possible sources of oil contamination, wear and deposits during use. Proper blending of additives during the manufacturing process, along with proper air and oil filtration, contribute greatly toward the survivability of motor oil.
The additives we are referring to are not aftermarket additives. These oil additives are those that an oil company blends in and are specifically designed and engineered to impart specific properties to a finished motor oil formulation. These specific oil additives cause the life cycle of motor oil to be extended and/or reduce the rate at which undesirable changes take place, while others improve properties already present in the base oil.
Motor Oil, Where it Comes From and How it’s Produced…
Motor Oil Refining
Motor oils are made from the more viscous portion of the crude oil that remains after removal by distillation of the gas and oil lighter fractions. Crude oil rarely ever is used without processing, except in some specific cases for fuel to operate power plants or for certain asphalts. In most cases, it is first separated into different fractions that require additional processing in order to begin to develop lubricating oils with specific properties, such as a 5W-30, 10W-30 or a 5W-40 diesel motor oil. The first products produced from drilling are crude oil to produce gasoline and diesel fuels, kerosene and home heating oils.
Different Crude Oil Grades
There are also several different types of crude oil depending on what part of the world it comes from. Crude oils can come in light grades, that yield primarily gasoline, to heavy black crude oil. The hydrogen carbon atom structures of the crude oils vary a great deal as do the impurities, such as sulfur or wax. Some crude oil is only suitable for manufacturing gasoline, diesel and fuel oil and by-products, while others are preferred for manufacturing lubricating oils.
The three basic types of crude oil stocks are paraffinic, napthenic and asphaltic. Lubricating oils are generally produced from paraffinic and napthenic stocks. Different types of crude stocks allow refiners to select those that, when fully refined, will provide base stocks that meet their specific needs. Keep in mind that companies use different quality base stocks to manufacture their finished products. Some companies may choose to use a very high quality base stock, in addition to carefully selected and blended additives, while others may choose a lower quality, and thus less costly, base stock combined with more chemical additives to yield a similar product.
The quality and performance of a base stock can vary significantly, even though both products may meet the same specifications. Also, keep in mind that although both products may meet the same specifications, one has no way of knowing at which end of the specification range the product will fall into and how that product meets those specifications on a continuing basis. The old saying, you get what you pay for, holds true for many petroleum products (both lubricating oils and gasoline and diesel fuel) just as it does for most other products.
The first step in processing crude oil is to remove inorganic salts and water, which can form acids during processing and damage refinery equipment. After the crude is de-salted, it is pumped through a complex series of heated pipes in order to vaporize and enter what is called a fractioning tower where groups of hydrocarbons are separated according to their boiling ranges. This occurs because the fractioning tower is at different temperatures from the top to the bottom, with the bottom being the hottest.
Light hydrocarbons, such as raw gasoline, called Naptha, are vaporized to the top of the tower and then condensed to form liquid again by cooling. The lower parts of the tower are much hotter and trap the heavier hydrocarbons such as diesel fuel, kerosene, heating fuel oil and other heavy oils, which are subsequently pumped to different fractioning towers for further processing. The products remaining in the very bottom of the fractioning tower are typically used for making asphalt for roads.
So, as you can deduce from this very simplified explanation of the crude oil refining process, motor oil is not always the prime objective. In fact, it is a by-product remaining after the valuable gasoline, diesel fuels, kerosene and home heating oils are processed. Once the crude oil is separated and further refined to a point where a specific type of motor oil can be produced, many additional oil additives are required to be blended in to produce a finished product ready to bottle and distribute. There are also many different refining processes that won’t be discussed here.
Pour Point Depressants
Petroleum motor oils have waxes and paraffin that come out of the ground with the crude oil. It is very expensive to refine out these waxes and paraffin’s. There is a process to do this, called hydroprocessing; however, average quality oils are not hydroprocessed, pour point depressants are added instead. These oil additives are required in order to obtain low pour points. They do not prevent the formation of wax crystals as temperatures decline, but rather lower the point at which wax crystals form and also restrict the growth of wax crystals.
Viscosity Index Improvers
Motor oil must not be too viscous (thick) at low temperatures in order to promote easy cold weather starting, but at the same time, it must not be too fluid (thin) at higher operating temperatures in order to prevent excessive wear and prevent excessive oil consumption. Viscosity Index Improvers (VI’s) are blended into motor oil in order to impart specific performance characteristics to the oil under these operating extremes. For example, this allows for motor oil to act like a 10-weight when it is cold but when it warms up to operating temperatures it acts as a 30-weight oil.
The determination of how well a particular motor oil meets these criteria is called the Viscosity Index (VI). VI is strictly an empirical number and indicates the effect of change in temperature on viscosity. The lower the VI, the larger a change in viscosity with temperature changes. There is a specific ASTM (American Society of Testing Materials) Test D-2270 that is used to determine the VI of a motor oil.
The problem that can occur in petroleum based motor oils with VI’s is that under heat, load and shear forces the molecules of the VI tend to change shape from a round shaped molecular structure to a straightened, or aligned, molecular structure. When this occurs, the VI’s are subject to degradation due to shear forces created inside the engine, which can cause a temporary loss of the oils specified viscosity. Under shear loads, the molecules in the VI’s align themselves in the direction of the shear stresses, so there is less resistance to flow.
As the oil cools and the shear forces are no longer present, the VI’s return to their original molecular configuration and the original viscosity is returned to the oil. Where serious problems can occur, are under extreme heat and shear loads where the molecular structure of the VI’s are permanently destroyed and will not return to their original configuration when the oil cools and shear stresses are no longer present. This is the prime reason small engine manufacturers and some diesel engine manufacturers specify a straight weight, petroleum oil with no VI’s.
In general, the greater the spread in viscosity of oil, the more susceptible the oil is to shear under load and heat due to the greater quantity of VI Improvers required to achieve the spread, such as in a 5W-50 motor oil, for example. Please keep in mind that these issues with VI’s are in relation to petroleum motor only. Synthetic multi-viscosity motor oil is extremely shear resistant.
Detergents and Dispersants
With the development of heavy-duty diesel engines, plain petroleum oil could not meet the requirements of these engines. Deposits left by the oil caused piston ring sticking and rapid wear very early on, as well as blocked oil flow passages. Soon after this began occurring, oil manufacturers started to use a soap blend in the oil, which kept internal components clean by significantly reducing the formation of deposits. Over the years, much more advanced chemicals and other oil additives were developed and used as detergents and dispersants.
The use of these detergents does not clean an engine, but rather serve to delay the formation of deposits and reduce the rate at which they accumulate. They do this by neutralizing the acidic by-products of combustion. One of the main reasons why people were told to change their oil frequently is to remove the contaminants from the oil before the oils capacity to neutralize and hold them is exceeded.
Dispersants are chemicals blended into the oil that suspend materials that can cause sludge, varnish and lacquer resulting from oil oxidation to form.
The measure of an oils ability to neutralize these acidic by-products of combustion is called the Total Base Number (TBN). It is a measure of an oils reserve alkalinity. The higher the TBN, the better an oils ability to neutralize acids. A TBN of 7 is typical for average quality gasoline engine petroleum oil. Premium quality extended drain interval synthetic oils typically have a TBN of 11-12. Petroleum and synthetic diesel oils have higher TBN values due to the increased acidic by-products of combustion created by the diesel fuel combustion process. These values can range from 8-11 up to 12-14 for premium quality diesel oils.
Most motor oil has some type of anti-foam additive blended in. This is due to the fact that petroleum oils are subjected to extreme agitation primarily due the high RPM of a rotating crankshaft and also the movement and circulation of oil in valve-train components. The action created by the oil pump and the effect of blow-by gasses mixing with the oil also causes foaming. Motor oil that foams excessively cannot perform the job of properly lubricating an engine under severe operating conditions, or even in average operating conditions.
When air bubbles form in the foam, the anti-foam additives will attach themselves to the air bubbles in the foam and cause the foam to weaken, which, in turn, causes other foam bubbles attached to each other to collapse. The anti-foam additive essentially breaks down the foam when the oil film surrounding the air bubbles is ruptured. There is an ASTM D-892 test that measures a motor oils ability to resist foaming.
Rust and Corrosion Inhibitors
Rust inhibitors are special compounds blended into motor oil that, in addition to the motor oil itself, attach themselves to internal components and prevent the formation of rust by forming a barrier that prevents water from contacting the metal surface. This additive is extremely tenacious and once it attaches itself to the component it will remain there in order to do its job, especially during engine shutdown. This additive is sacrificial in nature and does deplete with time in service.
The only way to determine if these oil additives are still present in sufficient quantity to effectively prevent rust is to perform oil analysis testing or use the specific brand/type of motor oil according to the oil manufacturers specified change intervals. There are two brands of premium quality synthetic motor oils on the market that are designed and engineered for extended drain intervals of 25,000 miles/1-year and one brand engineered for up to 35,000 miles/1-year in which, when used according to the oil manufacturers recommendations, will provide exceptional rust and corrosion prevention for the entire mileage/time interval. In order to use any motor oil past the oil manufacturers recommendations, oil analysis testing must be used.
Corrosion inhibitors are blended into motor oil and serve the function of preventing corrosion of internal engine bearings made from a mix of copper, lead, aluminum and tine. The acids formed in the oil are extremely corrosive and are a result of the combustion process of gasoline and diesels fuels, as well as the oil additives that were blended in with the fuel itself. These by-products of combustion are deposited on the cylinder wall portions that are exposed to the combustion flame front above the top of the piston and then carried into other components by the oil.
Direct blow-by is also a cause of acidic contaminants in the oil. The amount of blow-by in a particular engine is dependent on many factors, with the primary one being the effectiveness of the seal between the piston rings to the cylinder. The acids formed as a result of this will corrode internal parts such as bearings, pistons/cylinders/rings, rockers, camshafts, valves, timing gear teeth and other ferrous and non-ferrous components within the engine.
There are two primary types of corrosion inhibitor chemicals and functions: one is for the additive in the oil to chemically bond to the internal parts and provide a sacrificial barrier and the other is to actually neutralize the acids so that the corrosive potency is reduced to a level where it cannot do any internal damage. This additive depletes with time in service.
Common additives for these purposes include Zinc, Phosphorus and Zinc Diethyl Dithiophosphate (ZDDP), Calcium and Barium. Barium Sulfonates and Calcium Phenates are common chemicals that are engineered with a high amount of the alkali metals Barium and Calcium in order to provide adequate neutralization capability specifically due to the alkalinity of these metals. Sulfur content in both gasoline and especially diesel fuel are one of the primary causes of acids in motor oil.
Oxidation is the result of oxygen mixing with oil at engine operating temperatures. It is not so much the amount of oxygen absorbed by the oil that is important, but the amount of oxidation products formed. Oxidation causes an increase in oil viscosity, as well as the formation of acids, resins, lacquers and varnish on internal parts, and, especially, on pistons and piston rings. More severe oxidation occurs as engine operating temperatures increase.
The effect of varnish, resins and lacquers on pistons and piston rings can cause a decrease in the amount of heat transfer between the piston and cylinder, as well as stuck piston rings, leading to severe engine damage over a period of time. If the temperatures continue to increase to extremes, then these deposits will continue to oxidize into very hard carbon type materials. When this hard carbon material meets with combustion residues and water, sludge is formed. Sludge can do further damage, such as plug and block critical oil passageways and oil pump pick-up screens.
In order to decrease the effects of oxidation, oxidation inhibitors are used, which disrupt the chemical reaction that is responsible for the formation of the oxidation, as well as chemicals that actually decompose the oxidation products already formed. The lacquers, resins and varnish are not only formed at high temperatures by the oil, but also a low to medium operating temperatures by the fuel combustion process. There are numerous, very complex chemicals that are used as oxidation inhibitors.
Anti-wear oil additives are mainly used in order to reduce the effects of engine operating conditions when a full hydrodynamic oil film cannot be maintained, which are known as boundary lubrication conditions of slow speed and low load. These anti-wear oil additives primarily act as friction reducers that prevent metal-to-metal contact. Zinc and phosphorus are common anti-wear additives.
Under high engine speeds, high loads and operating temperatures, even though hydrodynamic lubrication is present, extreme pressure (EP) oil additives are sometimes used by certain oil manufacturers to reduce friction further and control wear. EP oil additives are also used extensively in gear lubes. The chemicals used as EP oil additives include either sulfur, phosphorus, chlorine, molybdenum disulphide or a blend of these additives depending on the specific application.
Not all motor oil manufacturers use EP oil additives as they can also have a detrimental effect on other engine operating parameters and can be highly corrosive to certain metallurgical bearing compositions and can also be incompatible with alkaline detergent oil additives.
As we can see from the article above, the better quality motor oils already have all the required oil additives to provide good service life.
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