What Kind Of Additives Are In Motor Oil?

Although we often stress the importance of the base stocks contained in motor oils, of equal importance is the quality of the additives. Without anti-oxidants, anti-wear, anti-foaming agents and more, base oils would quickly degrade and turn to sludge. Designing the proper combination or package of these additives to include in the motor oil is a bit of an art form and requires a large amount of testing. We explore the components below.

Friction Modifiers
Friction modifiers have a high affinity for metal and are an essential part of any high quality additive package. Molybdenum, for example, is a popular friction modifier that reduces the surface friction of the internal engine parts.

Extreme Pressure Additives
By reacting with metal surfaces, extreme pressure additives form a protective film that can withstand high temperature applications. Boron is an excellent example.

Anti-Wear Additives
These agents prevent wear in the event of metal to metal contact. They are activated at relatively low temperatures to form a protective barrier. Zinc and phosphorus (ZDDP) are popular anti-wear additives. However, although they protect from wear, they do increase friction which is often offset with friction modifiers.

Anti-Oxidant Additives
The high operating temperatures of motor oils combined with high friction and pressure are a perfect environment for oxidation when presented with metal. Oxidation leads to an increase in viscosity and eventually the formation of sludge. Sulfur, zinc, phosphorus, copper, and molybdenum are all compounds that work as anti-oxidants.

Rust & Corrosion Inhibitors
These additives work to form a protective barrier on the surface of the metal to prevent corrosion from attacking. Organic acids and esters are excellent examples.

Detergents & Dispersants
Calcium and salt are often used as detergents and dispersants to neutralize deposits and keep them floating freely. These work with alkaline agents to neutralize acids to achieve the proper alkaline level.

Anti-Foaming Agents
Foam in the lubricant must be kept to a minimum because it promotes oxidation. Dimethylsilicone is a popular anti-foaming compound.

Pour Point Depressants
Petroleum based lubricants often use pour point depressants to help lower viscosity in cold temperatures which enables the oil to flow better. Polymethacrylate is a popular compound used for pour point depressants.

Viscosity Index Improvers
The viscosity of the oil changes with temperature. Viscosity index improvers which are often comprised of methacrylate polymers work to provide the proper viscosity in the appropriate temperature range.

As you can see, there is a complex blend of addtives required to enable a motor oil to function properly. Both laboratory and field testing are required to help determine the proper blend of additives for final inclusion in the motor oil.