As we've discovered, an airplane's engine cannot run without fuel. Another valuable fluid that is required for the engine to run is oil. We've already discussed how the oil cools the engine, but other equally important functions of oil is to lubricate the moving parts of the engine, Provide a protective coating to prevent corrosion and remove dirt and other particles from the engine.

There are two types of oil systems, a wet sump system and a dry sump system. A wet sump system, like that of a Cessna 172, is a system in which the oil is located in a tank at the base of the engine. This makes it an integral part of the engine. On the other hand, a dry sump system has a separate oil tank, which separates the oil system from the engine.

Let's take a journey through the oil system of a typical general aviation airplane. As oil leaves the sump, it is routed through a strainer screen as to not allow any solid contaminants to flow through the system and damage it. After leaving the strainer, it passes through the pump. Leaving the pump, the oil is then routed into either the oil cooler, if it is hot and needs to be cooled, Or it bypasses the cooler if it's already cool enough.

Next, the oil proceeds to the oil filter, which removes any contaminants that made it through the strainer. Finally, the oil is sent to the engine for lubrication, cooling, and cleaning. When the oil has finished its journey, gravity pulls it back to the sump. Since oil is so important for the engine, it's imperative to check the oil level prior to flying.

The minimum and maximum amounts are specified in the airplane's flight manual. While flying, it's also important to regularly check oil pressure and oil temperature. Anything outside of the normal range, which is usually designated by a green arc, may potentially lead to major problems, including engine failure.

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