（1）Improper selection of lubricating oil : different parts of the reducer have different requirements for the variety, viscosity and other properties of the lubricating oil. Proper lubricating oil can reduce the conflict resistance between the internal contact surfaces, and also reduce the wear of the gear surface and the noise and vibration of the transmission. Improper selection makes the smoothing effect greatly weaken, the gears and other surfaces will contact each other, and pressure will concentrate, which will seriously damage the gear surface and even damage the equipment.
（2）Too much lubricating oil : During the high-speed operation of the reducer, the oil pool is vigorously stirred, and the lubricating oil bursts into the reducer. If lubricating oil is too much, it will accumulate in the shaft seal, end cover, joint surface, etc., resulting in oil leakage, which will increase the running resistance of rotating parts such as bearings and gears, increase power consumption, and reduce heat dissipation space. High oil temperature and decreased viscosity make the oil film thinner, destroying the normal smooth condition of the conflicting surface, and making the equipment wear severely.
However if the lubricating oil is less, the gears, bearings and joint surfaces of the reducer will not get enough to form oil film, resulting in dry conflict, which also causes severe equipment wear.
（3）Air, mechanical impurities, free water and other pollutants in the lubricating oil : When the reducer is in operation, the lubricating oil in the machine is easily affected by mechanical impurities, water, air and other pollutants. For example, free water can make the lubricating oil acid substances corrode metal parts and increase wear. The air mixed in the oil can cause the oil to oxidize and deteriorate, and even cause the metal parts to oxidize and corrode. The impurities reduce the cleanliness of the oil, deteriorate the oil quality, and reduce the viscosity level, which result in jamming, failure of the speed control system, and even equipment damage.