Whether mineral-based, synthetic blend, straight grade, or multigrade, all aviation oils are compatible and can be mixed without harm to the engine. Procedure 1: Answer the following multi-choice questions concerning aircraft lubricants. 1. High viscosity oils tend to flow: a. Freely. b. Slowly. c. Extremely fast. 2. What is the SAE for straight mineral oil utilized in the Beech-95 if the average ambient temperature is between -17.78 C to 21.11.C? a. SAE 40 b. SAE 30 C. SAE 20 3. When proper servicing equipment is available, aircraft components will be serviced through an oil servicing. unit. If this equipment is not available and cans are used, these cans will be thoroughly cleaned prior to each ser- vicing to prevent contamination. Thoroughly agitate the oil in the can prior to adding oil to the system either at an oil. Synthetic and mineral based oils: a. Can be mixed by a certificated A&P mechanic. b. May not be mixed by a certificated A&P mechanic. c. May only be mixed by flight line service personnel. Not a problem: All aviation piston engine oils are compatible,” Silveira said. “Whether mineral-based, synthetic blend, straight grade or multigrade, all aviation oils are compatible and can be mixed without harm to the engine.” Aircraft operators are required by § 91.9 to only use fuels and oils listed in the AFM or RFM. These fuels and oils must, therefore, be identified with sufficient specificity to ensure that the engine and aircraft continue to meet their airworthiness certification basis during service. Most non-aviation greases usually mix well with others, but you may need to separate them by usage. For example, I have a separate grease gun that I only use for lubricating snow mobiles because it has very good low-temperature properties. This AC provides acceptable methods, but not the only methods, that may be used to approve aircraft, engines, or APUs to operate with specified propulsion fuels and lubricating oils. Except as a temporary measure in an emergency, different oils should not be mixed. Consistent indiscriminate mixing of oils may create high oil-consumption problems or clogged oil control rings and oil screens. Oil consumption is a very important engine health trend to monitor. In this article, we'll cover what MIL-SPEC standards are, the most common specifications for hydraulic fluids, engine oils, greases, and other aviation lubricants, how qualification works, and how to identify the correct lubricant for your aircraft.