace these lil coolant sensors every couple of years just as good measure. Kind of like replacing O2 sensors, Tstats, and belts every couple years.

            Also, take an ohm meter and check your Throttle postion Switch. I checked mine last month, the Wide Open Throttle (WOT) portion was not working. If this switch fails your idle could be affected, and/or your full throttle maps might not be utilized.

            Mark M
            E30 M3 / E46 M3 / E83 X3

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