Oil Tech: Additives

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Jul2012 27

In the previous Oil Tech Articles I explained that all motor oils on the market today consist of a base stock and an additive package. The base stock article explained the different types of base stocks, how they are classified, and the benefits and drawbacks of each. This article will focus on the other component of motor oils, the additive package.

There are many different additive types, so many it might make your head spin, but they can be categorized by the basic function: extending oil life/controlling contaminants, modifying viscosity, modifying lubricity, and conditioning seals.

There are several reasons for extending oil life. Not only is it better for the engine to keep the oil stable, it also reduces maintenance costs when the oil change intervals can be extended safely. Detergents (such as boron, calcium, magnesium, and barium) neutralize acids in the oil (a result of combustion heat and gasses) and dispersants (long-chain hydrocarbons) keep contaminants suspended in the oil. This allows the contaminants to be removed when the oil is changed instead of settling inside the engine oil passages and pan. Corrosion inhibitors (alkalines, esters, organic acids) keep the engine’s oil passages free from rust and corrosion and antioxidants (amines, phenols, sulfides) keep the oil stable and prevent oxidation (breakdown) of the oil. Oil oxidation is one of the biggest causes of sludge. Other additives whose purpose is to extend oil life deactivate wear metals, keep the oil from foaming (dimethylsilicone) and misting, and modify the wax crystals in the oil.

Viscosity modifying oil additives (acrylate polymers) allow multi-weight oils to be produced (such as 5w40) by changing the viscosity index and keeping the oil viscosity more consistent across the temperature range. This includes pour point depressants, which thin the oil at low temperatures by preventing the formation of wax crystals at low temperatures.

Some of the most critical additives for engine longevity are lubricity/friction modifiers. Friction modifiers are typically solid lubricants (graphite, molybdenum disulfide, boron nitride, PTFE, etc) that lower the coefficient of friction of the oil. One of the biggest benefits of friction modifiers is lower fuel consumption. Extreme pressure agents (molybdenum disulfide, ZDDP, esters, etc) and anti-wear agents (ZDP, ZDDP, TCP) prevent lubricated metal surfaces from contacting one another. These agents create a lubricating film which reduces wear, scuffing, and scoring. Zinc (ZDDP) and phosphorus based anti scuff additives have been limited by the American Petroleum Institute due to the potential for damaging the catalyst in modern catalytic converters. Break in additives and break in oil contain significant amounts of this type of additive, but they are designed for short-term use which allows conventional oil to be used for break in while preventing damage to valvetrain components.

Another popular oil additive is a seal conditioner. Seal conditioners prevent silicone seals from breaking down due to heat and cause gaskets and seals to swell slightly to ensure a tight seal, preventing oil leakage.

While modern engine oils contain a base stock and an additive package, which contains several different types of the additives outlined above, oil additives are available seperately. One popular aftermarket additive is BG Products MOA or “Motor Oil Additive”. BG MOA is, essentially, a concentrated mixture of friction modifiers, anti-scuff and extreme pressure agents, detergents, dispersants, and antioxidants. It is recommended for use in engines with extended oil change intervals.

For the complete series of Oil Tech posts, check out this link

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