Reliable and long-term operation of modern diesel engines largely depends on the quality of the engine oils used. In this case, the oil in the diesel engine is exposed to high temperatures and pressures, comes into contact with metals, and is also in contact with exhaust gases and oxygen in the air. As a result, various kinds of deposits form on the parts of the diesel engine. Depending on the nature of the deposits, they are conditionally divided into high-temperature (varnishes, deposits) and low-temperature (precipitation). Increased formation of low-temperature deposits in the channels of the lubrication system, valve cover, crankcase, on the details of the valve timing mechanism, filter elements, oil intake grid leads to a decrease in the amount of oil supplied to the most critical friction units lubricated under pressure, and overheating of the engine. In general, the increased tendency of motor oils to form low-temperature deposits significantly reduces the service life. Currently, in the Russian Federation, motor methods for assessing the propensity of motor oils to form low-temperature deposits for diesel engines have been lost. The FAA "25 State Institute of Chemical Biology of the Ministry of Defense of the Russian Federation" has developed a new motor method for assessing the propensity of motor oils to form low-temperature deposits on diesel engine parts. It is shown that the developed motor method is sensitive to changes in the component composition of engine oil, the tendency to form low-temperature deposits decreases with the involvement of base oils of group III and IV, as well as with a decrease in the mass fraction of the low-viscosity component in the base oil.