The normal operating temperature of a modern engine is between 194°F (90°C) and 221°F (105°C). The job of a thermostat is to help the engine warm up faster and maintain the engine temperature above the minimum operating temperature (194°F or 90°C).
A conventional thermostat is a simple temperature-controlled two-way valve that opens at a specified temperature.
In most cars, a thermostat is installed on the engine and is connected to the upper or lower radiator hose.
How a thermostat works:
When the engine is started cold, the thermostat (the main valve) is closed; there is no flow through the radiator. The smaller by-pass valve is open and the coolant circulates only within the engine and through the vehicle heating system,
As the engine warms up closer to the operating temperature, the thermostat gradually opens up, allowing coolant flow through the radiator.
In cold weather, if the engine temperature drops close to the lower limit of the operating range (194°F or 90°C), the thermostat closes again.
