Lubricating oils are essential to ensure the proper functioning of an engine. They are composed of base oils of petroleum or synthetic origin and additives. The latter confer good properties to lubricating oils. However, these characteristics can be lost after use. The lubricating oils of the engine type become black during its use, and this is due to their degradation because of several phenomena, such as oxidation, contamination, as well as corrosion and other phenomena. The results obtained showed well, that this engine oil degrades quickly, and also remarkable with the change of color that becomes more and more black, contains solid contaminants that can be the cause of engine damage. In addition, of the mills in the Dibindi market, 94% are equipped with single-cylinder diesel engines. Of these 94%, only 29% of the mills reuse the used oil, and 48% of the users do so because of lack of financial means, and 43% prefer to earn a lot of money by reducing the expenses related to the purchase of new oil. 49% do not know the negative consequences that would happen if they reuse used oil; and finally, in the single-cylinder diesel engines targeted, 25% of the breakdowns are due to bad lubrication or bad lubricants.