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Classification of Industrial Gear Oil Types

The most extensively referenced industrial oil classification is the one established by ANSI/AGMA (American National Standard Institute/American Gear Manufacturers Association) that classifies industrial gear oils where gear oils are classified into four types as shown in the following table :

① R&O gear oil is formulated to contain, as additives, rust inhibitor and oxidation inhibitor and is distributed as multi-purpose oil for various applications.
② EP gear oil contains extreme pressure agents such as S-P additive and it is used in larger quantity than any other gear oil type. In addition,
③ Compound type and ④ synthetic gear oil are used for special applications.



[AGMA Gear Oil Classification for Enclosed Gear Units for Industrial Applications]

Gear Oil Type Formulation Operating Temperature Limit
R&O Type Mineral oil containing oxidation inhibitor and rust inhibitor as additives 200℉(93℃)이하
EP Type Mineral oil containing extreme pressure agent as additive. Gear oil for enclosed gear unit uses naphthenic acid or S-P based extreme pressure agent. 160(71℃)~200℉이하
Compound Type Mineral oil containing 3~10% of fatty oil or synthetic fatty acid (generally used for worm gears) 160(71℃)~200℉이하
Synthetic Type Polyol Ester, Poly Glycol, and synthetic hydrocarbon-based synthetic oil (used for enclosed gear units designed for special operating conditions or worm gears)



[AGMA Gear Oil Classification for Semi-Enclosed Gear Units and Open Gears for Industrial Applications]

Gear Oil Type Formulation
R&O Type Mineral oil containing oxidation inhibitor and rust inhibitor as additives
EP Type Mineral oil containing naphthenic acid or S-P based extreme pressure agent as additive.
Compound Type – 희석 Type Straight mineral oil of high-viscosity grade or EP oil diluted with volatile non-flammable solvent (solvent-dilution type)



In gear lubrication, the most important performance property is viscosity and, depending on the gear configuration, number of gear teeth, operating conditions, etc.,


gear oil of appropriate viscosity needs to be selected.  As for the viscosity classification of industrial gear oils, AGMA specifies it for high-viscosity grades, too.


AGMA also adopted a viscosity number specifying kinematic viscosity from 37.8℃  to 98.9℃ as in open gear applications


ANSI/AGMA classification is used in general for viscosity classification of industrial gear oils. The following table shows the mapping between ISO viscosity classification and ANSI/AGMA viscosity classification:

Difference between Racing Car Engine Oil & Ordinary Engine Oil

1. Racing Car Engine Oil & Ordinary Engine Oil


(1) Racing Car Engine Oil Features


As racing car engines focus on high performance and high power, their engine oil requirements are getting more and more rigorous, including as a minimum:
① Excellent lubrication performance at high temperatures
② Good wear-resistance/anti-seize performance
③ Superb thermal/oxidative stability


Viscosity/temperature properties are also critical in racing car engine oil. In other words, racing car engine oil must keep the engine components appropriately lubricated when the engine rotates at high RPM and under high load (thus the oil temperature rises to a higher level).


(2) Racing Car Engine Oil vs. Ordinary Engine Oil

Racing car engine oil is designed to focus on anti-seize performance at high RPM and under high load; particularly under excessive load it features excellent thermal stability.
However, as it is not particularly resistant to oxidation, with a relatively short service life and. In particular, inferior sludge dispersion performance at low temperatures, it deteriorates faster than ordinary engine oil if it is used in ordinary vehicles (racing car engine oil is designed to be replaced for each race).


To sum up, it is recommended that racing engine oil be used in racing cars for which speed matters, and ordinary engine oil be applied to ordinary vehicles as the latter is designed to cover a wide range of applications considering various operating modes

(high-speed driving, stop & go, etc.), weather conditions (summer, winter, etc.), fuel efficiency improvement, catalyst poisoning, etc.

What is automotive gear oil ?

Automotive gear oil can be broadly divided into Manual & Automatic Transmission Oil and Differential
Gear Oil. LSD gear oil is a specialized sub-type of the differential gear oil.


[Gear Oil & Required Performance]

Type Gears Intended for Required Performance of Gear Oil Viscosity & Performance of Gear Oil
Manual Transmission Oil

-Spur Gear

-Helical Gear

-Double Helical Gear

-Fluidity at low temperature

-.Viscosity/temperature properties

-Synchro-friction property

-Thermal resistance

SAE : 75W-86W, 75W-90, 80W-90

API : GL-3, 4

Differential Gear Oil

-Hypoid Gear

-Spiral Bevel Gear

-Straight Bevel Gear

-Extreme pressure-resistance

-Anti-seize property


-Thermal resistance

SAE : 90, 80W-90

API : GL-4, 5

LSD Gear Oil

-Hypoid Gear

-Spiral Bevel Gear

-Straight Bevel Gear

-Extreme pressure-resistance

-Anti-seize property


-Thermal resistance

-Wet clutch friction property

SAE : 90, 80W-90

API : GL-5


(1) MTF (Manual Transmission Fluid)

As a manual automotive transmission employs spur gears associated with relatively mild operating conditions (Helical Gear* is used in real applications) and operates with relatively minor intensity at high speed/low loading, API GL-3 or 4 as specified in the API Gear Oil classification is typically used.


(2) Differential Gear Oil

Automotive differential uses hypoid gears exposed to severe operating conditions and it is applied with impact load in driving. Therefore,  API GL-4 or 5 single-grade gear oil designed to maintain high viscosity at extreme pressure is used.


(3) What is LSD gear oil?

Therefore, LSD gear oil is required to perform in a manner equal to or better than differential gear oil, with friction-resistance.

That is why API Category GL-5  extreme pressure-resistant oil featuring high viscosity comparable to differential gear oil is used, with FM (friction modifier) being used as additive.

In general, friction modifier delivers its required performance when LSD is in operation and prevents shattering

Marine Oil – Cylinder Oil & System Oil

There are two types of marine diesel engines: crosshead and trunk piston.


In crosshead marine diesel engines, the cylinder and crankcase are separated by a partition, and the pressure pushing the piston down is imparted to the crankshaft through the piston rod and the connecting rod.

In trunk piston marine diesel engines, the cylinder and crankcase are not separated and the pressure pushing the piston down is transmitted to  the connecting rod directly where it is again imparted to the crankcase (in a manner similar to typical automotive engines).

The crosshead variant is found in many large low-RPM 2-cycle diesel engines.
It uses a long stroke for increased torque and improves fuel efficiency using low-grade burning oil

As for the lubrication of each component in a crosshead 2-cycle marine diesel engine where the cylinder and crankcase are separated (for longer stroke),
lubricating oil should be fed separately into cylinder liner that is in contact with piston head inside the cylinder and crankcase.

Oil fed into the cylinder liner is referred to as 「Cylinder Oil」 and
the other oil supplied to lubricate each component within the crankcase is called 「System Oil」.

Lubrication Characteristics of LPG Engines & Required Performance

1. Lubrication of LPG Engine
– LPG engines employ, with minor differences, a similar lubrication system to those of gasoline or diesel engines
– Using generic gasoline engine oil is permissible under normal operating conditions.
However, under severe operating conditions involving extreme loads, the viscosity of engine oil increases,
causing bearings to wear out at an accelerated pace


2. Performance Requirements Applicable to LPG Engine Oil
– Excellent oxidative stability at high temperatures, in particular anti-NOx oxidative stability
– Prevent valve wear and tear
– Prevent deposition in the combustion chamber/spark plug/piston
– Wear-resistance/anti-scuffing performance
– Adequate ash content.


[Reference]  Required Performance of Engine Oil per Vehicle Type

Vehicle Gasoline-fired Diesel-fired LPG-fired
Fuel Gasoline Diesel LPG
Combustion temperature (thermal-resistance required) 1000℃ High (compared to gasoline) High (compared to gasoline)
NOx amount (anti-NOx oxidative stability) Low High High
Soot amount (detergent/dispersant required) Low High Almost none
Sulfur content (acid-neutralization) Low High (low in recent models) Almost none

Note: *Peak flame temperature is higher than 500~700℃

About ``Bright Stock``

“Bright Stock” refers to lube base oils of high viscosity produced by atmospheric distillation and vacuum distillation, then extracting and dewaxing solvents from residual oils, and finally hydro finishing.


Bright stock is used to make lubricating oils of the desired viscosity by mixing with lubricating oils of low viscosity (used for adjusting the degree of viscosity).

Bright stock is usually blended in lubricating oils of high viscosity such as gear oil, marine diesel engine oil, and cylinder oil.


The word ‘Bright Stock’ comes from the method of producing bright colored oils by blending naphtha with dark-colored Cylinder Stock, leaving it through to winter, extracting wax ingredients from it, and then distilling to remove the floating naphtha solution.


Bright stock is not only blending material for lubricating oils, but also a product itself.


For instance, Bright Stock made from a Pennsylvania crude oil is quenching oils with excellent performance.

Can I identify if the vehicle has problem by the color of exhaust gas?

The color of exhaust gas slightly differs from vehicles, but is usually divided into colorless, white, black, and blue-gray. Therefore the color of gas emitted from a car’s muffler shows the condition of engines and the cause of failures. Then how does the cause of failure differ according to the color of exhaust gas?


First, colorless (invisible to the naked eyes due to shimmering)

If the exhaust gas is colorless, the vehicle’s engine has no problem. It indicates that the engine works normally to burn oil. Colorless or slightly light blue colored gas represents that the engine is normal.


Second, white color

White-colored exhaust gas emitted indicates that the engine is not properly ignited due to low temperature. This white color is created by incompletely combusted fuel particles, but this phenomenon disappears if the engine temperature increases. In winter, normal engines can produce white-colored exhaust gas. This is vapor produced during combustion and it’s like white breath coming out from the mouth. Much vapor is produced if hydrogen is contained more based on the ratio of carbon (C) and hydrogen (H) in fuel. That’s why the exhaust gas from buses (CNG) or taxes (LPG) in winter look white. Sometimes the abnormally increased amount of moisture is produced from the muffler in winter. It often happens when the vapor out of emissions is rapidly cooled as a hole is made in the muffler, so it is needed to check the muffler’s state.


Third, black color

Exhaust gas has black color when thick mixture gas is supplied or relatively insufficient combustion air is provided. Black color is created as incompletely combusted carbon gas comes through exhaust gas. It is because an excess of fuel is sprayed due to the defected injection pump or air is not supplied smoothly due to the air filter blocked by foreign substances. Inspection is needed.


Fourth, blue-gray color

Blue-gray color is created due to incomplete combustion. As gasket is damaged or a piston oil ring is worn out, engine oil is inflowing to a cylinder through a crack caused by wear and burns with fuel. Here blue (additive ingredients) and grey (distillates with high boiling points) colored gas is emitted. Generally the gas emitted when engine oil burns with fuel is said to be white, but precisely it is blue gray. If the blue gray colored gas is seen, it is needed to call the car in the maintenance shop and check if there is any problem with engine system including a piston ring and a cylinder head.


Therefore it is important to do a thorough check of the vehicle with great interest and avoid excessive driving in order to maintain the vehicle in good condition for a long time.

Why is the actual capacity of automotive fuel tanks bigger than nominal capacity

“It seems like the fuel tank is filled up more than the rated capacity!!!” “It’s never been like that!!!”


Driver may have all experienced something like these. Especially when filling up the car, drivers sometimes doubt if the right amount of fuel is filled for these reasons. So it does when the amount of fuel remained and filled exceeds the capacity of a fuel tank officially indicated by automakers. However if the difference is merely 5~10 liters, this is natural. It’s because it was originally designed to be larger than the nominal capacity of a fuel tank specified in the user’s guide.


Therefore if the phenomenon above happens, do not panic and check the actual difference from the nominal capacity.


1. Nominal capacity of a fuel tank (nominal capacity)

① “Nominal capacity” is designed for passenger cars to drive *about 600 km at the speed of 80~100 km/hr on the motorways.


Nominal capacity varies depending on car models and an engine displacement because it is designed considering fuel efficiency and the weight of car body.


* About 600 km driving if it is converted into a distance on the assumption that a driver can drive 5~6 hours a day at the speed of 100 km without physical fatigue (on a basis of fueling once a day).


② It was designed with spare capacity to allow a driver to drive to the next highway service area* (the average distance between service areas is about 50~60 km) and it is about 10% of the capacity of a fuel tank.


2. Why is the actual capacity larger than the nominal capacity?

If the nominal capacity of a fuel tank is 65ℓ, the actual capacity is about 75ℓ. It’s because automobile manufacturers made the fuel tank by securing spare capacity corresponding to 10~15% of the nominal capacity1. The reason is as follows:

① It is intended to prevent VOC from being leaked in the event of volume expansion caused by an air temperature rise. If the fuel tank is filled up, the fuel is likely to overflow as the internal temperature rises to push up internal pressure.

② It is also intended to secure room for expansion to prevent the leakage of fuel when the car is parked on a slant after its fuel tank is filled up. This room is called “spare capacity for expansion.”

(Note) ¹ Maintain the reference amount of fueling LPG vehicles’ fuel tanks (85%)


LPG expands if its temperature in liquid state is raised. Therefore in case of filling the container with LPG, it is regulated to have the container’s temperature maintained below 40℃ to keep liquid LPG from exceeding 85% of container content (90% in case of a storage tank).

ACEA Standards

ACEA* is the abbreviation for Association des Constructeurs Européens d’Automobiles (European Automobile Manufacturers Association) and composed of automobile manufacturers, oil companies, and consumer groups (representative).


(Note) * Association des Constructeurs Européens d’Automobiles = European Automobile Manufacturers Association


The standards established by the ACEA are more rigorous in test items than the API standards and put emphasis on durability, and also require the high-level of environmental performance such as improving fuel efficiency and reducing harmful substances like exhaust gas.


<Overview of ACEA Standards>

* ACEA A/B = Standard for Gasoline & Diesel Engine Oils

* ACEA C = Standard for Engine Oils with After-Treatment (DPF, TWA)1 (Gasoline & Diesel Engine Oils)

* ACEA E = Standard for Heavy-Duty Diesel Oils

(Note) ¹ DPF: Diesel Particulate Filter

TWA: Three-way Catalyst – Eliminating Co, NOx, and incompletely combusted hydrocarbons


1. ACEA Standards for Light Duty Engine


2. ACEA Standards for Heavy Duty Engine

(Note) * SAPS: Sulphated Ash, Phosphorus, Sulphur

* HTHS: High Temperature / High Shear Rate Viscosity

Consumption of Engine Oil

1. Mechanism of Engine Oil Consumption

① When and where engine oil is consumed

– Flow to a combustion chamber from the space between a piston and a ring (largest amount of engine oil consumed)

– Discharge along with blow-by gas

– Consumed by the engine equipment (e.g. air compressor of heavy duty engine)

– Oil leakage

② Oil consumption mechanism

– An oil film of engine oil is formed inside the wall of cylinder, but the oil deposition burns to be released into the atmosphere after being pushed by a piston ring into a combustion chamber.

– A piston has three or four piston rings. Out of them, an oil ring serves to scrape out residual oil deposited inside the wall of cylinder.


2. Optimum Consumption of Engine Oil

① Engine oil is inevitably consumed for lubrication.

② Consumption of engine oil depends on the size of engine.

Consumption is proportional to the displacement size of an engine (The area of a piston ring groove determines the volume displaced).

③ Driving habits affect the consumption of engine oil as well as fuel

High-speed rotation and overload of an engine results in more consumption of oils.


3. Causes of an abnormal increase in engine oil consumption

① Abnormal wear of a cylinder or a piston ring.

② Scratch that occurs in a cylinder or a piston ring acts as a passage of oils.


4. Solutions

① Use the proper engine oil

② Change the engine oil at proper intervals and use the designated oil filter

③ Check the engine oil and perform maintenance before driving

④ No overloading

Relation between base oils’ viscosity and temperature

1. What is viscosity?

Viscosity is the most important property governing the functions of a fluid and a measure of “sticky property” that represents the fluidity.


Viscosity is defined as a fluid’s internal resistance to flow. As shown in Figure below, if the upper slab is moved to the right side when a fluid is filled between two slabs, the magnitude of force needed to move the slab differs depending on the type of fluid. In other words, the fluid with high viscosity requires much more forces.


Absolute viscosity gives the absolute size of the degree of stickiness that resists the direction of the substance’s motion in the state of a flowing fluid. Kinematic viscosity is a relative indicator of the optimal degree of fluidity which indicates how well the substance flows, so the smaller the value is the better the fluidity is.


And the viscosity of lube base oils is defined by the molecular size as shown in Figure below; and the bigger the molecular size is, the higher the viscosity is. The size and structure of mineral-base oils are so diverse that viscosity is determined by the average molecular size. Meanwhile synthetic base oils have the same molecular structure and size.


In case of mineral base oils, the molecular size and structure change by external factors over the period of use, leading to a viscosity change in the end. But synthetic base oils are relatively very resistant to external factors because of the same molecular size and structure (high binding energy), resulting in slowing the viscosity change.

Generally the viscosity of lubricants means the kinematic viscosity expressed in cSt and the viscosity expressed in units other than cSt is as follows:


① cSt (Kinematic Viscosity)

Strokes refer to the kinematic viscosity expressed in C. G. S and one hundredth of it is expressed in centistroke (cSt). The measured temperatures are 40℃ and 100℃ according to the ISO (International Standard Organization) Viscosity Classification, which are used universally.


②°E (Engler Viscosity)

It is measured by dividing the flow time of sample oil of 200cc by the ratio of the flow time of water at 20℃. The measured temperatures are 20℃, 50℃, and 100℃ and mostly used in Europe.


③ SUS or SSU (Saybolt Universal Seconds Viscosity)

It is measured by dividing the flow time of sample oil of 60cc. The measured temperatures are 100℉, 130℉, and 210℉ and mostly used for the viscosity of base oils (in the U.S.).


For automotive lubricants, empirical SAE Viscosity Classification (SAE Standard J 300) is used.


The reason why the viscosity is called like SAE 10W-30 or SAE 40 is because the marks used when the viscosity was measured using the Saybolit viscometer are still used.


Then, let’s take a close look at the SUS viscosity that generally indicates the viscosity of base oils. For viscosity, it is required to measure SUS using the device below and put the second before alphabet N.

For instance, if the SUS is 150 seconds, it would be 150N; and if the SUS is 500 seconds, it would be 500N. Generally if N is placed after the number, the test was done at 40℃; and BS (Bright Stock) is placed after the number, the test was done at 100℃.


If the second measured in this way is converted according to the table below, it would become cSt (centi strokes), the unit of kinematic viscosity. The converted value corresponding to 500 second in the conversion table below is approximately 100 cSt.


2. Change by viscosity temperature

The viscosity of liquid usually changes according to temperature. Especially in case of lubricants (hydrocarbons), viscosity significantly differs depending on temperature variation.

[Viscosity Index]

Viscosity Index (VI) represents the relation between the viscosity of oils and temperature. The higher the temperature is, the lower the viscosity is. In contrast, the lower the temperature is, the higher the viscosity is. A high VI means that viscosity changed little by temperature variation.


VI indicates the stability of oils against temperature variation and the method of measurement is established based on experience. It is often used to determine or distinguish base oils (paraffin base oils have high VI while naphthene base oils have low VI). This is obtained through comparison and conversion on the assumption that the VI of base oils produced from Pennsylvania crude oil with excellent viscosity-temperature characteristics is 100 and the VI of base oils produced from Gulf Coast crude oil with poor viscosity-temperature characteristics is 0.

In general, if more paraffin is contained, VI is higher and if more naphthene is contained, low temperature characteristics is excellent.

Ingredients and properties of base oil

Base oils used to produce lubricants mostly (more than 90%) consist of mineral oils refined from petroleum fraction, and include synthetic oils suitable for each use only when mineral oils are insufficient to meet the performance.


Heavy crude oil fraction is suitable for lubricants because its chemical structure satisfies the basic properties of lube base oils such as viscosity and fluidity.


Crude oil is a mixture of various compounds with the majority of hydrocarbons. Yet, it is basically classified into paraffin hydrocarbons, naphthene hydrocarbons, and aromatic hydrocarbons as shown in Figure below. They have different molecular weights and carbon numbers according to the boiling point.

The basic property of base oils is viscosity, but it is determined depends on molecular weight and by distillation out of a refining process.


The mean molecular weight of base oils such as 150N (SAE 10), 500N (SAE 30), and 150 BS is 400, 500, and 700, respectively.


However for the same mean molecular weight-viscosity, the width of molecular weight distribution varies depending on the level of the boiling point. Specifically, the base oils with wide molecular weight distribution have low flash point and high evaporability (generally the NOACK value is high).


Viscosity Index (VI) vital to base oils is a measure for the change of viscosity with variations in temperature, but it is affected by the size (ratio) of a straight-chain structure of paraffin ingredients.


The ingredients with the highest VI are n-Paraffin hydrocarbons, but those over C20 are solid at room temperature and hardly included in de-waxed base oils.


Lubricant fraction includes Hetero Cyclic Compound* containing sulfur (S), nitrogen (N), and oxygen (O) although it varies depending on crude oil, which affects the properties in various ways.


(Note) *Polar compounds such as nitrogen compound and oxygen compound which are substituted with other elements including S, N, O and Metal.


Metal in the place of carbon are eliminated through a refining process (generally during the desulfurization) since they not only have a bad influence on the surface chemical properties such as demulsibility and vesiculation even in the presence of very small amount, but also cause discoloration, effluvium, and a declined in stability.


Aromatic compounds act as a natural antioxidant and base oils having the “optimal percentage of aromatic compounds” is known for outstanding oxidation stability. However in this case, it should be noted that sulfur compounds are contained in aromatic base oils.


Solvent refining is performed under the conditions with this optimal percentage of aromatic compounds considered. But if a synthetic antioxidant is used, it is better to use base oils with little aromatic compounds and hydrogenization is a suitable refining method.


Also aromatic compounds are effective in improving the resolving capability of base oils, therefore the base oils containing a lot of aromatic compounds are used in process oils, electrical insulating oils, and compressor oils despite different purposes.