What part is responsible for controlling coolant flow in a vehicle?

The correct answer is the thermostat, which plays a critical role in regulating the engine's temperature. The thermostat is essentially a valve that opens and closes based on the coolant temperature, enabling it to control the flow of coolant between the engine and the radiator.

When the engine is cold, the thermostat remains closed, preventing coolant from circulating, which allows the engine to reach its optimal operating temperature quickly. Once the desired temperature is achieved, the thermostat opens, allowing hot coolant to flow to the radiator, where it is cooled before returning to the engine. This cycle helps maintain the engine at a safe and efficient temperature, preventing overheating and improving performance.

While the water pump is involved in the overall circulation of coolant, it does not have the ability to control the flow. The pump forces coolant through the system, but it's the thermostat's function to manage the flow based on temperature. The oil filter and fuel pump are components that serve different functions unrelated to coolant flow.