Degradation of the oil also occurs due to its contamination with other substances. Engine oil can be contaminated with fuel, water or coolant, particles or impurities.
Contamination with fuels (gasoline or diesel) has the effect of lowering the viscosity which involves poor lubrication of moving parts. It also lowers the flammability temperature of the oil, which can cause it to ignite.
Contamination with water or coolant leads to emulsification of the oil and reduced lubrication capacity. Also, the viscosity of the oil increases and the additives can be separated from the oil, which leads to a drastic reduction in the lubricating capacity of the oil.
Particulate contamination is due to incomplete combustion of the fuel and leads to an increase in the viscosity of the oil. The oil can also be contaminated with metal particles (from parts) or impurities in the air. Oil particles, if they come in contact with metal surfaces, lead to intensification of the wear process.
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