<p>This article is devoted to the development of threshold values for motor oil quality indicators under the climatic conditions of the Republic of Uzbekistan. The quality of engine oil significantly affects not only the main operational <br /> performance, service life, and technical condition of the engine, but also oil consumption and oil change intervals. The oil change interval depends on its threshold values under operating conditions. Although general recommendations are provided by manufacturers, in practice oil change intervals vary significantly depending on a wide range of factors such as climate, road conditions, load level, fuel quality, and driving style. Therefore, determining the optimal oil change <br /> interval under local operating conditions is an important scientific problem in the field of vehicle maintenance. Under different operating conditions, various changes occur in the engine oil properties of vehicles. The article studies the combined influence of key oil quality indicators, such as kinematic viscosity, alkalinity, flash point, and density. Based on the analysis results, patterns of change in oil quality indicators depending on vehicle mileage were established. The results show that under local operating conditions, the degradation of engine oil begins to appear after 8000 km. It was scientifically proven that the optimal oil change interval for diesel engine trucks operating in the climatic conditions of Uzbekistan is 8000±1000 km. </p>