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Thread: 750il runs too cold

  1. #1
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    750il runs too cold

    My 91 750 has had a problem where it pretty much stays in the blue on the temp gauge at all times. To start off I replaced the thermostat with a brand new oem one(85 C) but the issue remains.

    I feel the temp sensor isn’t bad because if I let the car idle long enough(20-30min) it’ll make its way up to half. But after about 8 min of driving at around 45mph it cools back down to the blue where it stays if I’m not sitting for an extended period of time.


    Any ideas what may be the cause. I feel my gas mileage and power is slightly less as I’m always in warm up temps. The car drives fine otherwise and has no check engine lights.

    Any help would greatly be appreciated. Thanks

  2. #2
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    In case the thermostat is fine, then check the visco fan clutch, this could be "locked" and always run on full speed, testing here http://www.mwrench.com/Whitepapers/FanClutchtest.pdf
    What about the aux fan? Is that running at high speed all the time? Should not. Testing here http://www.nmia.com/~dgnrg/page_20.htm

    Thermostat installed correct way? scroll down here http://bmwe32.masscom.net/sean750/wa.../waterpump.htm
    Some people somehow managed to install it the wrong way, the bimetal should be outside

    3 pin coolant temp sensor - 5V is reference value
    1. sensor coolant, on the back of the engine passenger side there are 3 coolant sensors. 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.

    Ohm at different temperatures http://www.e32-schrauber.de/bmw/s-tempsensor.htm

    Do you have a contactless thermometer to check the temperatures at various points.
    Last edited by shogun; 03-15-2019 at 04:52 AM.
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  3. #3
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    Thanks Shogun, I did test the fan that way and it seems to be working fine. After looking at those photos I’m sure I installed the thermostat the correct direction.

    I have a IR Temp gun so maybe I can use that to determine if the gauge is reading correct. I will do that first then update.

    In the instance that the gauge is not the issue is it possible I’m only running on 11 cylinders and not producing heat for operating temp?

    Thank you
    Last edited by shogun; 03-15-2019 at 05:43 PM.

  4. #4
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    I cannot imagine that 1 cylinder more or less makes such a difference.
    You could change the sensor, there you have to check for the correct part number in realoem, all 3 sensors have different part numbers.
    It could also be that the temperature gauge is defective. Here is such a case with a blown resistor for the speedo http://bimmerboard.com/forums/posts/467642/
    But that is all just guessing, first make a test with a IR temp gun to find out the real temperature.
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  5. #5
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    Just tested with the heat gun, it’s operating at about 80 degree Celsius on the upper coolant hose while the gauge stays in the blue. I will just replace all 3 sensors to be safe. Thanks for the help.
    Last edited by shogun; 03-21-2019 at 12:36 AM.

  6. #6
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    from center of engine bay towards e-box/fender
    5. Temperature sensor, water 13621707366 3-POL-2500-OHM
    7. Temperature sensor water 12621288158 M14X1,5
    8. Engine coolant sensor water 12621710535 2-pol
    http://bmwfans.info/parts-catalog/E3...ipe/#1710535_8
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  7. #7
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    Today I replaced all 3 temp sensors. Issue is still the same. The car will only get to half if sitting for atleast 30 min and goes back down as soon as I go over 40mph for a couple minutes. Aux fan is off, viscous fan is good, and after testing it seems the car is getting to temp. Thermostat housing was over 85 degrees even Though temp gauge is under 1/4. Any more ideas?
    Last edited by shogun; 03-21-2019 at 12:36 AM. Reason: unnecessary quote removed, pls use reply button instead of reply with quote

  8. #8
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    Maybe the problem is the thermostat, even if it is new. I would remove it and make a test with boiling water.
    Suere, that the thermostat is installed the correct way? Like this http://bmwe32.masscom.net/sean750/waterpump/Image68.jpg
    because the ETK shows the O-ring #2 in the wrong position! http://www.realoem.com/bmw/enUS/show...diagId=11_4604
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  9. #9
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    I will probably take it out and test it. I remember it being the correct direction because the peep whole on top lines up with the outdent in the casting. I should still double check though.
    Last edited by shogun; 03-21-2019 at 12:35 AM. Reason: unnecessary quote removed

  10. #10
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    also, if you have a spare cluster, use that one for a test, then you see if the cluster temp gauge might be a problem, but my guess is on the thermostat
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  11. #11
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    What’s weird is that it’s acting based off air flow. If I park the car after a drive it will be at half when I get back in after a 15-30 min break. Then as soon as I start driving again it’ll make its way back down after a couple minutes.
    Last edited by Jormotors; 03-21-2019 at 12:57 AM.

  12. #12
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    After drive and get back after 15 minutes, usually the temp goes up in engine bay ( our cars do not have a fan to cool the engine/drivetrain after engine has been switched off).
    Then when you start to drive. cool air goes thru the radiator and engine bay = temp goes down again.
    In idle, at red light, in traffic jam = not much air goes thru the radiator = temp goes up, when you start driving, airflow, temp goes down.
    As you describe it it, I assume the problem is an stuck open thermostat.
    Last edited by shogun; 03-21-2019 at 01:06 AM.
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  13. #13
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    Quote Originally Posted by shogun View Post
    After drive and get back after 15 minutes, usually the temp goes up in engine bay ( our cars do not have a fan to cool the engine/drivetrain after engine has been switched off).
    Then when you start to drive. cool air goes thru the radiator and engine bay = temp goes down again.
    In idle, at red light, in traffic jam = not much air goes thru the radiator = temp goes up, when you start driving, airflow, temp goes down.
    As you describe it it, I assume the problem is an stuck open thermostat.
    Yes, this is why I feel the gauge is correct. I’ll test that thermostat soon.

  14. #14
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    I dont think the t-state can be fitted wrong. I remember looking at mine and seeing that it would not fit correctly if flipped.

    Sounds like a fan issue to me. I would disable the electric fans first. Just unplug them at the sensor on the radiator. If that sensor is defective and kicking on too soon I could see the electric fans causing a drop also. And for the viscous, why not just remove it for now and see what happens? Remember, reverse thread! Helps to have the correct fan tool. 32mm maybe? I dont recall off-hand. Your electric fans will help prevent over-heating with the main fan gone.
    ______________________________
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  15. #15
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    I took the thermostat out again and put it in hot water. It opens and closes as normal. I didn’t originally see or hear the electric fan but I can unplug it and see what happens. My viscous fan is still off the car, I’ll switch it with my other 750il.

    - - - Updated - - -

    2A99CE9A-947B-4DE3-ABA0-C1C76B3AF5E6.jpg
    Last edited by Jormotors; 03-22-2019 at 03:59 PM.

  16. #16
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    Update: I tested or replaced everything related to the cooling system. One thing I have noticed is that sometimes when I floor it the car doesn’t want to accelerate. Rpms climb very slow and it only does It every once in a while. Not sure if it is related to running too cold but something just doesn’t feel right to me. The car never has a check engine light and only has 70k miles. Most of the time it feels fine and drives smooth.

  17. #17
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    Do you have someone which can read fault codes with a diagnostic tool? Not a Peake tool, must be better and can read more stored faults than the simple Peake.
    I would now check the wirings and plugs between the sensors and the Motronic and the cluster. These wires are very thin and can sometimes break, but still sometimes have enough contact.
    I assume you have connected the sensors with the correct plugs. Pls use the Bentley or the ETM and double check.
    The cluster gauge indication actually does not matter that much, that, that is just for info, but the sensors which supply the siganls to the Motronics and the EML control unit are important for engine management.
    A 1993 model has probably blue back cluster, and there the plug X16 yellow has 24 brown/yellow signal out=A and pin 26 signal in brown purple http://www.e32-schrauber.de/bmw/date...ung-x16-93.pdf

    On the EML control unit, here copied what I wrote 10 years ago on a German forum
    Anschlussbelegung EML Steuergerät M70 Motor Baujahr 1992

    Der Anschlussstecker EML hat die Bezeichnung X6004, Steckerbelegung

    Pin 1 EML Pedalwertgeber
    Pin 2 EML Pedalwertgeber
    Pin 3 frei
    Pin 4 ABS/ASC/ASC+T Steuergerät
    Pin 5 DME Steuergerät 1
    Pin 6 EML Pedalwertgeber / DME Steuergerät 1
    Pin 7 EML Pedalwertgeber
    Pin 8 Instrumentenkombi
    Pin 9 EML Pedalwertgeber
    Pin 10 EML Stellmotor 2
    Pin 11 EML Stellmotor 2
    Pin 12 EML Stellmotor 1
    Pin 13 RXD Datenleitung
    Pin 14 Masse
    Pin 15 EML Leuchte Instrumentenkombi
    Pin 16 EML Stellmotor 2
    Pin 17 EML Stellmotor 1
    Pin 18 Hauptrelais 2
    Pin 19 Masse
    Pin 20 EGS Steuergerät
    Pin 21 frei
    Pin 22 Steuergerät ABS/ASC/ASC+T
    Pin 23 Steuergerät ABS/ASC/ASC+T
    Pin 24 frei
    Pin 25 frei
    Pin 26 EML Stellmotor 1
    Pin 27 EML Stellmotor 1
    Pin 28 EML Stellmotor 2
    Pin 29 frei
    Pin 30 Masse
    Pin 31 Kühlwassertemperaturfühler = coolant water temperature feeler
    Pin 32 EML Pedalwertgeber/DME Steuergerät 2
    Pin 33 DME Steuergerät 2
    Pin 34 EML Stellmotor 2
    Pin 35 EML Stellmotor 1
    Pin 36 Hauptrelais 2
    Pin 37 Hauptrelais 2
    Pin 38 EML Stellmotor 1
    Pin 39 frei
    Pin 40 EML Stellmotor 2
    Pin 41 Klimaanlagenrelais
    Pin 42 Getriebewählschalter
    Pin 43 Schalter Geschwindigkeitsregelung
    Pin 44 Steuergerät Lock Sensor
    Pin 45 Kühlwassertemperaturfühler = coolant water temperature feeler
    Pin 46 EML Pedalwertgeber
    Pin 47 DME Steuergerät 1
    Pin 48 frei
    Pin 49 DME Steuergerät 1
    Pin 50 DME Steuergerät 2
    Pin 51 frei
    Pin 52 EGS Steuergerät
    Pin 53 ABS/ASC/ASC+T Steuergerät
    Pin 54 frei
    Pin 55 TXD Datenleitung
    [I][I]
    Next to the diagnosis port in engine bay there are the 2 main plugs, X20 and X21. X21 is next to the diagnosis port, then comes X20. X20 has on your 1993 model:
    11 Motor Temperaturfühler Pin 2 BR/GE ..........
    12 Motor Temperaturfühler Pin 1 .BR/VI...........


    on my 11/88 it is different:
    X20 .............................................X21
    1 D+ Lima .....................................1 Gas Pedal
    2 NC ............................................2 Gas Pedal
    3 Ökomat ......................................3 Gas Pedal
    4 Motor Tempfühler Pin 2 ................4 Gas Pedal
    5 Öldruckschalter ...........................5 Gas Pedal
    6 F28 Lambda-Heizung E-Box Fan ......6 Gaspedal DME II
    7 Klemme 15 f. DME I+II ..................7 NC
    8 DME I+II Wegfahrsperre ................8 NC
    9 DME-CC Drehzahlmesser ...............9 NC
    10 NC .........................................10 EML Bremslichtschalter
    11 NC .........................................11 NC
    12 DME Check Engine Lampe ...........12 Getriebe Prog. "S"
    13 Benzin Pumpe F23 .....................13 NC
    14 Tachosignal .............................14 NC
    15 12V Getriebe P+N .....................15 Gas Pedal DME I
    16 DATA RXD ...............................16 Taste Tempomat
    17 DATA TXD ...............................17 EML- Lampe
    18 Anlasser .................................18 EML- Lampe
    19 NC .........................................19 Taste Tempomat
    20 Motor Tempfühler Pin 1 ..............20 NC
    21 NC .........................................21 Benzin Pumpe F24 nach Sicherung
    22 NC .........................................22 NC
    23 NC .........................................23 NC
    24 NC .........................................24 NC
    25 NC .........................................25 NC

    The DME M1.7 352 pinout you can find in the ETM http://shark.armchair.mb.ca/~dave/BMW/e32/ look for coolant temperature feeler pins
    the older DME M1.2 like on my 11/88 750 has only 55 pins and there the pinout is here https://www.europeantransmissions.co...out1988_90.pdf
    your M1.7 has however 88 pins
    see pages 1367 a to c.


    EML light comes on when you switch ignition on and then goes off?
    Last edited by shogun; 03-24-2019 at 12:05 AM.
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  18. #18
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    Yes, eml light goes off. I have had a few cold mornings where it starts and triggers eml but after restarting it goes away. Only has happened 2 or 3 times but not recently.

    Thanks for all the info Shogun! I’ll look into testing things one by one. This car is a mint example so I hope to correct every issue with it.

  19. #19
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    Rfi

    Quote Originally Posted by Jormotors View Post
    Update: I tested or replaced everything related to the cooling system. One thing I have noticed is that sometimes when I floor it the car doesn’t want to accelerate. Rpms climb very slow and it only does It every once in a while. Not sure if it is related to running too cold but something just doesn’t feel right to me. The car never has a check engine light and only has 70k miles. Most of the time it feels fine and drives smooth.

    I’m having the exact same problem right now on my 1993 740iL
    I know this post is years old but if you ever found out the exact problem with it some info would be great, currently still stuck trying to figure it out

  20. #20
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    Make a stomp test to see if there are any fault
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  21. #21
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    Quote Originally Posted by shogun View Post
    Make a stomp test to see if there are any fault
    The stomp test isn’t working on my e32, I’ve tried it while it has the engine light on as well and still no success,

  22. #22
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  23. #23
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    Quote Originally Posted by shogun View Post
    Okay I’ve been trying it again and still no success, all my lights are on while my keys turned just before starting the engine, once started they all go away, but the stomp test isn’t working, and It confuses me as to why my engine would be cooling off even when it’s about 50 degrees Fahrenheit outside going no faster than 40mph

    - - - Updated - - -

    Quote Originally Posted by shogun View Post
    Okay I’ve been trying it again and still no success, all my lights are on while my keys turned just before starting the engine, once started they all go away, but the stomp test isn’t working, and It confuses me as to why my engine would be cooling off even when it’s about 50 degrees Fahrenheit outside going no faster than 40mph

  24. #24
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    Try to find a shop near your home which can read on these E32 models fault codes. Or another older BMW owner with the necessary software and laptop nearby? Local BMW car club where you can ask? Your 1993 740 has already a newer generation DME where one can read more fault codes than on my old M70 M1.2 DME.
    What did you check so far?
    Did you make a smoke test for air leaks in intake system?
    Tested the MAF, checked spark plugs, fuel pump pressure, fuel volume, etc pp?
    Shogun tricks and tips for the E32 series are HERE!

  25. #25
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    Quote Originally Posted by shogun View Post
    Try to find a shop near your home which can read on these E32 models fault codes. Or another older BMW owner with the necessary software and laptop nearby? Local BMW car club where you can ask? Your 1993 740 has already a newer generation DME where one can read more fault codes than on my old M70 M1.2 DME.
    What did you check so far?
    Did you make a smoke test for air leaks in intake system?
    Tested the MAF, checked spark plugs, fuel pump pressure, fuel volume, etc pp?
    Haven’t checks the MAF getting new spark plugs and I’m replacing the filters to my fuel pump so I’ll check pressure and volume then, thank you for your helpful insight!

    - - - Updated - - -

    Quote Originally Posted by shogun View Post
    Try to find a shop near your home which can read on these E32 models fault codes. Or another older BMW owner with the necessary software and laptop nearby? Local BMW car club where you can ask? Your 1993 740 has already a newer generation DME where one can read more fault codes than on my old M70 M1.2 DME.
    What did you check so far?
    Did you make a smoke test for air leaks in intake system?
    Tested the MAF, checked spark plugs, fuel pump pressure, fuel volume, etc pp?
    Haven’t checks the MAF getting new spark plugs and I’m replacing the filters to my fuel pump so I’ll check pressure and volume then, thank you for your helpful insight!

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