What part regulates the flow of coolant to maintain optimal engine temperature?

The thermostat is the component that regulates the flow of coolant to maintain the engine's optimal temperature. When the engine starts and is cold, the thermostat remains closed, preventing coolant from flowing to the radiator. This allows the engine to heat up quickly to its operating temperature. Once the engine reaches the predetermined temperature, the thermostat opens, allowing coolant to flow to the radiator where it can dissipate heat. This regulation ensures that the engine operates efficiently and prevents overheating or running too cool, both of which can lead to reduced performance or engine damage.

The water pump circulates coolant through the engine and radiator but does not control the temperature directly; its role is to move the coolant. The radiator is responsible for dissipating heat from the coolant, and the coolant reservoir holds excess coolant but does not regulate flow or temperature. Hence, the thermostat plays a crucial role in maintaining the desired temperature of the engine.