What does "residual oil" refer to?

Residual oil refers to the oil that remains in the tanks after draining. In aviation maintenance, it is important to ensure that all oil is adequately drained from systems to prevent contamination and ensure optimal operation of engines and equipment. The term "residual" implies that some amount of oil is left behind, often due to the design of the system or the difficulty in completely evacuating all fluids. Understanding residual oil is crucial for maintenance practices as it can affect the performance and longevity of the equipment. This concept also emphasizes the importance of performing thorough inspections and maintenance to manage oil levels and ensure system integrity.