Viscosity is one of the important indicators for selecting lubricating oil, and lubricating oil should be selected according to the speed, load, temperature, power, size, etc. of the friction parts of the equipment. If the viscosity of lubricating oil is too low, it will form semi liquid lubrication or boundary lubrication, which will accelerate the wear of the moving pair and also be prone to oil leakage; If the viscosity is too high, it will result in poor fluidity, poor heat dissipation, high internal friction resistance, high power consumption, and also increase the wear of the motion pair.

• Common testing instruments: automatic viscosity tester
  
• Execution standards: GB/T265, ASTM D445, etc
  

Moisture can promote emulsification of oil products, reduce viscosity and oil film strength, promote oxidation and deterioration of oil products, increase oil sludge, aggravate the corrosion of components by acidic oil products, and cause the precipitation of additives in oil products, rendering them ineffective.

• Common testing instruments: moisture analyzer
  
• Execution standards: GB/T 260, ASTM D95, etc
  

Acid value is one of the indicators to ensure that the components are not corroded. During the use of oil, the acid value continuously increases due to oxidation and decomposition. When it reaches a certain level, new oil should be replaced to avoid corrosion of the components. It is worth noting that when changing the oil, the old oil should be cleaned thoroughly, otherwise it will accelerate the oxidation of the new oil and shorten its service life.

• Common testing instruments: fully automatic acid value analyzer
  
• Execution standards: GB/T 7304, ASTM D664, etc
  

Mainly refers to precipitates or suspensions that are insoluble in solvents such as gasoline, ethanol, or benzene in lubricating oil, and are derived from external pollution or mechanical wear during the production, storage, and use of lubricating oil. Particulate pollutants are one of the important indicators for measuring the quality of lubricating oil. Their presence can damage the oil film, accelerate the wear of motion pairs, and even wear down parts, block oil circuits or filters, causing equipment lubrication failures and affecting normal production.

• Common testing instruments: particle counter (shading method)
  
• Execution standards: NAS 1638, ISO 4406, GJB420, etc
  

The highest temperature at which the lubricating oil sample stops flowing under specified conditions is called the pour point, while the lowest temperature at which the cooled sample can flow under specified test conditions is called the pour point. The pour point or freezing point of lubricating oil is an important indicator of its low-temperature fluidity. Oil with a pour point lower than the lowest external temperature should be selected as lubricants in low-temperature environments.

• Common testing instruments: pour point analyzer
• Execution standard: GB/T 510-83 (condensation point)
                                   GB/T 3535-83 (pour point)
  

The flash point of lubricating oil is the lowest temperature at which the volatile oil and gas on the surface of the oil ignite under specified test conditions. When the volatile oil and gas on the surface of the oil mix with oxygen in the air, if the flash point is low, it is more likely to flash. Open flash point is commonly used to determine lubricating oil, while closed flash point is commonly used to determine kerosene, diesel, transformer oil, etc.

• Common testing instruments: Open flash point tester
  
• Execution standard: GB/T 267-88 (open flash point)