The common chemical compound used as an anti-wear agent is ZDDP or Zinc Diaikyldithiophosphate. ZDDP is the anti-wear agent of choice among formulators because of its overall cost effectiveness, i.e, it works as both an anti-wear agent and an antioxidant

The fact remains that there is much to be gained from incorporating extreme pressure agents in engine oil formulations. There is no argument that extreme pressure conditions do indeed exist in an engine during the course of normal engine operations. This is especially true for modern engines with tight tolerances. To disregard this in formulation works is a great disservice to the motoring public, industry and the environment.

Tribology recognizes that the actual engineering surfaces of sliding metals are only 10% to 20% of the actual geometric surfaces. Under extreme magnification, what appears to be a smooth metal surface to the naked eye is actually a landscape of microscopic "hills and valleys" or asperities. The engineering surface, or the 10% to 20% of the geometric surface, is the actual surface in contact with the same engineering surface of another metal. If the "valleys" are covered with a film, known as a Tribochemical Film, such in that the area of the engineering surfaces are increased, the structural load bearing capacity of the sliding metals can be significantly increased.

Furthermore, the "hills" that are actually weld points can be smoothed out and effectively reduce the "drag" or coefficient of friction between the sliding surfaces.

Even under boundary lubrication conditions and extreme pressure when the oil film can no longer offer any protection, the Tribochemical Film can actually substitute for the lost oil film and protect the sliding metals from welding, deformation or abrasion.

In the past, a number of chemicals have been used to create this film. The conventional chemicals used in engine oils are based on sulfur and phosphorus chemistries. These chemistries produce weak films. Previously referred to, ZDDP is a weak extreme pressure agent because it is easily abraded during boundary lubrication conditions and is easily depleted because of its additional role as an antioxidant. Furthermore, it is now under close scrutiny for its toxicity and poisonous effects on catalytic converters, thus its permissible amounts in formulations are being limited.

Others use graphite and other solid materials such as Teflon and micro-metal powders suspended in oil, making unsubstantiated claims to their effectiveness while ignoring the tendency for these solids to settle out of suspension and/or agglomerate in oil passageways. Prior to banning its use by the United States, highly toxic lead naphthenate was also marketed.

The most sensationalized additives to date are the chlorinated paraffins and related products found in late night T.V. "Infomercial" offerings. These are very strong extreme pressure agents that readily decompose for chlorine to react with metals to form metal chloride films. While effective as an extreme pressure agent, there are a number of serious problems associated with such materials. First of all, chlorinated hydrocarbons work as extreme pressure agents through the reaction of chlorine with iron to form ferric chloride films under critical pressure and temperature. This leaves the decomposed hydrocarbon portion deficient in electrons turning them into sludge precursors. Excess chlorine released during the decomposition reacts with water in the oil to form hydrochloric acid which in turn accelerates the depletion of the alkaline reserves of the oil. Depletion of the alkaline reserve necessitates an early oil change, increasing stress on the environment by adding to the amounts of waste oil in circulation.

Secondly, used oil recyclers have problems processing used oil with chlorine content. Chlorine naturally evolves hydrochloric acids that corrode fractionation towers during processing.

Thirdly, government regulators are seriously looking at chlorinated paraffins and similar materials for possible regulation. Already, the National Toxicology Program has determined that certain chlorinated paraffins are carcinogenic. Partial oxidation of chlorinated hydrocarbons may form dioxin which is extremely carcinogenic.

It must be said that the right kind of chlorinated materials can be properly incorporated into an engine oil formulation in order to take advantage of the extreme pressure property while eliminating the side effects of their decomposition products. However, the overall formulation must be done such that the standard additive package is not compromised and unwanted partial oxidation and decomposition products are not formed. Experienced oil formulators have successfully used chlorine in railroad engine oils and in synthetic oil formulations. Unfortunately, most compounders of chlorinated aftermarket additives resort to sensationalism instead of sound chemistry. Some in fact recommend treatment rates up to 20%, thereby compromising 20% of the required standard additive package as mandated by an appropriate API rating.