It is useless to change the oil without changing the filter: 
1. The oil filter is the oil filter, which is located in the engine lubrication system. The upstream is the oil pump, and the downstream is the parts of the engine that need to be lubricated. The role of machine filtration The oil itself contains a certain amount of colloids, impurities, moisture and additives. At the same time, during the operation of the engine, the introduction of metal wear debris, the entry of impurities in the air, and the production of oil oxides gradually increase the amount of debris in the engine oil;
2. The oil filter filters out harmful impurities in the oil from the oil pan, and supplies clean oil to the crankshaft, connecting rod, camshaft, piston ring and other moving parts to play the role of lubrication, cooling and cleaning, and extend the life of the parts. The machine filter should be replaced regularly. After a long period of use, the filter performance will decrease, and the pressure of the oil passing through the filter will be greatly reduced;
3. When the oil pressure drops to a certain level, the filter bypass valve will open, and the unfiltered oil will enter the oil circuit through the bypass. Impurities will increase the wear of the machine parts. In severe cases, it will even block the oil passage and cause mechanical failure. Therefore, the machine filter should be replaced regularly;
4. For cars that are frequently used in the engine filter replacement cycle, the oil filter should be replaced every 7500km. Under severe conditions, such as frequent driving on dusty roads, it should be replaced every 5000km. Therefore, when changing the oil, you must change the filter instead of replacing the filter, so about 25% of the pollutants in the old filter will re-enter the oil circulation, which not only increases the chance of wear, but also reduces the performance of the new oil;
5. Therefore, the filter must be changed when changing the oil, which is beneficial to prolong the service life of the engine.