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Thread: Strange Coolant Temp Reading

  1. #1
    Join Date
    Feb 2015
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    Kuna, Idaho
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    Strange Coolant Temp Reading

    1990 German spec 750i "Shortie"

    On Wednesday afternoon, I drove the car and the temp gauge was reading it's normal 11:59, no problem. The next day (thursday), I drove the car and now the temp gauge won't go above the area between the blue area and the first mark on the left of the gauge.

    Is this a temp sender issue, or is my gauge suddenly screwed up, or worse some bizarre "module" issue.

    Head scratch time...

    Thanks in advance
    Mike Drives:
    BMW's
    E24 - 635CSiA - (1) 1985 (US)
    E24 - 635CSi - (1) 1985 (EC)
    E31 - 850iA - (1) 1991 (Black)
    E31 - 850iA - (1) 1991 (Calypso Red)

    E32 - 740iA - (1) 1994
    E32 - 750iA - (1) 1990 (Not an "L") (EC German National)
    E32 - 735iL - (2) 1990
    E32 - 750iL - (1) 1990

    E38 - 740iLA - (2) (1) 1997 & (1) 1998
    E38 - 750iLA - (1) 1998
    E38 - 740iA - (1) 2000 "Short Sport"
    E39 - 528iA - (2) - 2000 & (1) 1997
    Also:
    2015 Ram 3500 Dually, Cumins 6.7, Std.Cab. Long box 4x4 (To haul all this junk when necessary)
    2014 Dodge Dart Rallye (Daily Driver)
    2007 Mercedes Benz CL600 (Brabus SV12S)
    Mercedes Benz SL's - (1) (2002) & (1) 1999 500 - (1) 1999 600
    1967 Buick Riviera (2)

  2. #2
    Join Date
    Jan 2005
    Location
    Japan
    Posts
    54,654
    My Cars
    11/88 E32 750iL+98 E36M3
    Is the heating system o.k.? Maybe a broken thermostat in open position. Had this some months ago on my E36 M3, replaced the thermostat and all fine again.
    But it could also be a coolant temperature sender, have to test. http://www.bimmerboard.com/forums/posts/1212512/
    read the complete thread there
    Last edited by shogun; 02-01-2018 at 10:11 AM.
    Shogun tricks and tips for the E32 series are HERE!

  3. #3
    Join Date
    Jan 2005
    Location
    Japan
    Posts
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    My Cars
    11/88 E32 750iL+98 E36M3
    Just to add one item to check: check the wiring to the temperature sender, these wires are pretty thin and can break, I once had a wire broken close to the sensor/plug.
    On the M70 there are 3 sensors at the back of the engine http://www.realoem.com/bmw/enUS/show...diagId=11_0785
    05 Temperature sensor, water 3-POL-2500-OHM 13621707366
    07 Temperature sensor, water M14X1,5 12621288158
    08 ENGINE COOLANT TEMP SENSOR 2-POL 12621710535

    copied from an info I posted 5 years ago:

    On the 750 M70 there are from right side to center
    ECT = engine coolant temperature sensor on M70 engine is at the right rear of engine in coolant cross pipe, 3-pins, That goes to the both DME, brown/red wire and ground to DME 1, brown/red/yellow wire and ground to DME 2.
    Testing data are in the Bentley repair Manual page 130-35

    left one >>temperature gauge sender
    right one>> engine coolant temperature (ECT) sensor (DME)
    middle one>>>EML coolant temperature sensor

    Location: in coolant crosspipe at rear of engine under the coolant expansion tank.

    The open circuit supply to the sensor is at a 5.0 volt reference level and this voltage reduces to a value that depends upon the resistance of the CTS resistance. Normal operating temperature is usually from 80° to 100° C.
    The ECU uses the CTS signal as a main correction factor when calculating ignition timing and injection duration. EML introduction http://www.europeantransmissions.com...MW/EML-BMW.pdf
    Shogun tricks and tips for the E32 series are HERE!

  4. #4
    Join Date
    Feb 2015
    Location
    Kuna, Idaho
    Posts
    736
    My Cars
    Too Many Cars (NOT!)
    shogun;

    Is there a way to get the coolant expansion tank out of the way to gain access to the sensors without having to drain the cooling system.

    Thank you
    Mike Drives:
    BMW's
    E24 - 635CSiA - (1) 1985 (US)
    E24 - 635CSi - (1) 1985 (EC)
    E31 - 850iA - (1) 1991 (Black)
    E31 - 850iA - (1) 1991 (Calypso Red)

    E32 - 740iA - (1) 1994
    E32 - 750iA - (1) 1990 (Not an "L") (EC German National)
    E32 - 735iL - (2) 1990
    E32 - 750iL - (1) 1990

    E38 - 740iLA - (2) (1) 1997 & (1) 1998
    E38 - 750iLA - (1) 1998
    E38 - 740iA - (1) 2000 "Short Sport"
    E39 - 528iA - (2) - 2000 & (1) 1997
    Also:
    2015 Ram 3500 Dually, Cumins 6.7, Std.Cab. Long box 4x4 (To haul all this junk when necessary)
    2014 Dodge Dart Rallye (Daily Driver)
    2007 Mercedes Benz CL600 (Brabus SV12S)
    Mercedes Benz SL's - (1) (2002) & (1) 1999 500 - (1) 1999 600
    1967 Buick Riviera (2)

  5. #5
    Join Date
    Jan 2005
    Location
    Japan
    Posts
    54,654
    My Cars
    11/88 E32 750iL+98 E36M3
    remove the plug from the coolant temperature sensor. Under the coolant cap there are 2 hoses connected left and right, 1 is the return line from radiator left side, the other the drain hose in case the cap opens when there is overpressure. Disconnect, the expansion tank is held by 2 10mm plastic nuts left and right outside.
    When all this is removed, there is only the bottom hose connected to the expansion tank. Lift the expansion tank on passenger side up and move it to a vertical position towards driver side, use a rope to keep it in that position, that should give you enough space. Otherwise you also have to disconnect the bottom hose, not too much coolant is lost, just the portion from the expansion tank, I then usually plug the thicker hose under the expansion tank when working there, so not more coolant is lost. Bleeding coolant afterwards is easy, just fill, run the engine, refill, M70 is self bleeding.
    Last edited by shogun; 02-12-2018 at 06:01 PM.
    Shogun tricks and tips for the E32 series are HERE!

  6. #6
    Join Date
    Feb 2015
    Location
    Kuna, Idaho
    Posts
    736
    My Cars
    Too Many Cars (NOT!)
    Interesting turn of events. Drove the car this morning just to verify weird temp reading and low and behold it was back to normal.

    Is it possible that having 356K kilometers on the odometer could mean "Old and Tired"?

    I'm just glad it's working correctly again, but I will keep a sharp eye on the temp.

    Thanks to all
    Mike Drives:
    BMW's
    E24 - 635CSiA - (1) 1985 (US)
    E24 - 635CSi - (1) 1985 (EC)
    E31 - 850iA - (1) 1991 (Black)
    E31 - 850iA - (1) 1991 (Calypso Red)

    E32 - 740iA - (1) 1994
    E32 - 750iA - (1) 1990 (Not an "L") (EC German National)
    E32 - 735iL - (2) 1990
    E32 - 750iL - (1) 1990

    E38 - 740iLA - (2) (1) 1997 & (1) 1998
    E38 - 750iLA - (1) 1998
    E38 - 740iA - (1) 2000 "Short Sport"
    E39 - 528iA - (2) - 2000 & (1) 1997
    Also:
    2015 Ram 3500 Dually, Cumins 6.7, Std.Cab. Long box 4x4 (To haul all this junk when necessary)
    2014 Dodge Dart Rallye (Daily Driver)
    2007 Mercedes Benz CL600 (Brabus SV12S)
    Mercedes Benz SL's - (1) (2002) & (1) 1999 500 - (1) 1999 600
    1967 Buick Riviera (2)

  7. #7
    Join Date
    Jan 2005
    Location
    Japan
    Posts
    54,654
    My Cars
    11/88 E32 750iL+98 E36M3
    In winter time sometimes funny thiongs happen which go away when it get's spring, summer...
    Maybe sooner or later you might have to change the capacitors in the cluster http://bmwe32.masscom.net/johan/dash...dash_caps.html
    Shogun tricks and tips for the E32 series are HERE!

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