A car thermostat and a home thermostat differ in their function and design. A car thermostat is designed to regulate the flow of coolant through the engine to maintain a consistent temperature, while a home thermostat is designed to regulate the temperature of the air in a room. Car thermostats are typically made of brass or stainless steel, while home thermostats are made of plastic or metal. Additionally, car thermostats are controlled by the engine, while home thermostats are controlled by a thermostat unit.