Speaker 1: Welcome to brain Stuff from how stuff Works dot com
Speaker 1: where smart Happens. Hi. I'm Marshall Brain with today's question.
Speaker 1: How does the thermostat in a car's cooling system work?
Speaker 1: Any liquid cooled car engine has a small device called
Speaker 1: the thermostat that sits between the engine and the radiator.
Speaker 1: The thermostat and most cars, is about two inches in diameter.
Speaker 1: Its job is to block the flow of coolant to
Speaker 1: the radiator until the engine is warmed up. When the
Speaker 1: engine is cold, no coolant flows to the radiator. Once
Speaker 1: the engine reaches its operating temperature, which is usually about
Speaker 1: two degrees fahrenheit, the thermostat opens by letting the engine
Speaker 1: warm up as quickly as possible. The thermostat reduces where
Speaker 1: deposits and emissions. If you ever have the chance to
Speaker 1: test the thermostat, it's an amazing thing to watch because
Speaker 1: what they do seems impossible. You can put one in
Speaker 1: a pot of boiling water on the stove. As it
Speaker 1: heats up, its valve opens more than an inch. Apparently
Speaker 1: I magic. If you'd like to try it yourself, go
Speaker 1: to a car part store and buy one for a
Speaker 1: couple of bucks. The secret of the thermostat lies in
Speaker 1: the small cylinder located on the engine side of the device.
Speaker 1: This cylinder is filled with a wax that begins to
Speaker 1: melt at about a hundred eighty degrees fahrenheit. Different thermostats
Speaker 1: open at different temperatures, but a hundred eighty degrees is
Speaker 1: a common temperature for a thermostat. To open it, a
Speaker 1: rod connected to the valve presses into this wax. When
Speaker 1: the wax melts, it expands significantly and pushes the rod
Speaker 1: out of the cylinder, opening the valve. The wax expands
Speaker 1: so much because it's changing from a solid to a
Speaker 1: liquid in addition to expanding from the heat. This same
Speaker 1: technique is used in automatic openers for greenhouse vents and skylights.
Speaker 1: In these devices, the wax melts at a much lower temperature.
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