Which factor directly affects the efficiency of a marine engine?

Fuel quality directly affects the efficiency of a marine engine because it influences how effectively the engine can convert fuel into mechanical energy. High-quality fuel ensures optimal combustion, which leads to more power generated from the same amount of fuel, reduced emissions, and smoother engine operation. Impurities or poor fuel quality can result in incomplete combustion, leading to decreased efficiency, increased fuel consumption, and potential engine damage over time.

While engine age can affect performance and efficiency, it does not directly impact the efficiency level in the same way that the fuel burned does. The weight of the vessel impacts the energy required for propulsion but does not affect the inherent efficiency of the engine itself. The design of the cooling system is crucial for maintaining operational temperatures but is more concerned with reliability rather than direct efficiency in fuel conversion. Therefore, fuel quality is the most pivotal factor when considering marine engine efficiency.