The evaporation loss of oil refers to the amount of oil lost through evaporation under certain conditions, measured by massExpressed as a percentage. The evaporation loss is directly proportional to the volatility of the oil product. The greater the evaporation loss, the higher the fuel consumption in practical applications, so there should be limitations on the amount of evaporation loss of oil products under certain conditions. Lubricating oil evaporates during use, causing a gradual decrease in the amount of lubricating oil in the lubrication system that needs to be replenished, increasing viscosity and affecting oil supply. Hydraulic fluid evaporates during use, leading to cavitation and decreased efficiency, which may cause damage to the hydraulic pump. The data obtained by distillation method is only a rough result, and the evaporation loss of lubricating oil products needs to be determined by specialized methods. At present, the method for determining the evaporation loss of lubricating oil in China is GB/T 7325 Determination of Evaporation Loss of Lubricating Oil and Lubricating Grease. This method involves placing the lubricating oil sample placed in the evaporator in a constant temperature bath at a specified temperature, allowing hot air to pass through the surface of the sample for 22 hours. Then, the evaporation loss is calculated based on the mass loss of the sample. According to this method, the evaporation loss of lubricating oil can be measured at any temperature within 99-150 ℃. At present, this method is mainly used for evaluating the evaporation loss of synthetic lubricants in China. The main measurement methods abroad include ASTM D972 from the United States, DIN 51581 from Germany, and JIS K2220 (5.6) from Japan.