Purpose of engine oil

In operation, engine oil is exposed to a wide variety of influences. Therefore, it is very difficult to accurately determine the effect of various operating influences on an engine lubricant. Engines that run at high speeds or at full load for long periods of time reach high temperatures. Under the influence of high temperature and atmospheric oxygen, the process of oil oxidation begins. Oxidation products thicken the oil and can form varnish-like deposits on the upper parts of the pistons, in the grooves for the piston rings and on the valve stems. This can lead to sticking of the valve heads.