ADDITIVES

High-quality engine oil will include a number of chemical compounds known as additives. These are blended in at the refinery and fall into the following categories.

Pour point depressants help cold starting by making the oil flow more easily at low temperatures. Otherwise, the oil would tend to be a waxy substance just when you need it the most.

Oxidation and bearing corrosion inhibitors help to prevent the formation of gummy deposits which can take place when engine oil oxidizes under high temperatures. In addition, these inhibitors place a protective coating on sensitive bearing metals, which would otherwise be attacked by the chemicals, formed by oil oxidation.

Rust and corrosion inhibitors protect against water and acids formed by the combustion process. Water is physically separated from the metal parts vulnerable to rust, and corrosive acids are neutralized by alkaline chemicals. The neutralization of combustion acids is an important key to long engine life.

Detergents and dispersants use teamwork. Detergents clean up the products of normal combustion and oxidation while dispersants keep them suspended until they can be removed by means of the filter or an oil change. Foam inhibitors prevent the tiny air bubbles that can be caused by fast moving engine parts whipping air into the oil. Foam can also occur when the oil level falls too low and the oil pump begins sucking up air instead of oil (like when the kids finish a milkshake). Without foam inhibitors, these tiny air bubbles would cause hydraulic valve lifters to collapse and reduce engine performance and economy significantly.

Viscosity index improvers reduce the rate at which an oil thins out when the temperature climbs. These additives are what make multiple-viscosity oils possible. Without them, single-weight oil, which permitted easy starting on a cold morning, might thin out and cause you to lose your engine on a hot afternoon. If you use multiple-viscosity oil, it's this additive that helps your gas mileage during those short trips in cold weather.

Friction modifiers and extreme pressure additives are valuable in so-called boundary lubrication, where there is metal-to-metal contact due to the absence or breaking down of the oil film between moving parts. Friction modifiers, or anti-wear agents, deposit protective surface films that reduce the friction and heat of metal-to-metal contact. Extreme pressure additives work by reacting chemically with metal surfaces involved in high-pressure contact.