. The gasoline engine should choose SD-SF grade gasoline engine oil according to the additional equipment and use conditions of the intake and exhaust system, and the diesel engine should choose CB-CD grade diesel engine oil according to the mechanical load, which is not less than the requirements of the manufacturer. Any quality grade of the lubricating oil in the process of use of oil will change, to a certain mileage, the deterioration of the performance of the lubricating oil, will bring various problems to the engine. In order to avoid failures, regular oil change should be combined with the conditions of use, and make the oil quantity moderate (generally the upper limit of the oil gauge is good). When the oil passes through the pores of the filter, the solid particles and viscous substances in the oil will accumulate in the filter. If the filter is blocked, the oil can not pass through the filter core, it will dilate the filter core or open the safety valve, through the bypass valve, it still brings the dirt back to the lubricating part, so that the machine parts are worn and the internal pollution is aggravated. Now most of the gasoline engines are equipped with PCV valves (crankcase forced ventilation) to make the engine ventilated, but the pollutants in the gas channeling will be deposited around the PCV valve, which may cause the valve to be blocked. If the PCV valve is blocked, the polluted gas converse into the air filter, pollutes the filter core, reduces the filtration capacity, and the inhaled mixture is dirty, causing the pollution of the crankcase, which leads to the increase of fuel consumption, the increase of the engine wear and even the damage to the engine. Therefore, regular maintenance of PCV should be carried out to remove pollutants around the PCV valve.