Removing the thermostat from a vehicle causes the engine to operate at a cooler temperature than its design. While this prevents overheating, it also increases fuel consumption, the viscosity of motor oil and engine wear. If the ambient temperatures are cold, the vehicle's heating system sometimes does not provide enough heat to warm passengers or defrost windows in a timely manner.
Automobile thermostats have a small cylinder filled with wax on the engine side of the device. Manufacturers select this wax to melt at approximately 180 degrees. The melting wax expands, pressing a rod from the cylinder to open a valve. When the valve is open, coolant flows to the radiator for cooling. When it is closed, coolant bypasses the radiator and goes directly to the water pump where it recirculates through the engine.
Coolant pumped through the radiator cools due to air forced through its fins as the car travels forward. When the vehicle slows, a fan pulls additional air through the radiator to maintain the correct operating temperature.
Activating the heater inside the vehicle opens a valve to allow coolant to pass through a radiator located inside the vehicle, which is the heater core. A small electric fan pulls air from the cabin of the vehicle through the heater core, where it warms to maintain the temperature inside the car.