Any liquid has a viscosity, it is this characteristic that determines its fluidity. Automotive oil is designed to perform a number of tasks, so each parameter has its own effect on quality in general. Oil viscosity is no exception.
The main technical task of any engine oil is to stop the friction of moving parts during engine operation. Ideally, the friction force should be minimal with high durability of the oil, its properties should remain constant over a wide temperature range.
Putting this idea into practice and creating a substance that meets all the requirements is very difficult. In addition, it must be borne in mind that during movement, the load is constantly changing, and the temperature of automobile oil in the engine will be very different, at some points it will reach 140-150 degrees.
Nevertheless, experts are constantly working on the creation of motor oil, which would be as close as possible in its properties to the necessary parameters. Science has made a rather large step forward in this direction, so modern engines are much more powerful and efficient than their predecessors, and they work longer.
Oil viscosity is one of the most important parameters. While the engine is cold or does not work at full strength, the oil in the engine begins to gradually thicken. In this regard, there is a requirement that the oil must remain liquid under any circumstances, even if the outdoor temperature is much lower than zero. The better the fluidity of the oil, the better it will protect the engine during operation.
Oil Viscosity Index
To determine the viscosity of the oil, experts have introduced a special index that reflects the dependence of changes in the main parameters (including viscosity) on temperature. The higher the index, the better the oil retains its fluidity even at low temperatures.
The oil must, under any circumstances, remain on the engine parts, but at the same time maintain its fluidity. Oil classification, as a rule, is made according to the index, as this is one of the most important indicators, which to one degree or another reflects the main characteristics.
The 5W index indicates that the engine can be started even at a temperature of - 35 degrees without preliminary heating. The lower the temperature, the thicker the oil will become, and this already complicates the “cranking” of the engine, which means that the starter can no longer crank the engine. When choosing a specific automobile oil, you always need to focus on the main tasks, but without forgetting the recommendations of the car manufacturer. It is necessary to take into account the design of the engine, the degree of wear, the most frequent modes of operation, etc.
Engine performance
Among other things, the viscosity of the oil affects the efficiency of the engine, namely the distribution of energy. When the engine is running, some of the energy is consumed for internal needs, i.e. this means that the engine needs energy to overcome the frictional force that occurs when various parts come into contact. The better and more effective the oil, the less energy will be spent on it.
The oil classification introduced by the American Society of Automotive Engineers is currently in use. To get this or that category, the oil must meet some requirements. The kinematic viscosity of the oil is determined at temperatures of 40 and 100 degrees, and is measured when passing through a special curved tube - a viscometer. Based on this, the real viscosity of the oil is determined, for the detection of which a special formula is used. Such tests allows you to determine the quality of the oil, as well as assign a certain category.