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Thread: Temperature shut off

  1. #1
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    Temperature shut off

    Has anyone ever or is it possible(maybe with a raspberry pi or Arduino) to make a temperature controlled auto shut off. For the life if me I can't remember what would be the danger zone but for some reason 210-220 is gettin there. So say soon as the engine hits 220 the engine goes into auto shut down,electric fan on. Obviously there would have to be safety measures thought of but I think it would be cool to make the engine itself be able to essentially say "whoa" bro,if I dont stop NOW I'm done

  2. #2
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    In case you have that problem, then there is something wrong with your cooling system. Normally one should never come into such situation, if the cooling system including water pump, thermostat, radiator and aux fan stage 1 and 2 work properly.
    But even 210-220 F is not that extreme high http://www.nmia.com/~dgnrg/tempgage.htm

    The driver has a temperature gauge in front of him in the cluster. He should be clever enough to see that. Besides that, manual says in section Indicator and warning lamps
    Red
    Indicator lamp comes on, the warning "COOLANT TEMPERATURE" appears in Check Control*: engine overheated. Switch off the engine immediately and allow it to cool down.
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  3. #3
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    it would be easiest to use a dedicated switch that triggers a relay that breaks contact with some power or ground essential to keep the engine running. But if you are smart, unlike me, you could figure out how to read the factory temp sender and use some trigger for a point along its scale along with a device to read it that has an output. But rather than abruptly shut the car down on the highway or some place where sudden loss of power steering and power could be dangerous, maybe you could have it trigger an audible alarm so you can safely shut the car down.

  4. #4
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    the question i'd ask myself is, is it smart to shut uf such a hot engine. If the water pump failed there's no sense in letting it run in idle, but if the cooling system still works, i'd prefer letting it idle to cool down instead of shutting it right off. So maybe a warning light or similar to inform you about the temperature (which is already installed from factory) is better, that will still give you some time to determine what to do. i think an engine shutting off on it's own is dangerous.
    Last edited by samy01; 01-20-2020 at 10:23 AM.

  5. #5
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    For every pound of pressure on the coolant system you get an additional 1.5 degrees so since water boils at 212 you can see that importance of no leaks in the coolant system, your switching would have to be higher because we are running at 220 normally, ive seen recorded temperatures in dmes for e39 s when the have over heated at 286 and these engines did not wreck the Head gasket, but your getting close.

  6. #6
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    Quote Originally Posted by jclausen View Post
    For every pound of pressure on the coolant system you get an additional 1.5 degrees so since water boils at 212 you can see that importance of no leaks in the coolant system, your switching would have to be higher because we are running at 220 normally, ive seen recorded temperatures in dmes for e39 s when the have over heated at 286 and these engines did not wreck the Head gasket, but your getting close.
    Right I said I was just using 220 as a for instance and really didn't know

  7. #7
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    People have to realize that monitoring the water temp is not going to save you from overheating. We overheat because we've lost coolant and there is an air pocket. The temp of the head has to be monitored, the actual aluminum.

    So, one would have to hookup a probe at one or more sites on the head and record data, find out how hot it gets when driving normal and when it's being driven really hard. Since water is keeping it cool its not going to go too far above what the thermostat is set to.

    When the over temp idiot light goes on, it's typically too late.
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  8. #8
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    The gauge will stay centered up to around 218 before it starts to budge, that's why our gauges are so misleading. The sending unit will read even in an air pocket because it will be steam which is very effective at conducting heat, there is also the thermal transfer from the aluminum cylinder head, so your gauge will respond but doesn't give much warning due to the non-linear gauge.

    - - - Updated - - -

    Read your real time numbers through an obdII reader for an eye opener, the temperature fluctuates far more than the gauge would lead you to believe.

  9. #9
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    The engine already shuts off when it gets too hot. You can wonder if it waits too long to turn off, but it does turn off. And, you can start it again after it cools .

  10. #10
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    Do you know what temperature that is for an OBD2 E36M3?

  11. #11
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    Quote Originally Posted by pbonsalb View Post
    Do you know what temperature that is for an OBD2 E36M3?
    Right after the red light comes on.

  12. #12
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    The engine already shuts off when it gets too hot
    that is new to me that the engine shuts off, even my E32 750 from 11/88 does not have that function, maybe newer cars. Can we see that from the wiring diagrams? There is a double temperature switch 13621703993 on the cylinder head, 1 signal goes to the cluster, is processed inside the cluster and shown on the gauge, and the other signal I can see as input to the DME on pin 10 on the 1997 wiring diagram, and that signal is used for the engine management for fuel injection
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  13. #13
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    My thoughts are if the cooling system is still intact and full of coolant maybe the shut down should stop the engine but leave the electric fan running. If the coolant isn't isn't being pumped it will still circulate naturally by convection if there is some cooling effect by the fan.

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  14. #14
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    You wouldnt want that to happen.. Safety first. Better to have an overheat engine where you can pull off and have a overheated engine rather than a suddenly shut off engine going 80mph on the highway and now no power brakes or power steering. Thats much more DANGEROUS than just having a blown headgasket. Potentially much more expensive +death. Lol

  15. #15
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    yes that's definitely not intened by BMW to have the engine shut off at high temperatures, there must be something else going on

  16. #16
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    checked it in the DME specification for M1.1, M1.3, which I have, other DME's function the same way. The DME will just take substitute values..
    Limited Operating Strategy (LOS)
    In the event of a serious fault in one or more of the sensors or their wiring circuits, Motronic will substitute a fixed default value in place of the defective sensor. This procedure is often termed limp home. A serious fault occurs when the signal from the sensor is outside of its normal operating parameters. When operating in LOS the engine may actually run quite well with failure of one or more minor sensors. Since the substituted values are those of a hot engine, cold starting and running during the warm-up period may be less than satisfactory. Also, failure of a major sensor, ie the AFS, will tend to make driving conditions less easy. Once the fault has cleared, Motronic will once more accept the live signal from the sensor. The following LOS measures are taken in the event of a failure.
    Component..............................Action
    AFS........................substitute values are calculated from the TS position. The load signal is fixed to 6.0 ms and the ignition timing to 20 BTDC once the TS contact is open.
    ATS........................substitute value of 50 C . A code will not be set, and LOS will not commence until a minimum of 3 minutes after engine start and the engine idling for a minimum of 30 seconds.
    CID sensor.............injectors are pulsed simultaneously
    CO pot..................substitute value of 2.77 volts
    CTS...................substitute value of 80 C if ATS value is greater than 20 . if ATS value is less than 20 , substitute value of ATS value for first three minutes after engine start-up.
    OS.....................substitute value, open loop control
    TS.....................substitute values, restricted engine operation

    CTS
    The CTS is immersed in the coolant system and contains a variable resistance that operates on the NTC principle. When the engine is cold, the resistance is quite high. Once the engine is started and begins to warm-up, the coolant becomes hotter and this causes a change in the CTS resistance. As the CTS becomes hotter, the resistance of the CTS reduces (NTC principle) and this returns a variable voltage signal to the ECU based upon the coolant temperature. 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.

    ATS
    The ATS is mounted in the AFS inlet tract and measures the air temperature before it enters the inlet manifold. Because the density of air varies in inverse proportion to the temperature, the ATS signal allows more accurate assessment of the volume of air entering the engine. However, the ATS has only a minor correcting effect on ECU output. The open circuit supply to the sensor is at a 5.0 volt reference level and the earth path is through the AFS earth return circuit. The ATS operates on the NTC principle. A variable voltage signal is returned to the ECU based upon the air temperature. This signal is approximately 2.0 to 3.0 volts at an ambient temperature of 20 C and reduces to about 1.5 volt as the temperature rises to around 40 C.
    Last edited by shogun; 01-24-2020 at 08:30 PM.
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  17. #17
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    Shogun overkilled it.. Best way would be to have an after market temp sensor installed, hooked to a controller that turns of the dme relay power when temp gets up..

    - - - Updated - - -

    Its still a horribly dangeroues and stupid thing to do.. Not just for the loss of power steering amd brakes... If an engine is overheating. Turning it off also keeps the engine from cooling itself with the cooling system and thus retains all the heat. The only way around an overheat is to have a proper working cooling system.

  18. #18
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    Okay, in my early days of owning a BMW 3 Series, the radiator top hose snapped off on a mountain road at night time. I stopped and filled up with more water and made a roadside repair to the hose that did not hold very well. I got underway and made it to the summit of the roadway at the same moment that the engine shut off because the needle was pegged and the red light came on. I rode deadstick down the mountain about 10 miles to the parking lot where I could call the tow truck to come get me. This was before there was cell service, and the roadway where the car broke was not wide enough for a tow truck and my car, and the normal traffic. The point is, the car knows that it is hot and it shuts off in a feeble attempt to not kill itself because the idiot working the controls does not pay attention to the lights and instruments. (I was paying attention, but I just needed those final 100 yards up the hill to make to where I could coast to the bottom.) Power steering and brakes are nice to have, but there's absolutely no reason to think that the car cannot be managed without power. I imagine this is the event that cracked the head in my car, and it took several months to find out that the head was having any trouble at all.

  19. #19
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    your head cracked, and due to the high temperatures leading to massive pressure in the cooling system it pushed water through the crack into the combustion chamber, that's why it shut off.

    The ECU isn't intended by BMW to shut off the engine.
    Last edited by samy01; 01-26-2020 at 01:34 AM.

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