Why don't modern engines use a thermocouple (electronic temperature sensor) instead of a (wax element) thermostat?

  • 1
    This question reminds me of the ones like "why don't cars use cameras instead of a rear view mirror". Some things just work and work very well even tho the tech might seem dated.
    – JPhi1618
    Commented Apr 22, 2016 at 12:55
  • @JPhi1618 I see your correlation. It's not really the same thing though.
    – voices
    Commented Apr 23, 2016 at 2:48

1 Answer 1


A thermocouple merely generates voltage according to the temperature, while an automotive thermostat is basically an autonomous temperature sensitive coolant valve. You can't replace a thermostat with a thermocouple because their functions are completely different. You could replace a coolant sensor with a thermocouple, but resistive sensors are more convenient to use in this case.

  • I think the OP is asking about the prevalence of wax-element thermostats as opposed to electric thermostats
    – Zaid
    Commented Apr 22, 2016 at 9:50
  • @Zaid Might be, but it doesn't have much to do with thermocouples. I'll update the answer when it becomes more clear. Commented Apr 22, 2016 at 9:56
  • @IhavenoideawhatI'mdoing Good answer; but of course, a thermocouple could actuate a variable response from a separate component (coolant valve).
    – voices
    Commented Apr 23, 2016 at 3:03
  • @Zaid Not quite, I got the idea when troubleshooting a gas hot water heater (yes, even though it had an (electric/electronic?) thermostat as well).. but do feel free to expand on your idea, if you like. It's quite relevant.
    – voices
    Commented Apr 23, 2016 at 3:11
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    @tjt263 Oh, the point is that the switch would be controlled directly by the thermocouple? In that case you're right, it's doable, but not cheaper or more reliable than the good ol' wax thermostat. Commented May 9, 2016 at 6:54

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