In the early days of the automobile, engine oils were classified by viscosity grade only. By 1930 vehicle manufacturers, however, recognised that there was a need for fixed standards of lubricant quality so that cars and trucks could be sold anywhere world-wide without major modifications or embarrassing failures.

 

Consequently, lubrication problems started to occur. Oils deteriorated rapidly, wear rates increased, engines failed and performance was generally unacceptable. In the early 1900s it was discovered that the addition of chemicals, referred to as additives, could improve the performance of the mineral base oils.

The American Petroleum Institute (API) then took on the task of setting standards for engine oil. Their first attempt described three oil categories: Regular (straight mineral oil); Premium (mineral oil with oxidation inhibitors) and Heavy Duty (mineral oil with oxidation inhibitors and detergents/dispersants).

However, it was soon realised the requirements for petrol and diesel engines were different and the next API engine oil classifications defined categories for petrol (ML, MM, MS) and diesel (DG, DM, DS) engine oils.

Since then the API Engine Oil Classifications have been revised and updated on various occasions to accommodate improvements in engine designs and the ever increasing stresses placed on engine oil, and more recently to address the concern over the environmental impact of engine emissions. Currently the system includes classifications for spark ignition/petrol engines (“S” series) and for compression ignition/diesel engines (“C” Series). Following is the complete classification for petrol engine oils:

 

CATEGORY	STATUS	SERVICE
SA Before 1930	Obsolete	Category for such mild service that these oils required no additives. Originally these oils were classified “API Regular”.
SB 1930	Obsolete	Formulated to provide some antioxidant and anti-scuff properties. Because this category contained no detergent additives, they were also called “non-detergent” oils.
SC 1951	Obsolete	This category provided improved protection against low temperature sludge, deposits, rust, corrosion and wear. Previously known as “API MS”.
SD 1967	Obsolete	Engine tests for this classification also included testing the cleanliness of the positive crankcase ventilation valves during short trips and stop-and-go driving.
SE 1971	Obsolete	Oils designed for this service provided more protection against oil oxidation, high temperature engine deposits as well as rust and oxidation.
SF 1979	Obsolete	Provided improved oxidation stability and anti-wear performance. These oils also offered better protection for smaller, higher revving engines operating at higher temperatures.
SG 1988	Obsolete	Oils meeting this service category provided better control of engine wear, oil oxidation, sludge and varnish for improved engine cleanliness
SH 1993	Obsolete	These oils offered better protection than previous categories in the areas of deposit control, oil oxidation, wear, as well as rust and corrosion.
SJ 1996	Current	This category exhibited different evaporation loss characteristics, plus meeting the requirements of bench tests for wet filterability, gelation index, high temperature foaming and high temperature deposits. SJ also introduced a 0.10 mass % limit on phosphorus content for improved catalyst compatibility.
SL 2001	Current	These oils were formulated to provide better high temperature deposit control and lower oil consumption.
SM 2004	Current	Designed to provide improved oxidation resistance, enhanced deposit protection, better wear protection, and improved low temperature performance over the life of the oil.
SN 2011	Current	Improved high temperature deposit protection for pistons, more stringent sludge control and seal compatibility. Better fuel economy, turbocharger protection and emission control system compatibility.

API intentionally omitted “SI” and “SK” from the sequence of categories since SI is reserved for Système International d’Unités and SK is the brand name of a South Korean oil company.

For automotive petrol engines, the latest engine oil service category includes the performance properties of earlier categories. If an owner’s manual calls for API SJ, SL or SM oil, API SN oil will provide complete protection.

It is expected that the next API standards for petrol engine oils will be available late 2017/early 2018. Some of these next generation oils will have lower multi-viscosity ratings such as 0W-16 to reduce friction for improved fuel economy. They will also include special additive packages to reduce engine wear. These oils are being developed for high output turbocharged gasoline (petrol) direct injection (GDI) engines. API has not yet confirmed the letter designation for the new oil classification, but it will likely be “SP” (skipping “SO”).

Always consult your vehicle owner’s manual to determine what motor oil you should use, and READ THE LABELS ON THE OIL YOU BUY.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The prime functions of engine oil are to lubricate, cool, clean, protect and seal. In the early days of the automobile neat mineral oil was used to perform these functions. Improvements in engine design and engineering techniques soon lead to parts being manufactured to finer tolerances, higher engine operating temperatures, more power and increased speeds.

 

Consequently, lubrication problems started to occur. Oils deteriorated rapidly, wear rates increased, engines failed and performance was generally unacceptable. In the early 1900s it was discovered that the addition of chemicals, referred to as additives, could improve the performance of the mineral base oils.

Today engine oils may contain anything between 3% additives in a basic monograde oil and up to 30% in a superior high performance multigrade lubricant. Following is a typical composition of a modern good quality multigrade engine oil:

The base oil component of engine oils may be mineral, synthetic or semisynthetic (a mixture of mineral and synthetic stocks). Most lubricants sold today are still blended using mineral base oils. Synthetic base stocks are used whenever petroleum (mineral) based oils have reached their performance limit. Synthetic lubricants have improved high temperature characteristics and are more stable over a wide range of operating temperatures.

Additives are extensively used to improve and maintain modern oil performance. Following is a brief discussion of the additives found in reputable brands of engine oil:

Viscosity Modifiers (also called viscosity index improvers):

Are used to produce multigrade engine oils. They reduce the tendency of the oil to thicken with decreasing temperature and also resist thinning out at elevated temperatures. Viscosity modifiers (VM’s) are not used in monograde engine oils and if the oil in the above example was a monograde, the 8% VM would simply be replaced by base oil.

Detergents:

Operate on high-temperature surfaces, such as the piston-ring area and the piston under-crown, to prevent the formation of harmful deposits on these surfaces.

Dispersants:

Help to keep internal engine surfaces clean by finely suspending contaminants in the oil until they can be safely removed at the next oil change.

Antiwear Agents:

Protect metal surfaces against wear when the lubricating film breaks down. Zinc dialkyl- dithiophosphate (ZDDP) is a long-used favourite to reduce friction between metal surfaces. Some oils also contain friction modifiers to reduce friction even further but their effectiveness tends to diminish during the life of the oil.

Antioxidants:

Inhibit oxidation of the oil.  Oxidation results from exposure of the lubricant to oxygen at high temperatures. The results of such exposure accelerate aging of the oil contributing to oil thickening, sludge and deposits. Antioxidants therefore also help to keep engines running clean.

Rust and Corrosion Inhibitors:

Coat metal surfaces inside the engine to provide a protective film, preventing moisture, oxygen and acids from reaching the metal and causing rust and corrosion.

Pour Point Depressants (PPD’s):

Provide good oil flow at low temperatures. Oil contains wax particles that can congeal and reduce flow when cooled down. PPD’s modify wax crystal growth at low temperatures and oil continues to flow smoothly.

Foam Inhibitors:

Do not prevent air from mixing with the oil.  Foam inhibitors weaken the surface tension of the air bubbles that are formed allowing them to ‘burst’ more readily and thereby reducing foam.

Another critical characteristic of engine oil is its ability to neutralize acids that are formed during combustion of the fuel. The Total Base Number (TBN) measures the ability of engine oil to neutralize these acids. Detergent and dispersant additives (detergents in particular) are highly alkaline by nature and contribute to the neutralization of acids by proving the engine oil with an alkalinity reserve (TBN).

Although additive technology has improved significantly over the years, the ever increasing stress placed on the oil by modern engines demands that the oil still has to be changed at regular intervals as prescribed by engine manufacturers. Reasons for changing the oil are as follows:

To drain contaminants out of the engine when the used oil is replaced. Contaminants include dirt and dust, unburned fuel, combustion byproducts, water/coolant, wear metals and cross-contamination with other lubricants.

Additives are consumed during the service life of the oil in the engine and may get depleted.

Then why not simply put more additives into the oil?

You can’t necessarily improve the oil’s performance by increasing the additive concentration. In fact, you can make things worse. Engine oils are carefully designed and finely balanced lubrication packages that are scientifically formulated and rigorously tested before they are released in the market. By upsetting this delicate balance you will produce different results than those originally intended.  This raises another issue…supplemental oil additives.

On their own the original additives in modern engine oil are extremely effective but they can become harmful if used in combination with aftermarket or over-the-counter oil additives.  It is therefore no surprise that engine manufacturers do not approve the use of supplemental oil additives. When using a properly formulated motor oil you do not need any additional additives whatsoever. In fact, the additives you may put in can react negatively with the additives the oil company has carefully blended into the engine oil and may result in engine damage and even engine failure.

The American Gear Manufacturers Association (AGMA) has gone a step further than the ISO 3448 viscosity classification system for industrial oils (see Blog #5) in describing lubricant classifications for industrial gear lubricants. The AGMA standard provides the user with viscosity classifications as well as guidelines for minimum performance levels aimed at industrial gear oils. It aligns with the ISO viscosity standards and is verified by the American National Standards Institute (ANSI). It is published as the AGMA/ANSI 9005 standard and describes the following four types of industrial gear lubricants:

Rust and Oxidation-Inhibited Gear Lubricants:

(also referred to as R&O gear oils) are petroleum or semisynthetic based oils formulated with additive systems that protect against rust and oxidation. Some R&O gear oils also contain minute amounts of anti-wear additives. The viscosity grades for R&O gear oils are identified by AGMA numbers 0 to 13.

Compounded Gear Lubricants:

are petroleum based oils with rust and oxidation inhibitors, demulsibility additives and 3 percent to 10 percent fatty oils. These gear lubricants are frequently used in worm gear drives to provide adequate lubrication and prevent sliding wear. Compounded gear oils are identified by single-digit AGMA numbers with the suffix “Comp” from 7 Comp to 8A Comp.

Extreme Pressure Gear Lubricants:

(commonly referred to as EP gear oils) are petroleum or semisynthetic based and are fortified with multifunctional additive systems. These additive packages generally contain rust and oxidation inhibitors, EP additives, demulsifiers, antifoam agents, and in some cases solid lubricants such as graphite. AGMA numbers combined with the suffix “EP” describe these lubricants and range from 2 EP to 13 EP.

Synthetic Gear Lubricants:

are formulated with fully synthetic base stocks and are used whenever petroleum based gear oils have reached their performance limit. Synthetic gear lubricants have the advantage of improved thermal and oxidation resistance and being stable over a wide range of operating temperatures. They normally contain additives similar to those found in EP gear oils. Synthetic gear lubricants are identified by AGMA numbers with the suffix “S” from 0 S to 13 S.

The table below illustrates how AGMA gear oil viscosities correspond to ISO industrial oil viscosities:

Residual compounds 14R and 15R (asphaltic cutbacks) are not included above since these lubricants are being phased out.

In this and previous issues of OilChat we have discussed the following viscosity classification systems: SAE engine oils, SAE gear lubricants, ISO industrial fluids and AGMA industrial gear lubricants. The following chart brings all these together and provides a comparative illustration of all the various viscosity grades:

Not all viscosity grades appear on the chart as only the most commonly used grades are listed.

Viscosities relate horizontally only.

For example, the following oils have similar viscosities: ISO 150, AGMA 4, SAE 40 and SAE 90.

This may surprise you since many people think that gear oil is thicker than engine oil.

After the industrial revolution many classification systems were devised to designate viscosity grades for lubricants used in manufacturing and other industrial applications. While all of these have served useful purposes to some degree or another, it was confusing since different units were used to report viscosities such as Saybolt Universal Seconds, Redwood Seconds, Engler Degrees, Centistokes, and more.

To add to the confusion, two measures of temperature (Fahrenheit and Celsius) were used, not to mention that viscosities were specified at either 100°F or 40°C and 212°F or 100°C. This necessitated the need for a universally accepted viscosity classification system for industrial oils.

In response, the International Standards Organization (ISO) in collaboration with the American Society for Testing and Materials (ASTM), Deutsches Institut für Normung (DIN) and others formulated a common viscosity classification during 1975. The result is known as the International Standards Organization Viscosity Classification System, commonly known as ISO VG.

This classification is applicable to fluids for industrial applications, such as bearings, gears, compressor cylinders, hydraulics, turbines, etc. Viscosity values are reported in centistokes (cSt) and the reference temperature is 40°C which represents the operating temperature in machinery. The system comprises of 20 viscosity grades, ranging from 2 cSt to 3200 cSt.  This covers fluids from as thin as paraffin to oils with a consistency similar to that of syrup. The viscosity of each grade within the classification is approximately 50% higher than the viscosity of the previous grade. The minimum and maximum limits of each grade are the mid-point viscosity plus or minus 10%. For example, ISO VG 100 has a mid-point viscosity of 100 cSt at 40°C with viscosity limits 90 cSt and 110 cSt:

ISO 3448 Viscosity Classification

This system does not evaluate the quality of a lubricant and applies to no property of a fluid other than its viscosity at the reference temperature. It does not relate to those lubricants that are used primarily with automotive equipment and are identified with a SAE number.

The SAE J306 standard specifies viscosity limits for the classification of automotive gear lubricants. SAE J306 viscosity grades should not be confused with the SAE J300 viscosity grading system for engine oils (please refer to the previous blog). SAE J306 is intended for use by equipment manufacturers when defining and recommending automotive gear, axle and manual transmission lubricants and for oil marketers when labelling such lubricants with respect to their viscosity.  It is also used in Owners’ Manuals to advise operators which viscosity grade to use.

The SAE J306 classification is based on the lubricant viscosity at both high and low temperatures. The high temperature kinematic viscosity values are reported in centistokes (cSt). The low temperature viscosities are determined at sub-zero temperatures and are reported in centipoise (cP). High temperature viscosity is related to the hydrodynamic lubrication characteristics of the oil and test results must meet the 100°C viscosity limits listed in the table below. Low temperature viscosity requirements are associated with the ability of the fluid to flow and to provide adequate lubrication to critical parts under low ambient temperature conditions. The 150 000 cP viscosity value used to define low-temperature properties is based on a series of tests in a specific rear axle design. These tests have shown that pinion bearing failure has occurred at viscosities higher than 150 000 cP in the test axle. The Brookfield test method is used since it provides adequate precision at this viscosity level.

For many years the SAE J306 standard comprised four low temperature grades (SAE 70W, 75W, 80W & 85W) and three high temperature grades (SAE 90, 140 & 250). During 1998 the standard was revised to incorporate two additional viscosity grade designations, SAE 80 and SAE 85. These new grades were included to specify the viscometrics for manual transmission lubricants. Another two viscosity grades were added to the viscosity classification as part of the January 2005 update. These new grades are SAE 110 (100 °C viscosity between 18.5 and 24.0 cSt) and SAE 190 (100 °C viscosity between 32.5 and 41.0 cSt).

The need for these two grades were necessitated by the wide variation in kinematic viscosity possible within prior versions of J306 for the SAE 90 grade (100 °C viscosity between 13.5 and 24.0 cSt) and the SAE 140 grade (100 °C viscosity between 24.0 and 41.0 cSt). The effect of such wide ranges of kinematic viscosities could result in an axle being serviced with a lubricant that had a viscosity significantly lower or higher than the lubricant that the axle had been designed for, even if the same viscosity grade had been used. Prior to 2005 OEMs may also have been forced to specify a higher viscosity grade than what they actually required, because the wide range of kinematic viscosities of the next lower grade could result in customers using a lubricant with a too low kinematic viscosity.

The current J306 Viscosity Classification for Automotive Gear Oils is:

To classify the viscosity grade of automotive gear oils, a lubricant may use one W grade numerical designation, one non-W grade numerical designation, or one W grade in combination with one non-W grade. In all cases the numerical designation must be preceded by the letters “SAE”. In addition, when both a W grade and a non-W grade are listed, the W grade is always recorded first (i.e. SAE 80W-90).

A lubricant which meets the requirements of both a low-temperature and a high-temperature grade is commonly known as a multiviscosity-grade oil. For example, an SAE 80W-90 lubricant must meet the low-temperature requirements for SAE 80W and the high-temperature requirements for SAE 90. Since the W grade is defined on the basis of maximum temperature for a Brookfield viscosity of 150 000 cP and minimum kinematic viscosity at 100 °C, it is possible for a lubricant to satisfy the requirements of more than one W grade. In labelling a W grade or a multiviscosity grade lubricant, only the lowest W grade conformed to may be mentioned on the label. Thus, a lubricant meeting the requirements of both SAE 75W and SAE 85W as well as SAE 90 would be labelled as SAE 75W-90, and not SAE 75W-85W-90.

Similar to the SAE J300 grading system for engine oils, the SAE J306 standard only specifies viscosity limits for automotive gear lubricants. Other lubricant characteristics such as performance level and service classification are not considered. These will be discussed in future articles.

The earliest attempts to classify motor oils were made when automobiles first appeared. Even at this early stage, viscosity was recognized as one of the most important characteristics of oil. For this reason, the Society of Automotive Engineers (SAE), in co-operation with engine manufacturers, developed the original SAE J300 viscosity grading system for engine oils way back in 1911.

Oils were assigned numbers based on viscosities at certain temperatures. Over the years these standards were updated several times to keep in pace with engine developments and technology advancements.

It has been recognized that oil viscosity at colder temperatures, as well as at high operating temperatures, is very important in the performance of an engine. The SAE has therefore devised two separate viscosity measurement systems, one at a high temperature (100°C) and one at very low temperatures. A rotating viscometer, called a cold cranking simulator, is used to measure viscosities at temperatures as low as -35°C. Because the viscosities are measured in two different temperature ranges, the results are reported in two different units.

The first unit is the centipoise (cP). It is used to report the absolute viscosity of motor oil at low temperatures. This number indicates the ease with which the oil can flow when cold. The other unit is the Centistoke (cSt) which is used to report the kinematic viscosity of motor oil at higher temperatures.

Oils that are suitable for use in colder temperatures are identified by the letter “W” when indicating the SAE viscosity grade. These oil grades must meet maximum viscosity limits at specified sub-zero temperatures and must also meet maximum requirements for the borderline pumping temperatures at very low temperatures. Oils that are suitable for use at higher temperatures have viscosities within specified ranges at 100°C. The standards below have been used to classify engine oil viscosities for a number of years:

SAE BOO Engine Oil Viscosity Grades

If we draw graphs of typical SAE 5W and SAE 40 monograde oils with viscosity plotted as a logarithmic function on the vertical axis against temperature as a linear function on the horizontal axis, we will end up with the two solid red lines in the diagram below:

The SAE 5W oil will flow sufficiently at low temperatures to protect engines during startup on cold mornings but will be too thin to provide adequate protection at operating temperatures. The SAE 40 oil on the other hand will perform satisfactorily at operating temperatures but will be too viscous to flow sufficiently during startup on cold mornings. The solution? An oil that is ‘thin’ on cold mornings but with a viscosity similar to that of a SAE 40 at operating temperature. But how do we achieve that? With a viscosity modifier (viscosity index improver).

A viscosity modifier (VM) is an oil additive that is sensitive to temperature. At low temperatures, the VM contracts and does not impact the oil viscosity. At elevated temperatures, it expands and an increase in viscosity occurs. If we use a thin oil (let’s say the SAE 5W above) as base and add sufficient VM to meet SAE 40 viscosity limits at 100°C, we end up with a SAE 5W-40 multigrade oil – the red dotted line. Similarly, there are SAE 15W-40, SAE 20W-50, etc. multigrade engine oils available in the market. Multigrade oils provide better engine protection at low and high temperatures than monograde oils because they maintain optimum viscosity over the full engine operating temperature range.

Of particular interest is the inclusion of three new high temperature viscosity grades in the latest revision of the SAE J300 Engine Oil Viscosity Classification Standard. They are SAE 16, SAE 12 and SAE 8 (not shown in the table above). These new grades reflect the continued industry push for lower viscosity engine oils to achieve improved fuel economy. They establish specifications to standardize new lower viscosity lubricants such as SAE 5W-12, or even SAE OW-8, in the marketplace.

In most instances lubricating oil is a blend of base oil and additives with the base oil content being anything between 70 percent and more than 99 percent depending on the final application of the lubricant. Base oils may be mineral, synthetic or semisynthetic – a mixture of mineral and synthetic stocks. Most lubricating oils used globally (more than 90 percent) are blended using mineral base oils. Feed stocks from a number of streams at crude oil refineries are processed at base oil refineries to produce various viscosity grades of mineral base oils. A typical mineral base oil refinery will have the following units to produce suitable quality base oils:

• Solvent Extraction to remove undesirable aromatic (unsaturated) compounds which are unstable and cause the formation of tar, varnish and carbon in engines.
• Propane De-asphalting removes asphaltic material from the base stocks to minimize the formation of deposits in machinery, and
• Dewaxing to improve low-temperature fluidity of the base oil.

These three (extraction) conversion processes generally produce Group 1 base oils with aromatic content between 15 and 20 percent. The colour of Group 1 base oils would normally vary from a light yellow to straw. The quality of such base oils can be further improved by a number of Hydrofinishing Processes. Hydrofinishing changes the remaining unsaturated/aromatic compounds in the oil by a chemical reaction involving hydrogen and produces base oil with improved chemical stability, lower sulphur content and much lighter colour. The final quality of the base oil is determined by the severity of the application, temperature and pressure in the hydrofinishing process and will normally be classified Group 2 or Group 3 base oils. The quality and characteristics of modern Group 3 base oils approach that of synthetics.

Synthetic base oils are manufactured from chemical building blocks and excel mineral oils in viscosity index, shear stability, low and high temperature performance, oxidation stability and volatility. A major disadvantage of synthetics is that they cost approximately 3 to 5 times more than mineral oils. They therefore tend to be used in specialty applications only where the performance of mineral oil is considered unsatisfactory. Typical examples are very high temperature applications and extended oil drain intervals.

The most commonly used synthetic oil is polyalphaolefin (PAO). PAO’s are classified Group 4 base oils and are used in a wide variety of automotive and industrial applications such as engines, transmissions and hydraulic systems. The use of Group 5 base oils (typical synthetic esters) are limited to very special applications such as refrigeration compressor oils and aviation turbine lubricants. The table below shows the general differences between the various Groups.

Mineral and synthetic base oils are produced in a number of viscosity grades. For instance, low viscosity (thin) base oils would be used to produce automatic transmission fluids whilst thick, heavy ones are required to blend ISO 680 viscosity grade gear oils.

A final word of advice: avoid mixing different oil Groups. In an emergency situation, mineral oils may be mixed with PAO’s, but Group 5 synthetics should preferably not be used with any other oil Group.

All Q8Oils lubricants produced by Blue Chip Lubricants are blended exclusively from imported Q8 base oils that are manufactured from Kuwait Export Crude. Most petroleum products are derived from crude oil which, as a natural material, has a tendency to vary in type and quality depending on its source. Kuwait Export Crude is however unique, its consistency and superior quality make it the perfect feed-stock for refining high quality base oils. Q8 base oils are hydro-finished using a unique process that removes any remaining impurities rendering them clear, pure and very oxidation stable.

With complete control of our raw materials we can guarantee a consistency of product quality matched by few other companies and our customers can have complete confidence in the performance of our products.