For instance, an aircraft piston engine generally requires a fairly heavy oil to provide good lubrication due to design, cooling, and normal engine operating parameters. Other times, it can be difficult to identify a single oil that will function adequately in the entire range of operating or environmental conditions that an engine may be subject to. Sometimes, all of these criteria can result in a scenario where almost any oil will do, although it may not be optimal. Generally, we use the lowest viscosity oil in an application that will support the required loads. The ideal oil for a given application will be viscous enough to ensure a proper fluid film under all operating conditions, yet fluid enough to avoid power losses resulting from excessive fluid friction. That is heavily influenced by the speed, load, and surface temperatures that the surfaces will be exposed to in operation. Basically, the oil must be thick enough to provide an adequate separation of the lubricated surfaces. When application speeds are reduced or operating temperatures are increased, the viscosity of the oil required to provide lubrication also increases.Ĭhoosing an oil with the correct viscosity for any given application requires consideration of all the operating and environmental factors that the lubricated surfaces will be subject to in use. Generally, low viscosity oils are preferred for applications where either high speeds or low temperatures and pressures are present. Viscosity characteristics of the oil will also affect things like oil consumption rates, low-temperature oil flow to the engine, and the speed at which the engine will crank - especially if the ambient temperatures are cold.įactors such as application speed, load, and operating temperature are all important factors influencing the choice of the correct oil to apply in any application. A properly formulated engine oil of the proper viscosity grade will provide a lubricant film in-between moving parts in the engine and protect them from wear. It’s important to understand that the viscosity of engine oil changes continuously as the temperature of the oil changes. By definition, viscosity is a measure of oil’s resistance to flow, and it is measured at one or more standardized temperatures so that we can define viscosity grades of engine oils. Viscosity is probably the single most important characteristic of oil that affects the engine.

Define viscosity of oil