The Role of Additives in Motor Oil Performance

Most lubricating oils are formulated with chemical additives that enhance the beneficial properties of the base oil or make up for oil deficiencies. For passenger car motor oils, base oil makes up 70 to 80 percent of the final product; additives comprise the other 20 to 30 percent.

Additives

help lubricants withstand extreme operating environments. Even the best base oil cannot protect as well against the effects of heat, shearing forces, chemical and water dilution, corrosion and wear particles. In short, additives enhance lubricant funtioning by performing two critical functions:

• Additives lessen destructive processes
• Additives enhance beneficial properties of the base oil

They give good base oils the performance benefits consumers expect, such as multi-grade performance, extended drain intervals and extreme-pressure performance.

• Anti-Wear Agents chemically react to form a film barrier that prevents metal-to-metal contact and wear. They reduce friction and wear while helping prevent scoring or seizure. Wear causes friction and causes energy loss in the form of equipment-damaging heat. With Anti-wear agents reducing metal-to-metal contact, reducing friction, and lowering operating temperatures, lubricant and equipment life can be extended.

• Antioxidants reduce the tendency for oil to react with oxygen and reduce sludge buildup. Oxidaton can increase viscosity, acid content, sludge and other deposits while simultaneously depleting additives.

• Dispersants help suspend and disperse contaminants in the oil to keep engine surfaces free of sludge and deposits. They fight the build-up of corrosive acids and are most efficient at controlling low-temperature deposits. By keeping contaminants suspended within the lubricant, sludge, varnish and other carbon deposits are prevented from forming on engine parts.

• Detergents Detergents neutralize varnish and sludge to help keep surfaces clean and deposit-free. They are most efficient at controlling high-temperature deposits. Base oils possess a varying degree of ability to dissolve a solid, liquid, or gas, which assists in maintaining internal clealiness. However, commonly paired detergents and dispersants play a key role. These pairings maintain internal cleanliness by suspending contaminants, minimizing contaminant clumping and preventing contaminants from adhering to components.

• Extreme-Pressure Additives coat metal surfaces to help prevent close-contact components from seizing under extreme pressure. They are activated by high temperatures and high loads to react with the metal’s surface to form a sacrificial wear layer on components.

• Foam Inhibitors reduce the surface tension of air bubbles and causes them to collapse. Foam in an oil system can lead to poor component protection and mechanical damage. Oil viscosity, contaminants, changes in surface tension and additives can all act as catalysts to the formation of foam. Under compression, the foam heats up to extreme temperatures and generates steam within the fluid. Foam creates an insulataing layer and prevents heat from being released; the heat and water greatly limit the lubricant's effectiveness.

• Friction Modifiers can be used to give oil more ‘slippery’ characteristics. In motor oils, friction modifiers are used to increase the oil’s lubricity for the purpose of reducing friction and improving fuel economy.

• Pour-Point Depressants give high-viscosity oils good low-temperature properties to deliver better wear protection at start-up. Pour-point depressant polymers inhibit the formation of crystals to minimize low-temperature viscosity increase. Pour point does not ensure usability at such temperatures. A fluid's pour point does not indicate its lowest possible functional temperature. The usable low temperature of oil, called its stable pour point, is typically 5°F to 15°F above its indicated pour point. A fluid's stable pour point is a better indicator of low-temperature performance and protection.

• Seal-Swell Agents Their role is to help lightly swell elastomeric seals to prevent leaks. Elastomer/seal compatibilty of a lubricating fluid is extremely important in ensuring proper equipment operation. Common problems that can result from seal/oil incompatibility include degradation, shrinking or over swelling of the seals.

• Rust & Corrosion Inhibitors form a protective barrier over component surfaces to seal out water and contaminants. While most rust and corrosion inhibitors work by forming a physical barrier, some rust inhibitors function by neutralizing acids. Oxidation of metal may be referred to as either corrosion or rust. Rust describes the oxidation of iron, while corrosion describes the deterioration of other metals such as aluminum, magnesium, copper and/or copper-containing metals (yellow metals).

• Viscosity Index (VI) Improvers are long-chain polymers that help control the viscosity of multi-grade motor oils. They expand and contract as temperatures vary. High temperatures cause VI improvers to expand and reduce oil thinning; low temperatures cause VI improvers to contract and have little impact on oil viscosity. Basically, reduce the rate of viscosity change when temperatures rise or fall. VI improvers can be subject to shear conditions. Permanent shearing of VI improvers can result in psiton-ring sticking due to deposit formation, increased oil consumption and accelerated equipment wear. Because VI improvers can be subject to shear conditions, formulating an oil using little or no VI improvers can be advantageous. In addition to problems caused by shear stability, quality of VI improvers varies dramatically and cannot always be easily determined.

Like most commodities, motor oil additives are available in varying degrees of quality. AMSOIL uses only the best additives available to formulate AMSOIL synthetic lubricants.