The formulation of the various types of lubricating oils vary significantly depending on their application. Due to the wide variety of applications in which oils are used, there are many different formulations for oils. Machine manufacturers generally designate the oil formulations that are suitable for their equipment. Why?

The many functions of oils in their application and the aimed high machine performance requires the optimal oil formulation matched for its application. A brief discussion on oil functions and requirements.

Industrial oils
Nine functions of engine oils

The formulation of the various types of lubricating oils vary significantly depending on their application.
Industrial oils anti oxidant
rust inhibitor
foam inhibitor Demulsifier Anti Wear additive EP-additive
Circulating oils x x x    
Hydraulic oils x x x x  
Gear oils x x x x x
Compressor oils x x x x  
Grease x     x x

The main functions / requirements of industrial oils in their application:

Circulating oils and Turbine oils
A typical system requires bearing lubrication, remove of heat through circualtion, serve as hydraulic oil, lubricate gears. Performance requirements are:

Hydraulic oils
A typical system includes a reservoir for the hydraulic fluid, a pump, transfer channels, and return channels to the reservoir.

Gear oils
These oils provide protection to different types of industrial gears which are often operated under high contact pressures and / high speed. There are many combinations of gear types and materials. For example worm gears interact by predominantly sliding motion whereas spur gears operate by a combination of rolling and sliding. Therefore, the requirements for gear oils varied. Lightly loaded spur gears require an oil with only rust and oxidation inhibiters while heavy loaded gears require oils with high levels of EP additives. In the case of worm gears, their action is almost all sliding and not heavily loaded. Smaller worm gears therefore may be made of bronze for better sliding wear resistance and may be lubricated by an oil with friction modifier. In these applications friction modifiers can be more effective than sulfur-containing EP additives, which might promote corrosion of bronze worm gears. For large, slow moving gears an adhesive high viscosity lubricant is required. In applications where industrial gear oils are used in environmentally sensitive areas such as forest and near waterways, biodegradable gear oils based on natural and synthetic esters have been developed.

Compressor oil
The formulations of compressor oils vary significantly depending on the type of compressor, reciprocating and rotary gas compressors and the type of gas being compressed. In reciprocating compressors lubrication include the crankshaft, bearings, connector rod, wrist pins, pistons, piston rings, cylinders and valves. Rotary compressors require lubrication of bearings, seals and shafts. High pressure reciprocating compressors require lubricants stable for high temperatures, usually synthetic esters. Rotary vane compressors require lubricants that minimize vane wear, usually synthetic PAO's due to their good thermal stability and lower cost relative to synthetic esters. Compressor manufacturers generally designate the compressor oil formulations that are suitable for their equipment.

Cutting Oils
The main functions of a cutting oil are to lubricate or reduce friction between the tool and the work piece, and to act as a coolant by rapidly removing heat generated at the tool-work piece interface.

Soluble cutting oils are mixed with water in proportions of 3 to10%. They are used where rapid heat removal is a major requirement. Usually formulated with emulsifiers, rust inhibitors, and EP additives.

Insoluble cutting oils are used in operations involving tough cutting such as tapping, threading, and broaching. Lubricity and anti-weld characteristics are important characteristics of this cutting oil.

Chain oil
These oils are formulated to lubricate saw chains, and should provide the following benefits:

An unbroken film of lubricant between chain links and bars.
Anti-wear characteristics to prevent chain and bar wear.
Prevent corrosion of the chain.


Nine Functions of Engine Oils

The automobile industry is the major user of lubricants. Engine designs have been continually improved to reduce weight, increase fuel economy, increase power output, and at the same time meet environmental emission guidelines. Research is ongoing to formulate lubricants to meet the demands of the redesigned engines. In general, a lubricant must perform nine functions for the efficient operation of the engine.

1. Permit Easy Starting
An engine oil must be thin enough when first starting the engine to allow for sufficient cranking speed. The oil must then be able to flow immediately to lubricate vital engine components. Most of the engine wear occurs at start-up before the oil can reach all the engine parts. As the engine is heated, the oil must not become too thin and be unable to provide adequate engine lubrication. The viscosity of the oil is the measure of this resistance to flow.

The effect of temperature on viscosity varies widely with different types of oil. The standard used to measure the amount of viscosity change with temperature is the Viscosity Index (V.I). An oil with a high viscosity index shows less change in viscosity over a wider temperature range. Refer to the Glossary of Terms, and the Additive section of this site for more information. A "multi-grade" oil has a high viscosity index.

Synthetic oils have the best low temperature flow characteristics, and are worth the extra cost in northern climates during the winter months.

2. Lubricate and Prevent Wear
The engine is now started, and the oil is being circulated by the oil pump to the engine parts. The oil must now prevent the metal-to-metal contact that will result in wear to the moving parts.

Full-film lubrication occurs when the moving surfaces are continuously separated by a film of oil. The viscosity of the oil must remain high enough to prevent metal-to-metal contact. Wear will only occur if the surface is scratched by particles thicker then the oil film. Crankshaft bearings, connecting rods, camshaft, and piston pins normally operate with full-film lubrication.

In some conditions, it is impossible to maintain a continuous oil film between the moving parts. Intermittent metal-to-metal contact occurs because of high spots on sliding surfaces, during engine starting, and in new or rebuilt engines. Lubrication under these conditions is referred to as boundary lubrication. This lubrication is accomplished by the additive package in the oil. Refer to the Glossary of Terms for further information on boundary lubrication.

3. Reduce Friction
Under full-film lubrication conditions, the film of oil prevents metal-to-metal contact. The viscosity of the oil should be high enough to maintain the film. A delicate balance must be maintained. If the viscosity is higher then required, the engine must overcome the excess fluid friction.

It is important to note that the viscosity of the oil changes as it becomes contaminated. Dirt, oxidation and sludge will increase the viscosity of the oil while fuel dilution will reduce the viscosity. This is the reason why the oil must be changed as per the schedule in the owners manual.

4. Protect Against Rust and Corrosion
Under perfect conditions, fuel burns to form carbon dioxide and water. For each gallon of fuel burned, a gallon or more of water is produced. Most of this water should escape as a vapor out of the exhaust, but some does condense on the cylinder walls. Also, water passes by the piston rings and becomes trapped in the crankcase. This is more of a problem in cold weather before the engine is warm.

In addition to water, other corrosive combustion gases also get past the rings, and are dissolved in the crankcase oil. Add to this the acids formed by the normal oxidation of oil, and the potential for rust and corrosive engine deposits become significant.

Corrosion inhibitors are part of the additive package to protect non-ferrous metals by coating them, and forming a barrier between the parts and the acids. Also, rust inhibitors are added to the oil to protect iron/steel surfaces from oxygen attack by forming a protective screen.

5. Keep Engine Parts Clean
For a variety of reasons, a gasoline or diesel engine does not burn all the fuel completely. Some of the partially burned gasoline or diesel fuel undergoes complex chemical changes during combustion, and under some conditions forms soot or carbon. Most of the partially burned fuel escapes in the form of soot through the exhaust, but part escapes past the rings into the crankcase. This combines with water to form sludge, and varnish deposits on engine parts. Sludge buildup may clog oil passages which reduces oil flow. Varnish buildup interferes with the proper clearances, restricts oil circulation, and causes vital engine parts to stick and malfunction.

Straight mineral oils have a very limited ability to keep these contaminants from forming sludge within the engine. Detergents are part of the additive package to clean-up existing deposits in the engine, as well as disperse insoluble matter into the oil. Dispersants are also part of the additive package. Both detergents and dispersants attach themselves to contaminated particles and hold them in suspension. The suspended particles are so finely divided that they can pass harmlessly between the mating surfaces, and through the oil filter. This contamination is removed when the oil is changed. Another good reason for your scheduled oil change!

6. Minimize Combustion Chamber Deposits
Some oil must reach the area of the top of the piston ring in order to lubricate the rings and the cylinder walls. It is important that the oil prevent excessive combustion deposits. Combustion deposits act as a heat barrier and as a result pistons, rings, spark plugs, and valves are not properly cooled. We all know about carbon fouled spark plugs.

The motor oil must accomplish two things in preventing excessive combustion deposits:

The oil must keep the rings free so as to reduce the amount of oil reaching the combustion chamber.
The portion of the oil reaching the combustion chamber must burn as clean as possible.

7. Cool Engine Parts
The cooling system performs about 60% of the cooling job of the engine. It cools the upper part of the engine including the cylinder heads, cylinder walls, and valves. The crankshaft, the main and connecting rod bearings, the timing gears, the pistons and other components in the lower engine are cooled as the oil flows around the parts.

What is critical is the continuous circulation of large quantities of oil. If oil passages are allowed to become clogged, the flow is restricted, and the parts are not cooled properly. Another good reason to change your oil on a regular basis, and check the oil level!

8. Seal Combustion Pressures
The surfaces of the piston rings, ring grooves, and cylinder walls are not completely smooth. This would become evident under a microscope as small hills and valleys. For this reason, the rings can never prevent high combustion and compression pressures from escaping into the low pressure area of the crankcase. This would result in a reduction of engine power and efficiency. Motor oil fills in the hills and valleys and greatly improves the seal. Because the oil film is only about 0.025 mm thick, it cannot compensate for excessive wear of the rings, ring grooves, or cylinder walls. In a new or rebuilt engine, oil consumption will be relatively high until these surfaces have been smoothed out enough to allow the oil to form a good seal.

9. Engine Oil Must be Non-Foaming
Because of the rapidly moving parts in an engine, oil is constantly being mixed with air. This produces foam which is a lot of air bubbles which may or may not readily collapse. These air bubbles normally rise to the surface and break, but water and other contaminants slow this process.

Foam is not a good conductor of heat, and will impair the cooling of the engine parts. Also, foam does not have the ability to carry much of a load which would result in excessive engine wear.

Foam depressant additives are used in the manufacture of automotive lubricants, to reduce the amount of foaming.


Detergents are used to perform two key functions. One is to neutralize the acidity byproducts of lubricant oxidation and thermal decomposition and the other is to keep contaminants as sludge of oxidized oil soluble. The total base number (TBN) of the detergent reflects its ability to neutralize acids.

Dispersants control contamination from low temperature operation. Both detergents and dispersants attach themselves to contaminant particles, and hold them in suspension. The suspended particles are so finely divided that they pass harmlessly between mating surfaces and through oil filters. The contamination is removed from the engine when the oil is changed.

Oxidation Inhibitors reduce oxygen attack on the lubricating base oil.

Corrosion Inhibitors protect non-ferrous metals by coating them and forming a barrier between parts and their environment.

Rust Inhibitors protect iron/steel from oxygen attack, by forming a protection screen over the surface of the metals.

Friction modifiers reduce friction by physical adsorption of polar materials on metal surfaces (fatty acids and esters,  molybdenum compounds...).

Anti-Wear agents form a protective layer by chemical reaction with the metal surface (normally a metal soap).

Extreme Pressure additive also known as antiseize additive, antiscuffing additive, form a protective layer by chemical reaction with the metal surface, increasing the load at which scuffing or seizure occurs.

Foam Depressants controls the tendency for fouming. Detergent and dispersant additives can facilitate aeration of an oil which results in foaming. This can reduce the lubricating ability of the oil, and interfere with the pumping of the oil.

Viscosity Index (VI) Improvers control the viscosity of multi-grade oils. They are long-chain polymers that function by uncoiling or dissociating at elevated temperatures, increasing the oil's resistance to flow. At low temperatures, they are "tight-balls" which do not significantly increase the oils resistance to flow.

Pour Point Depressants give an oil better low temperature fluidity.


reference: http://www.mts.net/~dbrad1/index.htm#Reference