Rock Drill Lubrication #OilChat 65

Pneumatic tools are used extensively in the mining, quarrying and construction industries. Pneumatic tools (also known as air tools)  are power tools driven by compressed air supplied by air compressors.  Air tools come in various shapes and sizes, ranging from small hand tools to jackhammers (paving breakers) and massive rig mounted units as shown on the right.

Air tools generate more power in relation to their weight than conventional power tools and they are amongst the most indestructible power tools available. Many of them, however, fail prematurely. One of the root causes for this is the use of incorrect or substandard lubricants.

Blue Chip offers a complete range of quality lubricants to keep your air tools and rock drills where they belong – in production. Included in the range are:

Compo air compressor oils are formulated to meet the most demanding requirements of both rotary and reciprocating compressors. The outstanding oxidation stability of the synthetic variants makes them ideal for air compressors operating at very high pressures and temperatures. Compo is available in all relevant viscosity grades which makes it suitable for a wide variety of applications.

Rockdrill Oil RD-C is a range of high quality lubricants designed for use in heavy duty rotary and percussion type pneumatic tools. The product line includes all universal viscosity grades making them fit for use in a vast selection of equipment and operating conditions.

Rockdrill Grease is a high performance, semi-fluid lubricant optimised for percussion-type air tools. It is particularly suitable for use as an in-line lubricant for rock drills in applications where operating conditions are severe. Rockdrill Grease extends equipment life, even in the presence of highly corrosive underground mine water.

Rockdrill Emulsion is an environmentally friendly, water-in-oil emulsion recommended for use in heavy duty pneumatic tools – rock drills in particular. Rockdrill Emulsion reduces misting to provide cleaner, safer working  conditions and improved operator comfort.

Drill Rod Grease RD-W300 is specifically designed for the lubrication and protection of rock drill drilling rods. It is formulated to control friction between the rod and the rock strata and thereby reducing rotational torque and vibration, resulting in improved productivity.

Rock drills are designed to take lots of ‘hammering’ but without proper lubrication they simply dont last. The Blue Chip rock drill product portfolio is formulated to lubricate and protect air-operated equipment effectively for extended periods of time.

For more information phone 011 462 1829, email us at or visit Our lubricant experts are at your disposal and ready to provide you with advice and answer any questions you may have.

All About AdBlue #OilChat 64

If you own a new diesel vehicle, you are likely to have to keep it topped up with a special liquid that eliminates harmful gasses being released into the atmosphere…


AdBlue is a diesel exhaust fluid used in vehicles with Selective Catalytic Reduction (SCR) technology to reduce Nitrogen Oxides (NOx) in the exhaust gases of diesel engines. Nitrogen Oxides are a family of poisonous, highly reactive gases that is formed when fuel is burned at high temperatures.

NOx emissions form smog and acid rain and is central to the formation of fine particles (particulate matter or PM) and ground level ozone, both of which are associated with adverse health effects. NOx mainly impacts on respiratory conditions causing inflammation of the airways. Long term exposure can decrease lung function, increase the risk of respiratory conditions and escalates the response to allergens.

AdBlue is stored in a separate tank from the vehicle’s diesel fuel. When the  engine is running, tiny amounts of AdBlue are squirted into the exhaust gas to convert the NOx into harmless nitrogen and water.

Many diesel cars registered after September 2015 use AdBlue to reduce emissions. If you drive an emission-compliant diesel Audi, BMW, Citroën, Jaguar, Land Rover, M-B, Peugeot or VW, it is likely to use AdBlue technology. There is often a clue in the car’s model name, which may have ‘Blue’ or ‘SCR’ in it. Owners of light and heavy commercial vehicle equipped with SCR technology and meeting the Euro IV, V or Euro VI standards will also need AdBlue.

Most AdBlue tank fillers points are situated next to the diesel filler neck, and they usually have a blue cap. Other common places for fillers include the boot and spare wheel well. If you are not sure, the owner’s handbook should tell you the location.

Good news is that AdBlue is now available at competitive prices from your trusted oil supplier. The AdBlue supplied by Blue Chip Lubricants is a bright and clear, non-toxic mixture of the purest urea available and de-ionised water. For more details please phone 011 462 1829, email us at  or visit

UTTO vs TO-4 Fluid #OilChat 63

TO-4 Fluid should not be confused with Universal Tractor Transmission Oil (UTTO).  Although both TO-4 fluids and UTTOs are designed for wet brake applications, they are NOT interchangeable since they have different physical and chemical characteristics – frictional properties in particular.

TO-4 Fluid originates from the Caterpillar TO-4 Transmission Oil specification. TO-4 has become a standard term used within industry for this specific type of additive/fluid. Construction machinery, for which TO-4 fluids are intended, is normally much bigger and heavier than agricultural equipment. A high level of friction is therefore required to ensure that these heavy machines can stop on steep inclines, such as access roads down open cast mines. This necessitates TO-4 fluids to have a high coefficient of friction.


UTTO, also referred to as Tractor Hydraulic Fluid (THF) or Transmission, Differential and Hydraulic (TDH) fluid, is mainly used in agricultural applications. They are however sometimes recommended for construction machines, such as Bell ATDs. Tractor size and weight are limited since they need to use public roads, hence less friction is required to stop agricultural equipment. UTTOs therefore have a much lower coefficient of friction than TO-4 Fluids.

A wrong fluid in wet brake applications will affect fluid/brake surface interaction and decrease braking performance with possible catastrophic consequences. If an UTTO is used where a TO-4 fluid is specified, braking efficiency will be reduced, resulting in increased stopping time and distance. Using a TO-4 Fluid where a UTTO is recommended will cause very bad vibrations and brake chatter, leading to heavy wear and failure of components.

Acquaint yourself with the fluids recommended by your equipment manufacturer, have them on hand and pay attention to tractor and equipment service intervals. If in doubt our experts are at your disposal, ready to provide you with advice and to answer any questions you may have. For more information mail us at

Automotive Gear Oil #OilChat 62

Automotive gear lubrication is a very interesting but often rather controversial subject. We have discussed the topic in previous editions of our newsletter but there still appear to be grey areas surrounding the issue. We have therefore deemed it fit to revisit the subject with specific focus on API GL-6 gear oil.

Lubricants for automotive gear applications are classified by the American Petroleum Institute (API) by means of GL ratings. For easy reference we have summarised the API classifications as follows:

API Categories GL-1, GL-2, GL-3 and GL-6 have been declared inactive even though oils may still be marketed with these designations. Performance tests associated with these categories can no longer be run because parts or test installations are not available anymore – the API GL-6 test protocol in particular.

Raison d’etre for API GL-6 surfaced in the mid 1960’s when Ford needed better protection in their pickup trucks and GM developed the revolutionary front wheel drive Oldsmobile Toronado.

The V8 powered Toronado had a differential with a very high angle of gear contact for power transmission to the front wheels.

The abnormal angle of contact was the result of a differential with a very high pinion offset (discussed in OilChat No. 14) hence a higher gear oil category had to be developed. This category was later defined as AP GL-6 and the Toronado differential was actually used in the API GL-6 test procedure.

Interesting to note is that in addition to the higher pinion offset, the 1966 and 1967 model Toronados had sun gears instead of spider gears between the axle shafts. The power packed V8 Toronados also suffered from high temperatures in the engine compartment and very high loads and pressures in the drive train.

API GL-6 level of protection is still claimed by some oil manufacturers but can no longer be evaluated since Oldsmobile stopped producing the Toronado differentials many years ago. 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 extreme-pressure performance for their vehicles.

If you have any questions regarding gear oil or any other lubricant related issues, simply mail us at Our experts are at your disposal and ready to provide you with advice and guidance

Bicycle Service Products #OilChat 61

We all know that history has the tendency to repeat itself, although very seldom precisely. Since the first two-wheeler hit the road, way back in 1817, there had been several specific historic periods of time marked by increased bicycle enthusiasm, popularity and sales. After the invention of  pneumatic tyres in 1887, the bicycle was the ultimate must-have, with females being the most ardent supporters of cycling.

It offered swift, affordable and stylish transportation that could take you anywhere you cared to go, anytime you liked and for free. Fast forward the clock about a hundred years and we saw a renewed interest in cycling, triggered mainly by an upper-class passion for health and fitness. By 1990 mountain biking was a new sport that boosted pedal-power to the flavour of the time, even more so today.

Modern bikes are a far cry from the ‘boneshakers’ of yesteryear. Nowadays MTBs are packed with state-of-the-art technology, such as carbon fibre frames, front forks with coil springs, dropper seatposts, hydraulic disc brakes, electronic gears and more. Notwithstanding this array of cutting-edge features, maintenance still plays a critical role in the efficient and reliable operation of bicycles. Blue Chip Lubricants offers a complete range of products to assist you in doing just that. Some of the key products in the range are:


Brakz is a high-performance fluid especially designed for use in hydraulic brake systems fitted to modern mountain bikes. Due to its special formulation, Blue Chip Brakz is suitable for all cycle brake systems that require mineral or synthetic based brake fluid. Brakz is dyed green for easy identification and is available in handy resealable 125 ml plastic sachets.


Chainz is specifically formulated to lubricate the chains and sprockets of both on- and off-road bicycles. The wax-based formulation provides maximum film strength and resists throw-off, even at high speeds. Blue Chip Chainz controls oil, grease and grime build up to eliminate the  formation of detrimental ‘grinding paste’. Chainz comes in 125 ml sachets.


Degreaz is a multi-purpose water-based degreasing fluid suitable for a wide variety of cleaning applications. It is environmentally friendly, biodegradable and non-flammable. It is a cost-effective solution for stubborn greasy dirt and grime that have accumulated over extended periods of time. Blue Chip Degreaz is available in convenient 250 ml plastic sachets for quick and easy use by cycling enthusiasts.


The range also includes penetrating oil spray, grease, etc. To learn more about the complete range of Blue Chip Lubricants’ bicycle service and maintenance products, phone 011 462 1829, email us at  or visit

Multigrade vs Monograde Oil #OilChat 60

Motor oil has many functions to perform in the engine, but the primary one is to reduce friction between moving parts by separating the mating surfaces with a layer or film of oil. If the oil film is not sufficiently robust to separate the surfaces, they will come into contact with one another and cause wear and possibly irreparable damage. An important indication of the ability of an oil to separate moving surfaces is the viscosity of the oil.

In simple terms viscosity is the “thickness” of a liquid. For example, water will flow more readily than honey. That is because the viscosity of honey is high compared to that of water. We can therefore say that viscosity is an indication of the resistance to flow. In common engineering sense a liquid with a high viscosity will separate surfaces better than one with a lower viscosity. There is however a fine balance between the oil being thick or viscous enough to keep the moving surfaces apart and the oil being fluid enough to be pumped effectively in the engine.

This is complicated by the fact that the viscosity of oil decreases with an increase in temperature and vice versa, therefore the temperature at which viscosity is measured must always be specified. The viscosity of lubricating oil is generally measured at 40⁰C and 100⁰C. The operating temperature of motor oil in modern engines is normally around 100⁰C and therefore the viscosity of engine oil is stipulated at this temperature as shown in the last two columns in the table below:








SAE J300 Engine Oil Viscosity Classification

Oils defined by the SAE J300 classification system, cover a single requirement only and are known as monograde oils. The higher the SAE number the thicker the oil. The lower viscosity grades have a “W” (for winter) attached to the number. These oils must also conform to sub-zero viscosity requirements to make them suitable for low temperature applications. If we draw graphs of a typical SAE 15W and SAE 40 monograde oil with viscosity (plotted as a logarithmic function) on the vertical axis against temperature (as a linear function) on the horizontal axis, we come up with the blue and red lines in the diagram below:









The SAE 15W oil will flow sufficiently at low temperatures to protect engines during startup on cold mornings but will be too thin to provide adequate wear protection at operating temperatures. Contrarily the SAE 40 oil will perform satisfactorily when the engine is hot but will be too viscous to reach moving surfaces swiftly when cold. The solution? An oil that is ‘thin’ when cold but with a viscosity similar to a SAE 40 at operating temperature. To achieve this, we add a viscosity modifier (also known as a viscosity index improver) to the oil.

A viscosity modifier (VM) is an oil additive that is sensitive to temperature. When cold the VM contracts and does not impact the viscosity of the oil. At elevated temperatures it expands to increase the viscosity of the oil. If we start off with a thin oil (for argument’s sake the SAE 15W above) as base and add sufficient VM to meet SAE 40 viscosity limits at 100⁰C we have a SAE 15W-40 multigrade oil.  Similarly there are SAE 5W-30, SAE 5W-40, SAE 10W-40, SAE 20W-50, etc.  multigrade engine oils available in the market. In summary multigrade oils provide better engine protection at low and high temperatures than monogrades because they maintain optimum viscosity over the full engine operating temperature range.

If you have any questions regarding engine oil or any other lubricant related issues, simply mail us at Our experts are at your disposal and ready to provide you with advice and guidance.

Heat Transfer Oil (Thermal Fluid) #OilChat 59

Heat Transfer Fluid or Thermal Fluid is a liquid that partakes in a heat exchange process. It moves heat (thermal energy) from one section of a system to another. Heat transfer fluids are used in countless applications and industrial processes which require heating or cooling – normally in a closed circuit and in continuous cycles. The cooling system of a vehicle is a typical example where the coolant removes heat from the engine and transfers it to the radiator to be cooled down.

Water is the most common heat transfer fluid owing to its low cost, high heat capacity and favorable heat carrying properties. The useful temperature range of water is, however, restricted by freezing at 0⁰C and boiling at elevated temperatures with the actual boiling point depending on the system pressure. For higher temperatures mineral oil is a popular alternative. Probably the most common example of an oil filled heat exchange system is the domestic oil heater.

Oil heaters consist of metal columns with cavities that are filled with the heat transfer oil. A heating element at the base of the heater heats up the oil, which then flows through the cavities of the heater by convection (rising of the hot oil). The heat is transferred through the metal surfaces to the air on the outside. The surface area of the metal columns is large thus allowing lots of air to be in contact with the heater. This permits the heat to be transferred effectively, resulting in a surface temperature which is safe enough to touch.

In larger and industrial thermal fluid systems the oil is circulated with a pump (forced circulation) rather than by convection. Heat transfer systems may be open or enclosed, but almost all large industrial systems are of the closed loop design. This limits oxidation of the oil by preventing it to come into contact with oxygen in the atmosphere. A closed loop system with a single heat source (gas-fired, oil-fired, electric, biomass-fired, etc.) may be used to supply many different heating stations simultaneously and at different temperatures. The heat transfer oil capacity of such large and complex thermal fluid systems can be hundreds of liters and it is therefore essential that the oil should have a long service life. In addition, heat transfer oils must meet a number of other requirements depending on the specifics of the application. Some of the key criteria are:

Low viscosity enables adequate fluidity and promotes heat transmission.
Good heat stability controls oxidation and prevents sludge formation.
High boiling point prevents vaporization at elevated temperatures.
Large thermal capacity enables small volumes of oil to transfer large amounts of heat.
High flash point reduces the risk of fires, particularly in open systems.

Good solvency limits deposit formation and keeps heat exchange surfaces clean.
Low volatility prevents the buildup of pressure in the circulating system.
Noncorrosive formulation protects metal surfaces against rust and corrosion.
Good heat conductivity ensures effective heat transfer between oil and heat exchange surfaces.

To meet these requirements good quality mineral based heat transfer oils are formulated with highly refined base stocks and are compounded with functional additives to enhance the performance of the final product. As a rule of thumb adherence to the following temperature guidelines will ensure long service of mineral based heat transfer oils in thermal systems with forced circulation:

All it takes to keep your thermal system operating trouble-free are a few quick maintenance steps and the correct heat transfer oil. Making the right choice will enhance efficiency and increase the life of your heat transfer system. To help you make the best decision, simply mail us at Our experts are at your disposal and ready to provide you with advice and guidance.

We would also like to make use of this opportunity to wish all our readers, customers and followers a wonderful Festive Season and a prosperous New Year. We are certainly looking forward to chat to you again in 2022.

Chainsaw Lubrication OilChat#58

A chainsaw is a portable, mechanical saw which cuts material with a set of teeth attached to a rotating chain that runs along a guide bar. Chainsaws are primarily used for wood cutting activities, such as tree felling, pruning and harvesting firewood. Chainsaws with specially designed bar and chain combinations have also been developed for special applications, such as cutting concrete during construction projects.

The origin of the chainsaw is debatable, but a chainsaw-like tool was made around 1830 by Bernard Heine, a German orthopedist. This instrument, the osteotome, had a chain with small cutting teeth on the chain links. The chain was moved around a guiding blade by turning the handle of a sprocket wheel. As the name implies, the tool was used to cut bone during medical procedures.

Most chainsaws are driven by petrol engines, although some models have electric motors powered by a battery or electric power cord. Petrol driven chainsaws are fitted with two-stroke engines since they do not require an oil sump like four-stroke petrol engines. The traditional lubrication method of mixing oil with the petrol of two-stroke engines allows it to work in any orientation, as there is not an oil reservoir that is dependent on gravity. This is an essential property for chainsaws because they are required to operate at any angle.

Engine emission standards have become more stringent over the last few years. To meet these standards modern chainsaw engines are designed to run on leaner oil/petrol ratios than older models. The result is that they run hotter.

Lower quality two-stroke oils may not be adequate to provide satisfactory protection at these elevated temperatures. Furthermore, substandard oils do not have sufficient lubricating properties and will also leave carbon residues on pistons, cylinders and exhaust ports. This causes decreased engine performance and premature failure of vital engine components. To ensure a long, trouble-free life of a modern two cycle engine, it is essential to use the quality oil recommended by the chainsaw manufacturer. For more information about two-stroke engine lubrication please refer to OilChat numbers 44 to 46.

As a rule of thumb, most two-stroke engines these days use a 50:1 fuel/oil mix. This is a mixture of 2% oil in the petrol and is equivalent to 100ml of oil in 5L of petrol. Older chainsaws and larger

models (with engine capacity generally 70 cc and more) may well require higher oil ratios and the engine manufacturer’s recommendations should always be followed. When mixing the oil and petrol use a clean airtight container intended for fuel. Not only will it prolong the shelf life of the fuel mix, but it can also help prevent spillage, permeation and evaporation.

Equally important is the lubrication of the chain and bar. Without proper lubrication the working life of these critical components will be drastically reduced. The chain and bar of almost all saws are self-lubricating. They have an oil reservoir that feeds the lubricant automatically to the bar and chain when the machine is used. If a chainsaw is operating slower than normal, or the fuel tank runs dry much quicker than it should, chances are quite good that you need to add chain bar oil – and quickly. The bar and the chain run in constant contact with each other. Without lubrication, a lot of friction that could do major damage to the chainsaw, is generated.

To be effective a chain bar oil must control wear, protect against rust and corrosion and resist throw-off. To provide the desired lubricating qualities under all operating conditions, chain bar lubricants are formulated with highly refined base oils of suitable viscosity, anti-wear and/or extreme pressure additives, rust and corrosion inhibitors and tackiness agents. Anti foam additives, pour point depressants and solid lubricants may also be included in the oil formulation if required.

Finally, if the chainsaw features a sprocket at the front end of the chain guide bar, add some grease to that as well. Simply use a grease gun to give it a couple of  shots of clean, high-quality general-purpose grease but remember to clean the lubrication hole first. Once the grease begins pushing out, stop and wipe the outside of the sprocket clean.

All it takes to keep your chainsaw running for years to come are a few quick maintenance steps and the correct lubricants. If you have any questions regarding chainsaw lubrication or any other lubricant related issues, simply mail us at Our experts are at your disposal and ready to provide you with advice and guidance.

Automotive Gear Oil Applications OilChat#14

This newsletter is in response to feedback from our readers. Following OilChat #13 we have received requests to elaborate on the composition and application of automotive gear oils; API GL-4 and GL-5 in particular. The most frequent question that comes up 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 on the left 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 in

fluenced 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.

API Automotive Gear Oil Classifications OilChat#13

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

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. Viscosity limits for automotive gear lubricants are described by the SAE J306 standard as discussed in OilChat #4.