N.C. Division of Pollution Prevention and Environmental Assistance
Re-refined Oil

Oil Additives and Definitions

Certainly, motor oil is slippery. That's what helps protect an engine's moving parts. But motor oil does much more than lubricate. It helps cool the engine, keep it clean, prevent corrosion, and reduce friction to improve fuel economy. To do all of this, refiners blend in various additives, which account for 10 to 25 percent of the product you buy.

Some of the additives found in modern oils:

  • Antioxidants: Prevent the oil from thickening when it runs hot for extended periods.

  • Detergents: Help prevent varnish and sludge on engine parts and neutralizes acid formed in engine.

  • Pour-Point Depressants: Help the oil flow in a cold engine, especially in cold weather.

  • Friction Modifiers: Strengthen the oil films and prevents unlubricated contact between moving parts.

  • Viscosity-Index Improvers: Modify the oil so its viscosity is more consistent over a wide temperature range.

  • Dispersants: Keep contaminants suspended so they don't form deposits in the engine.

  • Rust and Corrosion Inhibitors: Protect metal parts from acids and water formed in the engine.

  • Foam Inhibitors: Collapse the bubbles churned up by engine crankshaft. (Foam reduces lubricating effectiveness.)

  • Antiwear Agents: Provide lubrication when oil is squeezed from between moving engine parts.

    Additives are consumed in the normal operation of an engine. When used oil is recycled and then re-refined, it goes through a 14-stage cleaning process in which additives are integrated, restoring viscosity to meet the requirements of your automobile. Re-refined oil is approved by the American Petroleum Institute.

  • Resource: Consumer Reports July '96

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