What is the primary function of engine oil in aircraft engines?

• A. Dampening noise within the gearbox.
• B. Lubrication, cooling, sealing, and cleaning.
• C. Fuel metering and combustion control.
• D. Absorbing vibration from the propeller.

Answer: (B)

Engine oil’s main job is to keep the engine’s moving parts working smoothly by four intertwined roles: lubrication, cooling, sealing, and cleaning. The lubricating film it forms between bearings and gears dramatically reduces friction and wear, which prolongs component life. As oil circulates, it carries heat away from hot surfaces to an oil cooler, helping control temperatures. The oil also seals small gaps between rotating or sliding surfaces, reducing oil leaks and helping maintain proper clearances. Finally, it cleans by suspending dirt, metal particles, and combustion byproducts and carrying them to filters, protecting surfaces from deposits and corrosion. While oil can influence noise or vibration to some extent, those are not its primary functions—the four roles above are the core purpose. The other options describe functions belonging to the fuel system or structural aspects, not the engine oil itself.