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)機油品質差，黏度級不當。按照通用的API(美國石油學會)質量標準，機油分CA、CB、CC、CD4個等級，按照通用的SAE(美國汽車工程師協會)標準，機油黏度分為6個等級，不同牌號相同品質的黏度等級的機油可互換使用，但不可混合使用。因此，在更換或添加機油時應嚴格遵守上述原則，且按照柴油機制造公司提供的使用說明書選用規定的機油。違規混合添加不同品質和黏度的機油，甚至使用劣質機油或不按規定周期更換機油等行為，都將導致潤滑條件惡化。

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)冷卻散熱不良，油溫過高。機油冷卻器在潤滑系統中工作環境較差，散熱管易積附油垢，使冷卻散熱效果下降，若檢修不及時，機油溫度過高，黏度下降，將導致機油蒸發。一方面機油蒸氣與燃燒不完全的水蒸氣、空氣及透過空濾進入柴油機的灰塵混合，改變機油的性質，影響機油的流量，破壞正常的潤滑;另一方面機油蒸氣使散熱管接頭焊縫薄弱部位滲漏，使出油口周圍密封件性能降低，密封較差部位泄漏，導致機油消耗增加，機油劣化速度加快。在柴油機潤滑系統中，應注意對機油冷卻器的檢驗和維護。

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)維修不善。日常不注意維護，不按規定維護，柴油機損壞后才修理，甚至發現小故障也不及時修理湊合使用，使機油集濾器堵塞，機油泵磨損，潤滑系統管路破裂，油底殼中機油存量不足，油壓感應塞或線路損壞，以及機油濾清器濾芯太臟，或旁通閥開啟等，均會導致供油不足，油壓過低。此外檢修技能或選配品質不高，裝配不清潔，裝配零件時扭緊力矩過大，使運動部件間夾入雜質，以及配合間隙過小等，均會降低機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.