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The following article appeared in the August, 1998, issue of Lubes 'n' Greases magazine and is reproduced here with permission and in its entirety.
Over the past years, there has been a gradual but a steady increase in advertising and marketing of supplemental engine oil additives for improving an engine's performance. The manufacturers for many of these additives -- frequently referred to as "metal conditioners" or "treatments" -- claim their products treat the internal rubbing surfaces of engine components and do not alter the engine oil's performance.
Unfortunately, anything that you introduce into an engine's crankcase becomes an integral component of the oil as it has intimate contact with all existing additives that are present.
The term "additives" used in this article encompasses all supplemental products including those identified as metal treatments, metal conditioners, or surface modifiers. One particular type being promoted is the chlorine-containing additive or "chlorinated additive," and this article offers a cautionary opinion as to their use in automotive engines.
How Chlorine Works
Chlorinated additives are primarily used as extreme pressure additives in fluids and oils for industrial systems where boundary lubrication prevails. Boundary lubrication occurs when you have high loading (and usually high temperatures) between two rubbing surfaces that essentially force out the bulk fluid leaving a thin residual or surface film remaining to provide the needed lubrication.
Under these temperature and pressure conditions, extreme pressure additives in the residual film chemically react with the metal surfaces to form a surface coating (i.e., an adherent film of metallic salts) that allows metal-to-metal contact without causing any scuffing or wear(1). This surface coating acts like a "solid lubricant" and provides needed lubrication under these conditions.
There are other "chemically active" additives in addition to chlorine typically used, such as those containing sulfur, phosphorus, combinations of these with chlorine, and other elements.
Chlorinated additives however, have and continue to be widely used in many industrial applications as chlorine tends to have a capability for chemically reacting with metal surfaces much faster than other elements due to its greater electron negativity.
Chlorinated additives such as chlorinated paraffins, for example, are widely used for satisfying the extreme pressure requirements needed for industrial cutting fluids used in metal machining, a process which is almost completely within the boundary lubrication regime. Additionally, some industrial gear systems which are not enclosed -- so-called "open gear systems" -- have continued to use industrial gear lubricants which contain chlorine additives.
Additives in Autos
Chlorinated additives were initially used in automotive gear oils in the late 1930s as extreme pressure additives for hypoid gear systems(2). The types used were lead soap-sulfur-chlorine, sulfur-chlorine-phosphorus, sulfur-chlorine, and sulfur-phosphorus-chlorine-zinc(3). Their use as extreme pressure additives for automotive gear oils continued until about the mid-1960s, when they were replaced with sulfur-phosphorus additive technology because of higher temperatures and increased performance requirements of powertrain systems.
Chlorinated additives are not used in modern, fully formulated automotive engine oils. The environment within an internal combustion engine consists of high operating temperatures, combustion and blowby gases, moisture, acid and oxidation precursors, wear debris, unburnt fuel, etc. The combination of these ingredients when combined with the catalytic effects of metallic surfaces and trace soluble metals such as copper will cause the chlorine to hydrolyze -- forming hydrochloric acid and other associated reaction products. Once generated, these acidic reaction products can cause serious internal engine corrosion problems, especially on ferrous and aluminum alloys.
Think Thrice
Before using chlorinated additives in internal combustion engines, consider the following:
First is the questionable need for any supplemental product, as currently marketed engine oils are formulated to meet all engine manufacturers' requirements.
Second is the real potential for corrosion. Although some of the currently marketed chlorinated additives for engine crankcase application may contain corrosion inhibitors in their formulation, these should be viewed as a merely short-term fix (if that) and something that cannot provide any long-term protection. As the corrosion process is generally not initially visible to the operator, it can continue until the cumulative effects induce failures causing engine malfunctions.
Think of it as a person who unknowingly has high blood pressure and continues to do all the usual, stressful things. He goes on for a time thinking all is well until the cumulative effects of his high blood pressure cause a stroke. Likewise, corrosion within an engine can be a "silent killer."
Third is the possible interaction of chlorinated additives with those additives already resent in the formulated oil. Modern engine oils are highly specialized products that have undergone a considerable amount of laboratory, engine dynamometer, and vehicle fleet testing before being marketed(4). Introducing a new additive ingredient into this carefully balanced additive package and base oil combination can only compromise and very possibly diminish the proven performance qualities of the formulated oil.
With the high electron negativity of the chlorine molecule and its strong affinity for metal surfaces, the chlorinated additive can certainly interfere with the other additives due to competing surface absorption phenomena or possibly through chemically reacting. Additionally, it has been reported that chlorinated additives can promote oil oxidation(5).
These concerns are further supported in that many military lubricating oil specifications (and some commercial specifications) either prohibit use of chlorinated additives or require chlorine to be analyzed and reported as an assurance that it is not present as an additive ingredient. Also, SAE J357 (Physical and Chemical Properties of Engine Oils) lists chlorine as a contaminant(6). Any knowledgeable oil technologist would certainly support those reasons listed above.
Although well-intentioned, introducing chlorinated additives into an engine crankcase may very well lead to serious problems down the road. Unfortunately, many of the after-market oil additive products that utilize these ingredients do not state on the container "contains chlorinated additives."
However, if the product claims to "contain no TEFLON/PTFE, graphite, solids, or molybdenum disulfide," the consumer still needs to wonder if it may contain chlorinated additives. Because of this concern, at least four currently marketed supplemental engine oil additives now claim their products to be a "non-chlorine base material."
REFERENCES:
1 Booser, E.R., CRC handbook of Lubrication--Theory and Practice of Tribology, CRC Press, Boca Raton, 1983, vol II, 301. 1.
2 Smalheer, C.V., Smith, R.K., Lubricant Additives, Lezius-Hiles Company, Cleveland, 1967, chapter 1.
3 Towle, A., "Some Factors Influencing the Performance and Selection of Driveline Lubricants," Driveline Engineering, Proceedings of Institute of Mechanical Engineering, London, 1970, 184.
4 "Motor Oil Guide," American Petroleum Institute, API Publication 1551, 8th ed., 1996.
5 Miller, r.W., Lubricants and Their Applications, 1st ed., McGraw-Hill, New York, 1993, chapter 2.
6 SAE Fuels and Lubricants Standards Manuel, 1997 ed., Society of Automotive Engineers, Warrendale, 1997, chapter 2.
Maurice E. LePera of LePera and Associates is a consultant in Woodbridge, Va., and served as associate director for fuels and lubricants at the U.S. Army's Tank-Automotive Research, Development and Engineering Center. For more information, he can be reached at 4746 Occoquan Club Dr., Woodbridge, VA 22192. Phone: (703) 590-2058. Fax: (703) 590-9413. E-mail: melepera@aol.com
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