Additives are chemical products blended into base oils with the intention of:
• Improving the lubrication properties of oil over all operating conditions.
• Reinforcing and enhancing positive qualities of the base oil.
• Reducing or eradicating undesirable oil properties.
The overall purpose of oil additives is to modify the properties of lubricating oils so they protect vehicle engines under all operating conditions while reducing emissions and enhancing engine oil life. The percentage of additives in oil can vary from a few per cent to as high as 25per cent. Additive packages are carefully designed to ensure motor oils comply with the relevant API or ACEA specification and is suitable for use in all engines requiring oil to those specifications.
Chemicals used as additives include molybdenum compounds and fatty acids to reduce friction, phosphates and polysulphides as anti-wear agents, and antioxidants to prevent oil oxidation that results in deposits and thickening of the oil. Rust and corrosion inhibitors are used to prevent attack by organic acids present in oil and from acids produced as a result of combustion. Detergents, or soaps, made from metallic compounds of sodium, potassium, and calcium neutralize acids, and dispersants keep products of combustion and other contaminants in suspension, keeping engines clean.
Other additives improve the viscosity profile of oil so that as oil heats up, viscosity changes are minimized, ensuring good start-up lubrication as well as retaining sufficient viscosity to effectively lubricate engines when they are hot. These additives are long chain polymers and known as viscosity index improvers. A particular problem experienced in cold winter weather is that waxes in the oil crystallize and make it difficult or even impossible to pump engine oil, leading to engine failure. Pour point depressants are used to reduce the temperature at which waxes crystallize.