Used oil, also called lubrication oil, is a variety of machinery, vehicles, ships to replace the lubricating oil, in the process of use by external pollution to produce a large number of gum, oxide and thus lose efficacy. The main reasons: First, the oil in use is mixed with moisture, dust, other miscellaneous oil and metal powder produced by mechanical wear, resulting in black color and greater viscosity. Second, the oil deteriorates over time, forming organic acids, colloid and asphalt-like substances.