The thermostat in an automobile is like a doorway from the radiator into the engine. Water cannot pass into the engine to cool it until the thermostat opens up and creates a passage. The thermostat opens at a predetermined temperature.
The function of a thermostat is to allow an automobile's engine to heat up rapidly, only allowing coolant in when the temperature gets hot enough. They are generally located at the base of the top radiator hose, but in some newer applications, they can be in other places, as well. There is a valve in thermostats that opens up at a given temperature, letting in coolant from the radiator so the engine does not overheat.
The different types of automobile thermostats will generally refer to the predetermined temperature in which they are set to open. Once 180 degree F thermostats were the most popular, but now manufacturers are recommending 190 or 195 degree F models so that the engine reaches optimum operating temperature in a short period of time. Some race applications use a 160 degree F model so that high-horsepower motors do not overheat quickly and burn up.
Automobile thermostats feature a chassis, valve and small ball of wax in the middle of it all. The chassis, or body, of the thermostat is made of a corrosive-resistant compound that will withstand years of being subjected to high heat and moisture conditions. When the water in the radiator reaches operating temperature, the small ball of wax begins to melt, allowing the valve to open and water to pass through.
The size of the thermostat will normally be directionally proportional to the size of the engine in the car. Most are approximately 2 inches across, but some very small cars require much smaller thermostats. The bolts used to hold the thermostat in place are generally 10 mm, and the size of the gasket used must match the size of the mating surface on the thermostat exactly.
Many car-enthusiasts believe that completely removing the thermostat is perfectly acceptable, because their engine does not overheat. This is not a good idea, because it will take much longer for the engine to reach operating temperature, where it best burns fuels and emits the least amount of smog-causing chemicals into the ozone. Also, the vehicle's heater works directly from the coolant temperature, and if it is too low, you may experience cold air coming from the heater all winter.
