The structure of diesel filters is roughly the same as that of oil filters, with two types available: replaceable and spin on. But its working pressure and oil temperature resistance requirements are much lower than those of oil filters, while its filtration efficiency requirements are much higher than those of oil filters. The filter element of diesel filters mostly uses filter paper, and some also use felt or polymer materials. Diesel filters can also be divided into diesel water separators and diesel fine filters. The important function of the oil-water separator is to separate water from diesel fuel. The presence of water poses great harm to the fuel supply system of diesel engines, as rust, wear, seizure, and even deterioration of the combustion process of diesel. Due to the high sulfur content in Chinese diesel, during combustion, it may even react with water to form sulfuric acid that corrodes engine components. The traditional water removal method mainly involves sedimentation, which is achieved through a funnel structure. Engines with emissions above the third grade require higher requirements for water separation, which requires the use of high-performance filtration media.

There is only one possibility of water ingress into the diesel filter element, and it is impossible for water to be generated in the fuel tank out of thin air due to external entry. So either it's the quality of the diesel, or there's water entering the fuel tank somewhere. If there is a lot of water in the diesel filter element, focus on checking whether the fuel tank cap is sealed and whether there are leaks in the upper part of the fuel tank.

Solution:
1. Turn off the fuel tank switch, remove the oil pipe, and then open it again. Make the water flow inside the container, turn off the switch when the diesel flows out, and install the oil pipe. Sediment the effluent from the container, and after separating the oil and water, pour the upper layer of diesel back into the fuel tank.
2. Remove the plug below the filter to allow diesel fuel to flow into the container. Tighten the plug after the diesel oil flows out. Dispose of the effluent inside the container according to the above method.