Types of Engine Oil

Types of oils are derived from specifications developed by the military in the 1940s and later standardized by the Society of Automotive Engineers (SAE). For the written test, be mindful of the following technical terms, characteristics, and types of lubricating oils used in the aviation piston engine industry.

Viscosity

Viscosity is the measure of the oil’s resistance to shear or flow. High viscosity indicates a high resistance to flow (e.g. maple syrup) while low viscosity indicates a low resistance (e.g. water). It varies with temperature and pressure. Increasing temperature causes viscosity to decrease, conversely reducing temperature causes viscosity to increase.

Consider the use of oils with high viscosity in warm environments and oils with low viscosity in colder environments but always refer to the AFM/POH for details regarding the use of approved oils.

Ashless Dispersant

Ashless dispersants are additives designed to minimize deposit formation. They do not contain metal compounds, which would contribute to deposits in the combustion chamber. The dispersants help prevent contaminants from forming sludge that could plug oil passageways. They help the oil suspend combustion by-products, keeping them dispersed until the oil is drained.

Mineral Oil

Mineral oil is usually used during an engine break-in, however, always consult with the AFM/POH for engine break-in procedures.