12 volt automotive engine over heat warning and shut down circuit

Discussion in 'General Electronics Chat' started by bluecar5556, Mar 2, 2015.

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  1. bluecar5556

    Thread Starter New Member

    Jun 9, 2010
    Hello allaboutcircuits members,

    I just recently overheated the engine on my car to the point of blowing the head gasket. Being more mechanically inclined then building electrical circuits, i'm asking for help creating a 12 volt automotive engine over heat warning and shut down circuit using a 555 timer with two temperature thresholds. During the first over heat threshold, the circuit will sound a piezo buzzer preferably at 4 Khz and blink an LED. If the warning is not heard over loud music or otherwise and the engine is allowed to over heat a few degrees more to the second threshold, a fail safe shut down circuit will engage, disabling the engine from over heating further.

    Instead of utilizing the vehicles engine coolant instrument cluster gauge or ECM/ECU/PCM NTC temperature thermistor, i'd rather use a standalone NTC thermistor attached to a bolt, on the head of the engine, via a ring terminal so it will be universal from one vehicle to the next. This way it will be a foolproof design as some vehicles have the engine coolant thermistors up high and ineffective during low coolant situations, exposing them to air and giving a false low reading.

    The shut down circuit may use a 30A SPST mechanical relay with snubber diode, as I believe the circuit and parts list should be as simple as possible so others can easily make it for their own personal use.

    Ignition shut down relay:
    (NC) 30 & 87A will complete the vehicles primary ignition circuit under normal engine temperatures
    (NO) 30 & 87 will disengage the ignition circuit during over heat engine temperatures.

    Disclaimer: Shutting down an engine can be dangerous in certain instances and the circuit should be used with caution. Perhaps a switch should be within reach of the driver, applying 12V to 87A of relay when turned on.
  2. bwilliams60

    Active Member

    Nov 18, 2012
    You are going to find this thread gets shut down quite quickly and your last line explains why. You cannot shut down a vehicle in the middle of a busy highway and hope for a good outcome. If it were that simple, engineers would have done it a long time ago. I am an automotive and Truck and Coach technician and Professor and although I see where you feel there is a need for this, I also think that people need to pay more attention to their vehicles. There are warning lights and gauges that warn drivers of potential problems and regular maintenance should avert any potential problems. If people choose to ignore them or not maintain their vehicles, sorry about their luck. I don't mean to sound cold, but changing the system design and endangering lives is not the answer. The truck world has found a safe way to shut down engines but gives you enough time to get off the road if need be. Unfortunately, gas engines heat up faster and bad things happen when there is no coolant. Good luck with your endeavor.
  3. bertus


    Apr 5, 2008

    I am closing this thread as it violates AAC policy and/or safety issues.

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