Disadvantage 2: the filtration efficiency is zero under special conditions;
　　There are bypass valves at the bottom of the paper filter element, which is a direct oil flow channel designed in order to ensure the smooth circulation of oil back to the engine when the engine starts cold and the oil viscosity is high or the paper filter element is partially or completely blocked. When the engine oil opens the bypass valve under the pressure of the oil pump, the engine oil circulating back to the engine through the bypass valve not only cannot get the filter of the paper filter core, but also will have been the original filter out of the paper filter core of the large particles of impurities, through the bypass valve back to the engine, to the engine brings uninterrupted secondary wear. From the above two shortcomings, it can be seen that impurities larger than or smaller than the paper filter core microholes do not have a permanent filtering effect on impurities, only those equal to the paper filter core microholes and embedded into the paper filter core microholes have a permanent filtering effect on impurities, so the filtering efficiency is very low.