Coolant sensor

No. I want a sensor that when the coolant is cold it will be on and when the engine warms it will turn off. I want to use a solenoid on my carb so when the engine is cold it will hold the high idle and when the engine warms up it will release the solenoid.
I dont have a choke so this is how I am trying to warm up the engine.
I hope you can follow me on this.
Opposite of what a sensor does for an electric fan.