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Caring For Your Aircraft

Part IV: From selecting the correct grade to changing it at correct intervals, knowing your oil is important

Oil is to an aviation piston engine what blood is to the human body: a crucial element in keeping it alive. Though blood fulfills the task by carrying nutrients to the various cells in the body, oil accomplishes the same function by creating a microscopic film between metal parts that keeps them from grinding each other into oblivion from heat and friction. Oil also carries the nasty by-products of combustion away from the critical parts of the engine, and holds them in suspension until your next oil change. Oil also disperses the intense heat created during combustion. In all, oil is your engine's best friend.

There's much hearsay about engine oil and oil changes in the piston aviation world. It seems everybody has an opinion and advice, though much of it isn't based on fact or comes from old ideas. The oil we use in our airplanes today isn't your grandfather's oil (though many of us miss oil cans), and understanding modern techniques and formulations will help us squeeze more life out of our engines. In the end, isn't that what it's all about?

We were fortunate to talk with Paul Royko, AeroShell's Technical Manager of piston-engine oil, who speaks frequently at aviation events and conferences. Though he won't admit to it, Royko is something of an aviation-oil guru, and his advice is something all pilots can benefit from. AeroShell has been providing oil to aviators since they developed the first ashless dispersant aviation oil in the early 1950s. In the 1960s, Aeroshell made headlines again when they developed their now-famous Turbine Oil 555, which was created especially for the Concorde, and could withstand the high-bearing temperatures and stresses of supersonic flight.

"The best advice I can give to pilots is simple," says Royko, "Pick the proper oil for the conditions you fly in. The other critical thing is to change the oil and filter at the proper intervals, and finally, fly often. Those three simple things will extend the life of your engine and your oil, and will help you catch problems early."

How Oil Works

To put that advice into practice, it helps to understand the seemingly simple process of how the oil works in your engine. In a cold engine, the oil sits in the oil sump, pulled by gravity to the lowest point in the system. When you start the engine, oil is pulled out of the sump by an engine-driven oil pump. It's sent through the oil filter (or oil screen if you don't have a filter), and proceeds into the crankcase, where it lubricates the critical bearings and other components. Oil travels into the cylinders, where it creates a seal between the piston rings and the smooth walls of the cylinders, allowing compression to occur.

The oil carries away heat through convection as it travels through the engine. Typically, the oil will travel through an oil cooler, where air flow will carry the transferred heat away. Microscopic bits of metal that are the result of friction also will be carried away, and will end up in the oil filter.

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