One of the most frequent questions that comes up around gear oil is “Can GL-5 gear oils be used in vehicles with synchronized manual transmissions?”

Modern high performance automotive gear oils (API GL-4 and GL-5) are formulated with oxidation and rust inhibitors, antifoam agents, pour point improvers and extreme pressure (EP) additives. The most common EP additives are sulfur-phosphorus (S-P) compounds that adhere to metal surfaces through polar attraction.

When subjected to heat and/or pressure (from a collapsing lubricant film) they react chemically with the metal surface to form a tough EP film. In general, the higher the GL rating, the higher the S-P content and the higher the EP protection provided.

Traditionally the engines of motor vehicles were placed in the front with a long driveshaft transmitting power to the wheels at the back – see Figure 1 below. A differential is used to let the power from the driveshaft make a 90 degree turn so it can get to the wheels via the side shafts (axles) – Figure 2. In days gone by vehicles were designed quite high on their wheels and the position of the driveshaft was not an issue. A crown wheel (large gear) and pinion (small gear) are used in the differential to ‘bend’ the power from the driveshaft to the side shafts (Figure 3). In this configuration the axis (center) of the pinion is on the same level as that of the crown wheel.  This design, however, became a problem when the height of vehicles was reduced to make them more streamline, since lots of interior space had to be sacrificed to accommodate the driveshaft tunnel – that hump that runs from the front to the rear in the floor of the vehicle. This problem was reduced with the introduction of hypoid differentials where the axis of the pinion is set below the axis of the crown wheel (Figure 4), resulting in a lower driveshaft.

Generally, a differential with the axis of the pinion on the same level as that of the crown wheel (Fig 3) will be adequately lubricated by an API GL-4 oil although GL-5 will provide better protection.  Today, however, most rear wheel drive vehicles are fitted with hypoid differentials (Fig 4). Because of the increased sliding contact between hypoid gears, their contact pressure is higher and API GL-5 oils are required to lubricate these diffs effectively.

Most API GL-5 oils correctly claim they meet GL-4 requirements but does that make them suitable for synchromesh or synchronized transmissions? The answer is NO! They meet API Gear Oil specifications, not transmission oil requirements. The API GL-4 and GL-5 categories do not mention anything about transmission oil requirements, synchronized transmission in particular.

Synchronized transmissions are fitted with synchronizers to allow light and easy gear shifting and to eliminate that grinding sound, particularly when changing to a lower gear. Synchronizers use friction to match the speed of the components to be engaged during shifting. Slippery lubricants such as GL-5 hypoid gear oils can reduce the friction between the mating synchronizer surfaces and thereby effecting synchronizer operation negatively. In addition, synchronizers are often made of copper alloys. The way in which EP additives work can be disastrous to these ‘soft’ alloys. The S-P may attack the yellow metals chemically, causing synchronizers to fail prematurely.

Another question is why API Category GL-6 is obsolete when it offers protection from gear scoring in excess of that provided by API GL-5 gear oils? To answer this question, we need to take a trip down memory lane.  Many years ago, Ford required improved protection in certain of their pickup trucks and about the same time General Motors introduced a differential with a very high pinion offset.

This necessitated a higher gear oil service category and API GL-6 was developed to provide the greater protection needed. In fact, the GM differential was used in the GL-6 test procedure. This level of protection is still claimed by some oil manufacturers, but can no longer be tested since GM have stopped producing these diffs. A shift to more modest pinion offsets and the obsolescence of API GL-6 test equipment have greatly reduced the commercial use of API GL-6 gear lubricants. Nevertheless, some manufacturers of high performance cars still specify this level of EP performance for their vehicles.

The photo below shows a brass synchronizer that had been damaged to such an extent that it no longer “grips” its mating surface.  API GL-4 lubricants contain about half the S-P additives of their GL-5 counterparts. This means they do not react with synchronizers quite as aggressively but then they provide less wear protection for transmissions. This nonetheless is not a serious problem since there are no hypoid gear arrangements in synchronized transmissions.

What is then used in the transaxles of front wheel drive vehicles where the transmission and differential are combined in one unit? Oil selection is influenced by the transaxle design:

1. Contact surfaces of the gears are big enough to carry the load and less protection is required from the lubricant.
2. Most transaxles are designed without hypoid gears.

Another question is why API Category GL-6 is obsolete when it offers protection from gear scoring in excess of that provided by API GL-5 gear oils? To answer this question, we need to take a trip down memory lane.  Many years ago, Ford required improved protection in certain of their pickup trucks and about the same time General Motors introduced a differential with a very high pinion offset. This necessitated a higher gear oil service category and API GL-6 was developed to provide the greater protection needed. In fact, the GM differential was used in the GL-6 test procedure. This level of protection is still claimed by some oil manufacturers, but can no longer be tested since GM have stopped producing these diffs. A shift to more modest pinion offsets and the obsolescence of API GL-6 test equipment have greatly reduced the commercial use of API GL-6 gear lubricants. Nevertheless, some manufacturers of high-performance cars still specify this level of EP performance for their vehicles.

In addition to API GL specifications, synchronized transmissions and limited slip differentials often have specific frictional requirements and reference should always be made to the equipment manufacturers’ oil recommendations for these units.

The API (American Petroleum Institute) defines automotive gear lubricant service designations to assist manufacturers and users of automotive equipment in the selection of transmission, transaxle and axle lubricants based on gear design and operating conditions.

Selecting a lubricant for specific applications involves careful consideration of the operating conditions and the chemical and physical characteristics of the lubricant. The API designations also recognize the possibility that lubricants may be developed for more than one service classification.

Gear oils are classified by the API using the letters GL (abbreviation for Gear Lubricant) followed by a number to identify the performance level of the oil. The API has also issued the MT-1 service designation for certain non-synchronised manual transmissions. Only three of the seven automotive gear lubricant service designations issued by the API are currently in use due to changes in manufacturers’ recommended practices or due to the unavailability of testing hardware.

The API Lubricant Service Designations for Automotive Manual Transmissions, Manual Transaxles, and Axles are described below, followed in some instances by supplemental comments (in italics) regarding the use of these lubricants:

API GL-1 (Obsolete)

This designation denotes lubricants intended for manual transmissions operating under such mild conditions that straight petroleum or refined petroleum oil may be used satisfactorily. Oxidation and rust inhibitors, antifoam agents and pour depressants may be added to improve the characteristics of these lubricants. Friction modifiers and extreme pressure additives shall not be used.

API GL-1 lubricants are generally not suitable for most passenger car manual transmissions. However, these oils may be used satisfactorily in some truck and tractor manual transmissions. Lubricants meeting service designation API MT-1 are an upgrade in performance over lubricants meeting API GL-1 and are preferred by commercial vehicle manual transmission manufacturers.

API GL-2 (Obsolete)

The designation API GL-2 denotes lubricants intended for automotive worm-gear axles operating under such conditions of load, temperature, and sliding velocities that lubricants satisfactory for API GL-1 service will not suffice. Products suited for this type of service contain anti-wear or film-strength improvers specifically designed to protect worm gears.

API GL-3 (Obsolete)

This designation denotes lubricants intended for manual transmissions operating under moderate to severe conditions and spiral-bevel axles operating under mild to moderate conditions of speed and load. These service conditions require a lubricant having load-carrying capacities exceeding those satisfying API GL-1 service but below the requirements of lubricants satisfying API GL-4 service.

Gear lubricants designated for API GL-3 service are not intended for axles with hypoid gears. Some transmission and axle manufacturers specify engine oils for this service.

 API GL-4 (Current)

The designation API GL-4 denotes lubricants intended for axles with spiral bevel gears operating under moderate to severe conditions of speed and load, or axles with hypoid gears operating under moderate conditions of speed and load. Axles equipped with limited-slip differentials have additional frictional requirements that are normally defined by the axle manufacturer.

API GL-4 oils may be used in selected manual transmission and transaxle applications where API MT-1 lubricants are unsuitable. In all cases, the equipment manufacturer’s specific lubricant quality recommendations should be followed.

API GL-5 (Current)

This designation denotes lubricants intended for gears, particularly hypoid gears, in axles operating under various combinations of high-speed/shock load and low-speed/high-torque conditions. Frictional requirements for axles equipped with limited-slip differentials are normally defined by the axle manufacturer.

API GL-6 (Obsolete)

The designation API GL-6 denotes lubricants intended for gears designed with a very high pinion offset. Such designs typically require protection from gear scoring in excess of that provided by API GL-5 gear oils.

A shift to more modest pinion offsets and the obsolescence of original API GL-6 test equipment and procedures have eliminated the commercial use of API GL-6 gear lubricants.

API MT-1 (Current)

This designation denotes lubricants intended for non-synchronized manual transmissions used in buses and heavy-duty trucks. Lubricants meeting the requirements of API MT-1 service provide protection against the combination of thermal degradation, component wear, and oil-seal deterioration, which is not provided by lubricants in current use meeting only the requirements of API GL-4 or GL-5.

API MT-1 does not address the performance requirements of synchronized transmissions and transaxles in passenger cars and heavy-duty applications.

Automatic or semi-automatic transmissions, fluid couplings, torque converters, and tractor transmissions usually require special lubricants. Consult the equipment manufacturer or your lubricant supplier for the proper lubricant for these applications.

The API Automotive Gear Oil Classifications only specify performance level and service designation.

Motor oil is a lubricant used in internal combustion engines to reduce friction and provide essential protection to engine components. There are several types of motor oil available, each with its own specific functions and characteristics.

Here are some common types of motor oil:

1. Conventional Motor Oil: Conventional motor oil is a basic lubricant derived from crude oil. It provides standard engine protection and is suitable for most common vehicles under typical driving conditions. Conventional oil needs to be changed at regular intervals.
2. Synthetic Motor Oil: Synthetic motor oil is manufactured using chemically engineered compounds. It offers better performance and protection than conventional oil, especially in extreme temperatures and demanding driving conditions. Synthetic oil has a longer lifespan and provides improved lubrication and engine cleanliness.
3. High Mileage Motor Oil: High mileage motor oil is specifically formulated for vehicles with higher mileage, usually over 75,000 miles. It contains additives that help reduce oil burn-off, prevent leaks, and minimize engine wear in older engines.
4. Synthetic Blend Motor Oil: Synthetic blend oil is a mixture of conventional and synthetic oils. It offers some of the benefits of synthetic oil at a more affordable price point. Synthetic blend oil provides improved performance and protection compared to conventional oil but not as much as full synthetic oil.
5. Racing Motor Oil: Racing motor oil is designed for high-performance racing engines that operate under extreme conditions. It has excellent heat resistance, superior lubrication properties, and enhanced protection against wear and deposits. Racing oil is not typically recommended for regular passenger vehicles.
6. Diesel Motor Oil: Diesel motor oil is specifically formulated for diesel engines. It contains additives that can handle the higher operating temperatures and pressures of diesel engines. Diesel oil provides enhanced protection against soot, deposits, and wear common in diesel engines.

It’s important to note that the recommended type of motor oil for a specific vehicle can be found in the vehicle owner’s manual. The manufacturer’s recommendations take into account factors such as the engine design, operating conditions, and maintenance requirements of the vehicle.

The ACEA Oil Sequences describe, amid others, “E” category service-fill oils for heavy duty diesel engines. These sequences define the minimum performance level for engine oils to meet ACEA requirements. Performance parameters other than those covered by the sequences or more stringent limits, may be specified by individual engine manufacturers – hence OEM specifications such as Mercedes-Benz 228.3, Volvo VDS-3, etc.

The ACEA Oil Sequences are subject to constant development to stay abreast of new engine designs, the increasing use of biofuels and more stringent emission requirements.

Each new issue of the sequences may exclude a previous sequence or include a new one, incorporate an increase in severity for an existing sequence or a change in testing method. As new editions are published older editions are withdrawn. The table below summarises the changes that have occurred since the first ACEA Oil Sequences were introduced in 1996.

E4: Stable, stay-in-grade oil providing excellent control of piston cleanliness, wear, soot handling and lubricant stability. It is recommended for highly rated diesel engines meeting Euro I, Euro II, Euro III, Euro IV and Euro V emission requirements and running under very severe conditions, e.g. significantly extended oil drain intervals according to the manufacturer’s recommendations. It is suitable for engines without particulate filters, and for some EGR (Exhaust Gas Recirculation) engines and some engines fitted with SCR NOx (Selective Catalytic Nitrogen Oxides) reduction systems.

UHPD (Ultra High Performance Diesel) category and the highest level of engine oil performance in the global heavy duty diesel market. Mostly SAE 10W-40 formulated with Group III base oils. Extended drain oils suitable for use in vehicles without a DPF (Diesel Particulate Filter). 

E6: Stable, stay-in-grade oil providing excellent control of piston cleanliness, wear, soot handling and lubricant stability. It is recommended for highly rated diesel engines meeting Euro I, Euro II, Euro III, Euro IV, Euro V and Euro VI emission requirements and running under very severe conditions, e.g. significantly extended oil drain intervals according to the manufacturer’s recommendations. It is suitable for EGR engines, with or without particulate filters, and for engines fitted with SCR NOx reduction systems. Designed for use in combination with low sulphur diesel fuel.

UHPD category and the highest level of engine oil performance seen in the global heavy duty diesel market. Mostly SAE 10W-40 formulated with Group III base oils. Extended drain low SAPS oils suitable for use in vehicles with or without a DPF.

E7: Stable, stay-in-grade oil providing effective control with respect to piston cleanliness and bore polishing. It further provides excellent wear control, soot handling and lubricant stability. It is recommended for highly rated diesel engines meeting Euro I, Euro II, Euro III, Euro IV and Euro V emission requirements and running under severe conditions, e.g. extended oil drain intervals according to the manufacturer’s recommendations. It is suitable for engines without particulate filters, and for most EGR engines and most engines fitted with SCR NOx reduction systems.

SHPD (Super High Performance Diesel) tier of mainly SAE 15W-40 engine oils designed for use in medium severity operations. Suitable for use in vehicles without a DPF. Often combined with API CI-4. 

E9: Stable, stay-in-grade oil providing effective control with respect to piston cleanliness and bore polishing. It further provides excellent wear control, soot handling and lubricant stability. It is recommended for highly rated diesel engines meeting Euro I, Euro II, Euro III, Euro IV, Euro V and Euro VI emission requirements and running under severe conditions, e.g. extended oil drain intervals according to the manufacturer’s recommendations. It is suitable for engines with or without particulate filters, and for most EGR engines and for most engines fitted with SCR NOx reduction systems. Designed for use in combination with low sulphur diesel fuel.

SHPD tier of mainly SAE 15W-40 engine oils designed for use in medium severity operations. Suitable for use in vehicles with and without a DPF. Often combined with API CJ-4. 

Claims against the ACEA Oil Sequences can be made on a self-certification basis. ACEA, however, requires that any claims for oil performance relating to these sequences must be based on credible data and controlled tests in accredited test facilities.

It is expected that new ACEA Oil Sequences will be issued during the third quarter of 2016. ACEA 2016 marks the first update since 2012, a break from the specification’s typical biennial update schedule. So what are some of the sequence changes that we can expect to see in ACEA 2016?

Biofuels: New fuel alternatives are becoming increasingly prominent, particularly the use of biodiesel fuels for the heavy duty market. These fuels can lead to increased oxidation, degradation and thickening of the oil. ACEA 2016 may therefore include new tests to assess lubricant effectiveness to prevent oxidation and deposit formation.

Seal Materials: Modern engines have introduced new elastomer sealing materials, necessitating an update of the seal test methods in ACEA 2016.

Soot: A new test may possible be added to assess oil resistance to soot-related thickening and deposits in diesel engines. The expected test will reflect the cleaner operation of modern low-soot heavy duty diesel engine oils.

In summary, modern diesel engines are being forced to become more fuel efficient, less polluting, and longer lasting. Subsequently their lubrication needs have changed dramatically since 2012. In addition, oil change intervals are being extended and the use of biodiesel is increasing. These changes require the use of superior heavy duty diesel engine oils. ACEA 2016 is expected to address all these issues and it is therefore not surprising that its pending release is anticipated globally with great interest.

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

ACEA is the abbreviation for the Association des Constructeurs Européens d’Automobiles or the European Automobile Manufacturers’ Association in English. Among many other activities ACEA defines specifications for engine oils on behalf of the major vehicle manufacturers in the European Union.

The ACEA Oil Sequences were introduced in 1996 when they superseded the former CCMC (Committee of Common Market Automobile Constructors) specifications for engine oils. The ACEA Oil Sequences are the European counterpart of the API Engine Oil Classification System.

There are three principal categories within the ACEA Oil Sequences – “A/B” for petrol and light duty diesel engine oils, “C” for light duty catalyst compatible oils and “E” for heavy duty diesel engine oils. In this blog the ACEA Oil Sequences for petrol and light duty diesel engines will be discussed. However, before this is done a few terms that are used in describing the Sequences need to be explained:

The current ACEA Oil Sequences were introduced in 2012 and may be condensed as follows:

CATEGORY	STATUS
SAPS:	(Sulphated Ash, Phosphorus, Sulphur) Phosphorus and sulphur comprise a significant portion of the additive content of engine oil. Sulphated ash is not added to oil; it is the result of additives in the oil leaving an ash residue when the oil is burnt under prescribed laboratory conditions.
DPF:	(Diesel Particulate Filter) A device designed to remove diesel particulate matter or soot from the exhaust gas of a diesel engine.
TWC:	(Three Way Catalyst) A catalytic converter that reduces the harmful Nitrogen Oxides, Carbon Monoxide and Unburned Hydrocarbons in the exhaust gas of (mainly petrol) engines.
HTHS:	(High Temperatre/High Shear rate viscosity) HTHS is indicative of the resistance of engine oil to flow in the tight tolerances between fast moving components in hot engines. It influences fuel consumption and wear in high shear regimes in an engine, such as those existing in piston ring/cylinder wall interface and the valve drive train. Lower HTHS viscosity generally means thinner oil which can improve fuel economy. Lower HTHS viscosity, however, usually comes at the expense of wear protection and therefore low HTHS oils are not suitable for use in all engines.

The current ACEA Oil Sequences were introduced in 2012 and may be condensed as follows:

ACEA A/B : Petrol and diesel engine oils

A1/B1 Fuel efficient oil for use at extended drain intervals in petrol and light duty diesel engines designed to use low friction, low viscosity and low HTHS oils. Unsuitable for use in some engines.

A3/B3 Intended oil for use in high performance petrol and light diesel engines and for extended drain intervals where specified by the engine manufacturer.

A3/B4 Intended for use in high performance petrol and direct injection diesel engines, but also suitable for applications described under A3/B3.

A5/B5 Fuel efficient oil for use at extended drain intervals in high performance petrol and light diesel engines requiring low friction, low viscosity and low HTHS oils. Unsuitable for use in some engines.

ACEA C : Catalyst compatibility oils

C1 Fuel efficient oil intended for vehicles with DPF and TWC. Formulated for high performance petrol and light diesel engines requiring low friction, low viscosity, low SAPS and low HTHS oils. These oils have a SAPS limit of 0.5% and are unsuitable for use in some engines.

C2 Fuel efficient oil intended for vehicles with DPF and TWC. Formulated for high performance petrol and light diesel engines designed to use low friction, low viscosity and low HTHS oils. These oils have a SAPS limit of 0.8% and are unsuitable for use in some engines.

C3 Fuel efficient oil intended for vehicles with DPF and TWC. Formulated for high performance petrol and light diesel engines designed to use low HTHS oils. These oils have a SAPS limit of 0.8% and are unsuitable for use in some engines.

C4 Fuel efficient oil intended for vehicles with DPF and TWC. Formulated for high performance petrol and light diesel engines requiring low SAPS and low HTHS oils. These oils have a SAPS limit of 0.5% and are unsuitable for use in some engines.

Note: Oils with a 0.8% SAPS limit may be referred to as mid SAPS.

To meet the stringent requirements of the above ACEA Oil Sequences, engine oils must pass fourteen laboratory and ten engine tests. Hence oils that conform to these ACEA standards are formulated with superior additive packages – even more so when the oil needs to meet API requirements as well. For instance, a well formulated engine oil can conform to ACEA A3/B4/C3 as well as API SM/SN. It is, however, not always possible for an oil to meet both ACEA and API standards. To illustrate, it is unattainable for an ACEA A5/B5/C1 performance level oil to meet API SM/SN, because A5/B5/C1 requires a maximum phosphorus limit of 0.05% whilst SM/SN specifies a minimum level of 0.06%.

Since the first ACEA Oil Sequences were introduced in 1996 new specifications were issued in 1998, 1999, 2002, 2004, 2007, 2008, 2010 and 2012. It is therefore obvious that the next issue of the ACEA Oil Sequences is now long overdue. Reasons for this delay are the replacement of obsolete tests with new ones to reflect engine technology advancements and also to address the complications associated with the increasing use of biofuels. It is expected that the new sequences will be issued during the second half of 2016 and that the new release may, among other changes, comprise the removal of A1/B1 and the introduction of a C5 category.

The ACEA Oil Sequences represent some of the most significant performance standards of the lubricant industry. Their influence and importance extend beyond Europe and since the pending update is a major step for the global lubricant industry, it is anticipated with great interest.

In conclusion it should be mentioned that ACEA itself does not test or approve any oils. They set the standards and oil manufacturers are responsible for having their oils tested in accordance to the prescribed standards. They may then make performance claims for their products, provided such products satisfy the relevant ACEA requirements.

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

 

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.