By Kevin S. McCartney. Kevin McCartney has compiled this comprehensive list of information related to modern oil additive and supplements. This is sure to be an interesting read full of new information for anyone interested in the science behind modern automotive oils.
Boundary Lubrication and Anti-Wear Additives
When the oil between two surfaces is squeezed out, Hydrodynamic Lubrication (HL) fails and Boundary Lubrication (BL) takes over. This is when anti-wear additives come into play. Some anti-wear additives react with surface metal to provide a sacrificial oxide layer of protection. Others bond to a surface to form a similar sacrificial barrier. Either way, this boundary layer of protection is inferior to maintaining Hydrodynamic Lubrication (HL). Careful selection of proper oil viscosity will reduce the condition in which the engine shifts from Hydrodynamic Lubrication to Boundary Lubrication.
Thicker oil helps maintain HL, but it can also increase friction, oil shearing and subsequent oil break-down. Typical engines have a “sweet spot” that is large enough for the OEM recommended oil to maintain a good balance between HL and oil shearing during any normal and severe driving conditions. Extreme driving conditions that include extreme cold with short trips may require thinner oil in order to maintain proper oil flow and prevent excessive oil shearing damage. Extreme driving conditions that include continuous extreme loads and extreme oil temperatures may require much higher quality and/or thicker oil to maintain HL. Camshaft break-in is also an example of an extreme condition. 99% of all drivers are best served by staying strictly within the OEM recommendations.
Zinc Phosphate Anti-Wear Additives
Zinc dithiophosphates (ZDP) or zinc dialkyl dithiophosphates (ZDDP) are the cheapest and most commonly discussed anti-wear additives. They provide no anti-wear benefits unless Hydrodynamic Lubrication fails and the oil can no longer prevent “surface to surface” contact. Under extreme conditions when boundary lubrication takes over, the sacrificial layer “manages” wear but is consumed in the process. If sufficient ZDP/ZDDP remains in the oil, the oxide layer is quickly rebuilt.
ZDP/ZDDP is a multi-purpose additive that serves as an:
- anti-wear additive
- anti-oxidation additive
- anti-corrosive additive
ZDP/ZDDP is actually a family of compounds with similar properties. But, they are not all equal. They vary greatly in their ability to remain active in the crankcase oil during normal operation. Some of these compounds have high volatility and will “flash out” quickly leaving the crankcase oil through the PCV system. This shortens the life of the oxygen sensors and catalytic convertors. The loss of ZDP/ZDDP can also compromise critical engine protection whenever operating conditions require boundary layer lubrication.
A new generation of low volatility ZDP/ZDDP additives will become available by the end of 2010. These compounds were developed to meet the new GM Dexos and ILSAC GF-5 oil standards. Many thrifted ILSAC GF-4 oil formulas reportedly compromised critical engine protection during camshaft break-in and some other limited extreme driving conditions. Dexos and ILSAC GF-5 address this problem with a new test that insures an ability to retain enough ZDP/ZDDP in the crankcase oil to provide needed protection.
After the introduction of ILSAC GF-4, most camshaft failures where blamed on the reduced ZDP/ZDDP content of the oil. This led to increased use of ZDP/ZDDP bearing oil supplements. In some cases the supplements were mis-used to the point that ZDP/ZDDP was overdosed over a significant period of time. This caused piston ring deposits, ring sticking and cylinder scoring. ZDP/ZDDP is an effective anti-wear additive but it must be used carefully. Supplements are always riskier than using the correct fully formulated oil.
ZDP/ZDDP is a controversial compound. There is no question that during normal service it has a negative impact on catalytic converters and oxygen sensors. This is not important if other factors cause these components to fail first. But, industry wide the typical lifespan of these components has increased as the level of ZDP/ZDDP and other sources of Sulfated Ash, Phosphorous and Sulfur (SAPS) have been reduced. Other, more expensive additives can provide similar protection.
Borate Anti-Wear Additives
Borate compounds are also used as anti-wear additives. They are a possible replacement for ZDP/ZDDP. But, they appear to work best in synergy with ZDP/ZDDP. The combination of Borates and low volatility ZDP/ZDDP appears to provide any needed anti-wear protection with low enough concentrations of ZDP/ZDDP to keep everyone happy. Borates have a particular advantage in air cooled motorcycles and are common in oil products formulated for that type of service.
MoS2 Anti-Wear Additives
Molybdenum disulfide MoS2 is another anti-wear additive. MoS2 does not react with or sacrifice the surface metal. It plates out on the surface and provides a durable but slippery surface that protects the metal underneath. MoS2 serves as an anti-wear additive while also reducing friction and increasing fuel efficiency.
MoS2 is a multi-purpose additive that serves as an:
- anti-wear additive
- extreme pressure additive
- friction modifier
MoS2 has caused problems in some formulas. In rare instances the compound can come out of solution and form deposits. This is a particular problem in turbocharged applications. Test sequences within the new ILSAC GF-5 and Dexos (late 2010) oil service ratings will address this. Several oil companies have shown an ability to formulate oil products with MoS2 that are compatible with turbocharged engines. The ILSAC GF-5 and/or Dexos approvals should remove the possibility of MoS2 deposit problems in low HTHS applications. Liqui-Moly has established an excellent reputation for using MoS2 in high HTHS applications without any deposit problems.
Polytetrafluoroethylene or PTFE is commonly known as Teflon. This is a suspended solid that is the active ingredient in many aftermarket oil supplements. Claims include reduced wear and reduced friction. PTFE and other suspended solids have been shown to compromise oil flow and increase wear under some conditions. They can reduce friction but OEMS do NOT approve of their use because of the associated risks. Dupont, the highest quality source for PTFE, no longer sells PTFE for use as an oil additive or supplement. This makes any supplement containing PTFE even more questionable.
Chlorinated Paraffin’s are soluble additives that are very common in aftermarket oil supplements. They are used as extreme pressure additives and friction modifiers. They can be effective in this role. But, they can also be corrosive to some engine metals and are NOT approved by OEMs.
Antioxidants prevent or slow the natural oxidation or degradation of the base oil. These additives prevent or reduce the formation of acids, resins, lacquers and varnish. Higher grade base stocks have less need for these additives.
Corrosion additives prevent or slow engine corrosion and oxidation or rust. Calcium and Barium compounds are often used to neutralize acids. Certain driving conditions and certain engine designs consume these additives very quickly. In these applications oil life will be dramatically shortened unless more of these additives are used.
Anti-Foam additives are required to prevent aeration, bubbles and foaming. This is especially important in high performance and racing applications. Bubbles do not provide good wear protection or cooling.
Dispersants are used to keep contaminants in suspension and prevent them from clumping or coagulating. Dispersant needs vary greatly among different engines. EGR equipped diesel engines require increased dispersants to deal with soot.
Detergent additives are used to clean existing sludge, prevent new sludge formation and neutralize acid. Higher grade base stocks have less need for these additives.
Viscosity Index/Improver Additives
Viscosity Index (VI) is the term used to rate a base oil or an oil products ability to resist thickening and thinning with temperature change. These VI improvers are typically thin straight polymers, or polymers that “unwind” and straighten out at higher temperatures. This helps to maintain a more consistent viscosity of a wider range of temperatures. But, typical VI improving additives are far more fragile than the base oil and are easily sheared in half under a variety of operating conditions. HD diesel applications use VI improvers that are more durable. And, higher grade base stocks have less need for VI improvers. Some top tier synthetic oil products meet SAE 5W-30 ratings without any VI improvers.
High grade Base Stocks as Additives
Other base stocks are sometimes used as additives to improve the base oil. Group III base stocks can be added to thrifted Group I oils to meet minimum requirements while allowing them to be advertised as “part synthetic”. Group V base stocks can improve seal conditioning as well as improving the general performance of most other base stocks. This is a high quality but costly approach. Other additives are often cheaper.
PTFE and Chlorine compounds make up the vast majority of oil supplements that make dramatic claims about fuel efficiency and engine protection. Most other supplements focus on oil burning, sludge or lifter noise. They use solvents, detergents and/or viscosity enhancers. The remaining supplements that are used extensively by professional shops and technicians depend on ZDP/ZDDP to provide slight improvements at the potential expense of catalyst and oxygen sensor life. Using a correct fully formulated oil product is generally safer, cheaper and more effective than even the best supplements.
EXAMPLE: A similar real world benefit can be provided by either adding the most common professionally installed oil supplement to Exxon SuperFlo or by using Mobil Clean 5000 instead of Exxon SuperFlo. Additional benefit can be provided by upgrading further to Mobil Clean 7500. The supplement provides the least benefit for the money, and increases risks. Upgrading to a better fully formulated oil is almost always better than using a supplement. (Exxon and Mobil were selected as examples because they are part of the same company and widely available throughout the United States).