WEBVTT - How Car Thermostats Work

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<v Speaker 1>Welcome to brain Stuff from how stuff Works dot com

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<v Speaker 1>where smart Happens. Hi. I'm Marshall Brain with today's question.

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<v Speaker 1>How does the thermostat in a car's cooling system work?

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<v Speaker 1>Any liquid cooled car engine has a small device called

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<v Speaker 1>the thermostat that sits between the engine and the radiator.

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<v Speaker 1>The thermostat and most cars, is about two inches in diameter.

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<v Speaker 1>Its job is to block the flow of coolant to

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<v Speaker 1>the radiator until the engine is warmed up. When the

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<v Speaker 1>engine is cold, no coolant flows to the radiator. Once

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<v Speaker 1>the engine reaches its operating temperature, which is usually about

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<v Speaker 1>two degrees fahrenheit, the thermostat opens by letting the engine

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<v Speaker 1>warm up as quickly as possible. The thermostat reduces where

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<v Speaker 1>deposits and emissions. If you ever have the chance to

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<v Speaker 1>test the thermostat, it's an amazing thing to watch because

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<v Speaker 1>what they do seems impossible. You can put one in

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<v Speaker 1>a pot of boiling water on the stove. As it

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<v Speaker 1>heats up, its valve opens more than an inch. Apparently

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<v Speaker 1>I magic. If you'd like to try it yourself, go

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<v Speaker 1>to a car part store and buy one for a

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<v Speaker 1>couple of bucks. The secret of the thermostat lies in

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<v Speaker 1>the small cylinder located on the engine side of the device.

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<v Speaker 1>This cylinder is filled with a wax that begins to

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<v Speaker 1>melt at about a hundred eighty degrees fahrenheit. Different thermostats

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<v Speaker 1>open at different temperatures, but a hundred eighty degrees is

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<v Speaker 1>a common temperature for a thermostat. To open it, a

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<v Speaker 1>rod connected to the valve presses into this wax. When

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<v Speaker 1>the wax melts, it expands significantly and pushes the rod

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<v Speaker 1>out of the cylinder, opening the valve. The wax expands

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<v Speaker 1>so much because it's changing from a solid to a

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<v Speaker 1>liquid in addition to expanding from the heat. This same

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<v Speaker 1>technique is used in automatic openers for greenhouse vents and skylights.

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<v Speaker 1>In these devices, the wax melts at a much lower temperature.

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