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Aircraft Oil: Mineral Vs. Ashless Dispersant And The Problem With Synthetic

Shell Oil

There's a lot of discussion about what oil is best to use for your aircraft engine. We did some research, and here's what we found.

Oil Types - Mineral, Ashless Dispersant, And Synthetic

There are two main oil types used in aircraft engines: mineral oil and ashless dispersant (AD) oil. Both types are made of mineral oil - a refined, petroleum based oil. However, AD oils have added chemicals (additives), which collect debris inside the engine and carry them to the oil filter.

Unlike mineral and AD oil, synthetic oil is not made from whole crude oil. There are some synthetic blend oils used in aircraft engines, but they aren't as common. Shell Oil tested all-synthetic oils in aircraft engines, and what they found wasn't good. At 600 to 900 hours, the engines began to burn more oil and lost compression. "When the engines were disassembled, we found that the piston rings were covered with a gray tacky substance that was primarily made up of the lead by-products of combustion." Read the report here.

What Oil Type Should Be Used For Break-In

Many pilots have learned to use straight mineral oil while breaking in a new engine. It's thought that mineral oil is less viscous (less slippery) than AD oil, and that it will allow the piston rings to wear in the cylinder walls more quickly. However, not all manufacturers recommend this practice. The Continental Motors engine break-in guide recommends straight mineral oil, while Lycoming recommends AD oil when breaking in all turbocharged engines. What should you use? Check your engine's manual and follow the manufacturer's instructions - always the best bet for long engine life.

Colin Cutler

Colin is a Boldmethod co-founder, pilot and graphic artist. He's been a flight instructor at the University of North Dakota, an airline pilot on the CRJ-200, and has directed development of numerous commercial and military training systems. You can reach him at colin@boldmethod.com.

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