Certified Flight Instructor - Flight Instructor Airplane Practice Exam

How is coolant circulated in a liquid cooled engine?

1. An electric pump

2. An engine driven pump

3. Capillary attraction

4. A mechanical pump

The correct answer is: An engine driven pump

In a liquid-cooled engine, coolant circulation is primarily achieved through an engine-driven pump. This type of pump is typically mounted directly on the engine and is mechanically connected to the engine's crankshaft. As the engine runs, the crankshaft drives the pump, which forces the coolant through the engine block, absorbing heat, and then across the radiator where it releases that heat to the atmosphere. The efficiency of an engine-driven pump is crucial for maintaining optimal engine temperatures, preventing overheating, and ensuring smooth operation. This system allows for consistent and reliable cooling, which is essential for preserving the engine’s performance and longevity. While other methods such as an electric pump could work for circulating coolant, they are not the conventional choice for standard aviation engines. Capillary attraction is not applicable in engine cooling systems, as it cannot circulate significant volumes of liquid effectively. Mechanical pumps are a broad category that can refer to either engine-driven or electric pumps but typically implies a manual or external mechanism, which isn't the standard method employed in most liquid-cooled aircraft engines.