Illegal operation and improper use. The vehicle diesel engine has large heat load and pressure and harsh working conditions. It should be operated according to the regulations, especially during the running in and adjustment period of the new diesel engine. It should be operated according to the regulations and must not be used against regulations. However, new car owners are often eager for quick success and instant benefit. Therefore, high-speed full load operation or overload high-speed operation for a long time; After cold start or before flameout, slam the accelerator, increase the accelerator at low gear on steep slopes in mountainous areas, and drive as usual when the oil pressure is too low and the alarm light is on; If the water temperature and oil temperature are too high, instead of cooling in time, it will stall and slide at high speed, resulting in sudden reduction of oil pressure and other bad driving behaviors, which will lead to poor lubrication and even greater faults.

2)机油品质差，黏度级不当。按照通用的API(美国石油学会)质量标准，机油分CA、CB、CC、CD4个等级，按照通用的SAE(美国汽车工程师协会)标准，机油黏度分为6个等级，不同牌号相同品质的黏度等级的机油可互换使用，但不可混合使用。因此，在更换或添加机油时应严格遵守上述原则，且按照柴油机制造公司提供的使用说明书选用规定的机油。违规混合添加不同品质和黏度的机油，甚至使用劣质机油或不按规定周期更换机油等行为，都将导致润滑条件恶化。

2) Poor oil quality and improper viscosity grade. According to the international general API (American Petroleum Institute) quality standard, the engine oil is divided into four grades: Ca, CB, CC and CD. According to the international general SAE (American Society of Automotive Engineers) standard, the engine oil viscosity is divided into six grades. Engine oils of different brands and the same quality can be used interchangeably, but not mixed. Therefore, the above principles shall be strictly observed when replacing or adding engine oil, and the specified engine oil shall be selected according to the operation manual provided by the diesel engine manufacturer. Illegal mixing and adding engine oil of different quality and viscosity, even using inferior engine oil or changing engine oil not according to the specified cycle will lead to the deterioration of lubrication conditions.

3)冷却散热不良，油温过高。机油冷却器在润滑系统中工作环境较差，散热管易积附油垢，使冷却散热效果下降，若检修不及时，机油温度过高，黏度下降，将导致机油蒸发。一方面机油蒸气与燃烧不完全的水蒸气、空气及透过空滤进入柴油机的灰尘混合，改变机油的性质，影响机油的流量，破坏正常的润滑;另一方面机油蒸气使散热管接头焊缝薄弱部位渗漏，使出油口周围密封件性能降低，密封较差部位泄漏，导致机油消耗增加，机油劣化速度加快。在柴油机润滑系统中，应注意对机油冷却器的检验和维护。

3) Poor cooling and heat dissipation, high oil temperature. The working environment of the oil cooler in the lubrication system is poor, and the heat dissipation pipe is easy to accumulate oil dirt, which reduces the cooling and heat dissipation effect. If the maintenance is not timely, the oil temperature is too high and the viscosity decreases, which will lead to the evaporation of the oil. On the one hand, engine oil vapor is mixed with incomplete combustion steam, air and dust entering the diesel engine through the air filter, which changes the nature of engine oil, affects the flow of engine oil and destroys normal lubrication; On the other hand, the oil vapor makes the weak parts of the joint weld of the heat dissipation pipe leak, which reduces the performance of the seal around the oil outlet and leaks at the parts with poor sealing, resulting in increased oil consumption and accelerated oil deterioration. In the lubrication system of diesel engine, attention should be paid to the inspection and maintenance of oil cooler.

4)维修不善。日常不注意维护，不按规定维护，柴油机损坏后才修理，甚至发现小故障也不及时修理凑合使用，使机油集滤器堵塞，机油泵磨损，润滑系统管路破裂，油底壳中机油存量不足，油压感应塞或线路损坏，以及机油滤清器滤芯太脏，或旁通阀开启等，均会导致供油不足，油压过低。此外检修技能或选配品质不高，装配不清洁，装配零件时扭紧力矩过大，使运动部件间夹入杂质，以及配合间隙过小等，均会降低机油流量形成局部干摩擦。

4) Poor maintenance. Do not pay attention to daily maintenance, do not maintain according to regulations, repair the diesel engine only after it is damaged, and even do not repair it in time in case of minor faults, so as to make do with it, resulting in blockage of oil filter, wear of oil pump, rupture of lubrication system pipeline, insufficient oil stock in oil pan, damage of oil pressure sensing plug or pipeline, dirty oil filter element, or opening of bypass valve, etc, Will result in insufficient oil supply and low oil pressure. In addition, poor maintenance skills or matching quality, unclean assembly, excessive tightening torque when assembling parts, inclusion of impurities between moving parts, and too small matching clearance will reduce oil flow and form local dry friction.