FAA Powerplant Written Practice Test

Which factor is important in determining the proper grade of oil for a specific engine?

1. Operating speeds of bearings

2. Color of the oil

3. Cost of the oil

4. Brand reputation

The correct answer is: Operating speeds of bearings

The proper grade of oil for a specific engine is primarily determined by the operating speeds of the bearings, as this directly influences the oil's ability to maintain a sufficient film thickness to protect the engine components under various operating conditions. In high-speed applications, the oil must possess specific properties that allow it to maintain its viscosity and ensure effective lubrication at elevated temperatures and shear rates. For instance, multi-viscosity oils are often recommended for engines that operate across a range of temperatures and speeds, ensuring the oil remains effective in providing lubrication under both low- and high-load situations. While factors like the color of the oil, cost, and brand reputation may influence a consumer's choice, they do not have a direct impact on the functional performance of the oil in relation to the engine’s operational requirements. Thus, the most critical consideration for selecting the appropriate oil is its compatibility with the engine's design and operating conditions, particularly related to the speeds and tolerances of its bearings.