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Why must engine lubricants have good cleaning and dispersing properties? Unburned fuel, organic acids, smoke, moisture, sulfur oxides, and nitrogen oxides from the gases that leak out of the combustion chamber end up in the crankcase, mixing with the lubricant. When the engine is operated at high temperatures, the oil itself produces various oxidation products. These products, along with metal particles resulting from wear of the components, mix together to form sludge deposits within the oil. This type of sediment, in small quantities, remains suspended in the oil; but when its amount increases, it precipitates out of the oil. It has the following effects on the engine: clogging of filters and oil passages, poor flow properties of the oil, difficulties in supplying oil, coking in the piston ring grooves, sticking of the piston rings, increased fuel consumption, and reduced power output. To prevent the aforementioned failures, it is necessary to remove sludge from the engine lubricant or to convert it into a harmless suspension within the oil; this is achieved by adding soluble detergent and dispersant additives to the oil. Furthermore, in gasoline engines, the main problem is the formation of low-temperature sludge due to moisture in the oil, which can cause severe blockages in the oil circulation system; therefore, ash-free detergents and dispersants should be used more frequently.