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Engine oil additives: How they prevent oxidation, corrosion, deposits, and more

May 3, 2024
Engine oils are adapting to the evolving truck market and can now include various additives to help low-viscosity motor oils provide engines the protection they need.

Today's motor oils, formulated through rigorous research, are designed with a precise balance of additives to meet the demands of modern engines, ensuring protection against oxidation, corrosion, and deposits. They adhere to the latest ILSAC GF-6A, GF-6B, and API SP specifications, which are licensed by the American Petroleum Institute (API). These specifications require motor oils to meet stringent performance specifications.

Modern engines benefit from multi-grade, low-viscosity oils like SAE 5W-30, 0W-20, and 0W-16, with API incorporating newer, even lower viscosities such as SAE 0W-8 and 0W-12 into API SP for future needs. While these “ultra-low viscosities” are not widely required in North America, they are recommended by some global OEMs whose vehicles are entering the market.

Additives in low-viscosity motor oils are crucial to providing the needed engine protection. Each additive class has a different function and helps provide engine protection. A number of additives and their purpose are outlined below:

Viscosity Modifiers – Viscosity modifiers make multi-grade engine oils possible. The viscosity of an oil changes with temperature. It is important for oil to flow when it is cold to protect the engine during startup. When the engine is operating and the oil temperature is higher, the oil should be thick enough (i.e., at a higher viscosity) to protect the engine’s highly loaded parts while driving. Viscosity modifiers change the rate at which viscosity changes with temperature and lubricate the engine from the cold-start to hot-engine operation. 

Friction Modifiers – Friction modifiers establish tough films on engine parts to reduce friction, heat generation, and metal-to-metal contact. They react chemically with metal surfaces to form highly adhesive surface coatings, which are boundary lubricants that protect the engine’s smooth metal surfaces. 

Read more: Engine oil marketers brace for new era of ‘hyper-efficiency’

Oxidation Inhibitors – Excessive engine heat causes oil oxidation, resulting in thickening of the oil. Oxidation inhibitors slow down the high-temperature oil deterioration process. Turbocharged engines, fuel-injected engines, and other engines operating at higher speeds and temperatures require motor oils to contain adequate amounts of oxidation inhibitors. 

Detergent/Dispersant Additives – Detergent/dispersants keep combustion by-products suspended in a fine form that minimizes or prevents deposits from forming in engines. The right combination of these compounds in motor oil has a very marked effect on reducing sludge and varnish deposits in gasoline engines. They help reduce deposits by dispersing contaminants in the oil and preventing them from combining and depositing within the engine. 

Pour Point Depressants – Pour point depressants keep wax crystals in the oil microscopically small and prevent them from joining together to inhibit oil from flowing properly upon engine startup. These additives are called pour point depressants because they lower the temperature at which oil will pour or flow.

Rust and Corrosion Inhibitors – The combustion process produces water and corrosive acids that can lead to rust and corrosion in an engine. Today’s motor oils contain chemical additives called inhibitors, which can neutralize or prevent rust and corrosion. 

Foam Inhibitors  Air can become entrained in an engine oil, and that combination of oil and air can cause the oil to foam. The presence of water also increases an oil’s tendency to foam. The air in oil decreases the ability of the oil to protect the engine, impairs wear protection, reduces lubrication of highly loaded components, and inhibits the use of the oil as a coolant or hydraulic oil. Foam can result in poor engine operation. Quality motor oils contain foam inhibitors that weaken the tiny air bubbles in the oil and cause them to collapse almost as soon as they form. 

Additives in motor oil are depleted as they do their jobs, so oil changes need to be completed at manufacturer-recommended intervals. Using oils that meet the manufacturer’s recommendations for SAE viscosity grade and/or API Service Category and are licensed by API will help ensure that engines are properly protected for the life of a vehicle.

About the Author

Jeff Harmening | Sr. Project Manager

Senior project manager at the American Petroleum Institute (API)

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