FAA Powerplant Written Practice Test

What is the primary reason for changing aircraft engine lubricating oils at specified intervals?

1. The oil improves performance over time

2. The oil contains moisture, acids, and suspended particles

3. The oil loses all viscosity

4. The oil is exposed to high temperatures

The correct answer is: The oil contains moisture, acids, and suspended particles

The primary reason for changing aircraft engine lubricating oils at specified intervals is the accumulation of moisture, acids, and suspended particles in the oil over time. As the oil circulates through the engine, it picks up contaminants such as microscopic metal particles from engine wear, combustion byproducts, and moisture that can condense within the engine. These contaminants can degrade the performance of the oil, leading to increased engine wear, reduced lubrication quality, and potential engine damage. Maintaining proper lubrication is crucial to ensure that moving parts within the engine are protected and to prevent issues such as corrosion and sludge buildup, which can affect engine efficiency and reliability. Regular oil changes help prevent these problems by removing contaminated oil and replacing it with fresh oil, ensuring that the engine operates smoothly and efficiently. While factors like oil viscosity and exposure to high temperatures can impact oil performance, the main concern driving the need for regular oil changes is the degradation due to contaminants. Thus, recognizing the buildup of harmful substances emphasizes the importance of adhering to recommended oil change intervals to maintain engine health and performance.