The main indicators of lubricating oil are:

　　Viscosity, viscosity index, pour point and freezing point, flash point and fire point, ash content, carbon residue value.

　　1、Viscosity is the speed at which lubricating oil flows at a certain temperature, and it changes with temperature. Generally, the viscosity at 40°C and 100°C is used as the standard for high temperature grease manufacturers. Viscosity is an index for the classification and grading of various lubricating oils, which is decisive for quality identification and determination.

　　2、Viscosity index is a conventional quantity that expresses the characteristic of oil as a function of temperature. The higher the viscosity index, the more correct the viscosity of the oil with temperature changes.

　　3、Pour point and freezing point Pour point is the lowest temperature at which the cooled sample can flow under specified conditions, and freezing point is the maximum temperature at which the sample is cooled to stop moving under specified conditions, both expressed in °C. The pour point or pour point is a conditional test value and does not equal the actual flow limit in use.

　　4、Flash point The flash point of lubricating oil is a safety index for the storage, transportation and use of lubricating oil, and it is also the volatility index of lubricating oil. Lubricating oil with low flash point has high volatility, easy to catch fire, poor safety, high volatility of lubricating oil, easy evaporation loss during the working process, and even increase the viscosity of lubricating oil in severe cases, affecting the use of lubricating oil. If the flash point of heavy lubricating oil suddenly decreases, a light oil mixing accident may occur. From a safety point of view, the safety of petroleum products is classified according to their flash points: those with a flash point below 45°C are flammable low-temperature oils, and those with a flash point above 45°C are flammable.

　　5、The ignition point, also known as the ignition point, refers to the temperature at which the mixture of steam and air on the surface of the flammable liquid contacts the fire and the flame can continue to burn for no less than 5s. It is possible to continue the determination in the same standard instrument after the determination of the flash point. The flash point and ignition point of flammable liquids indicate the possibility of explosion or fire, and have a great relationship with the safety of transportation, storage and use.

　　6、The ash content of lubricating oil is the residue (non-combustible) left after the lubricating oil is completely burned under specified conditions. The ash content of lubricating oil is mainly composed of metal salts and metal oxides generated after the complete combustion of lubricating oil. Lubricating oils with additives have higher ash content. The existence of ash in the lubricating oil increases the carbon deposition of the lubricating oil during use. When the ash content of the lubricating oil is too high, it will cause the wear of mechanical parts.

 　7、Carbon Residue Value In lubricating oil, asphaltenes, colloids and polycyclic aromatic hydrocarbons are the main substances that form carbon residues. Therefore, carbon residue is an indirect indicator of colloidal substances and unstable compounds in oil products. The larger the carbon residue, the more unstable hydrocarbons and colloidal substances in the oil, and vice versa. According to the size of the residual carbon, the tendency of oil to form carbon in the compressor can be roughly determined. For lubricating oil, the residual carbon dry lubricant value can indirectly indicate the refining degree of the lubricating oil. The more refined the lubricating oil, the smaller the residual carbon value.