Lubrication System


Oil TBN vs. Fuel Sulfur Content

Graph for determination of necessary TBN. Find the fuel sulfur percentage on bottom of the graph. Find point where the new oil TBN line intersects the sulfur content line, and read the required TBN at the left side of the chart.

Rule of Thumb: New oil TBN should be 10 times fuel sulfur content. Change oil when TBN drops to 1/2 its original value when using API CF-4 oil and you are using a DI engine.


There are chemical substances added to a petroleum product to impart or improve certain properties.

Additives strengthen or modify certain characteristics of the base oil. Ultimately, they enable the oil to meet requirements quite beyond the abilities of the base oil.

The most common additives are: detergents, oxidation inhibitors, dispersants, alkalinity agents, anti-wear agents, pour-point depressants and viscosity improvers.

Here is a brief description of what each additive does and how.

Detergents help keep the engine clean by chemically reacting with oxidation products to stop the formation and deposit of insoluble compounds.

Oxidation inhibitors help prevent increases in viscosity, the development of organic acids and the formation of carbonaceous matter.

Dispersants help prevent sludge formation by dispersing contaminants and keeping them in suspension.

Alkalinity agents help neutralize acids.

Anti-wear agents reduce friction by forming a film on metal surfaces.

A pour-point depressant keeps the oil fluid at low temperatures by preventing the growth and agglomeration (the gathering together into a mass) of wax crystals.

Viscosity improvers help prevent the oil from becoming too thin at high temperatures.

Anti-Wear Additive

This is an additive in a lubricant that reduces friction and excessive wear.

API (American Petroleum Institute)

This is a trade association of petroleum producers, refiners, marketers, and transporters, organized for the advancement of the petroleum industry by conducting research, gathering and disseminating information, and maintaining cooperation between government and the industry on all matters of mutual interest. One API technical activity has been the establishment of API Engine Service Categories for lubricating oils.

API Engine Service Categories

Gasoline and diesel engine oil performance levels are established jointly by API, SAE, and ASTM called API Engine Service Classifications. API Service Categories are as follows:

Diesel Engine Oils

Gasoline Engine Oils

Anti-Wear Additive

This is an additive in a lubricant that reduces friction and excessive wear.

Ash Content

This is the noncombustible residue of a lubricating oil or fuel. Lubricating oil detergent additives contain metallic derivatives, such as barium, calcium, and magnesium sulfonates, that are common sources of ash. Ash deposits can impair engine efficiency and power. See detergent.

ASTM (American Society for Testing and Materials)

This organization is devoted to "the promotion of knowledge of the materials of engineering and the standardization of specifications and methods of testing." A preponderance of the data used to describe, identify, or specify petroleum products is determined in accordance with ASTM test methods.

Base Stock

Base stock is a primary refined petroleum fraction, usually a lube oil, into which additives and other oils are blended to produce finished products.

Bid Oil

This is oil produced by an oil company which just meets the minimum of the diesel engine oil performance specifications. These oils are usually the least expensive because they have only the minimum amount of additives to just get by. These oils might be acceptable for lightly loaded applications but could cause problems in more severe machine application.


This comes from an internal combustion engine where seepage of fuel and gases past the piston rings and cylinder wall into the crankcase, results in crankcase oil dilution and sludge formation.


Brake mean effective pressure is the theoretical average pressure that would have to be imposed on the pistons of a frictionless engine (of the same dimensions and speed) to produce the same power output as the engine under consideration; a measure of how effectively an engine utilizes its piston displacement to do work.

Borderline Pumping Temperature °C (ASTDM D3829)

This is the temperature at which the oil becomes too viscous (thick) and cannot be moved when force is applied. The oil, however, is not yet a solid (pour point).

Bulk Delivery

This is a large quantity of unpackaged petroleum product delivered directly from a tank truck, tank car, or barge into a consumer's storage tank.


A colloid is a suspension of finely divided particles 5 to 5000 angstroms in size in a gas or liquid, that do not settle and are not easily filtered. An Angstrom is a unit of wave length of light equal to one ten billionth of a meter which carries a positive or negative charge.

Colloids are usually ionically stabilized by some form of surface charge on the particles to reduce the tendency to aggolomerate (gather into a ball or mass). A lubricating grease is a colloidal system, in which metallic soaps or other thickening agents are dispersed in, and give structure to, the liquid lubricant.

Color Scale

These scales serve primarily as indicators of product uniformity and freedom from contamination. The scale is a standardized range of colors against which the colors of petroleum products may be compared. There are a number of widely used systems of color scales, including: ASTM scale (test method ASTM D 1500), the most common scale, used extensively for industrial and process oils.

Crude Oil

Crude oil is a complex, naturally occurring fluid mixture of petroleum hydrocarbons, yellow to black in color, and also containing small amounts of oxygen, nitrogen, and sulfur derivatives and other impurities. Crude oil was formed by the action of bacteria, heat, and pressure on ancient plant and animal remains, and is usually found in layers of porous rock such as limestone or sandstone, capped by an impervious layer of shale or clay that traps the oil. Crude oil varies in appearance and hydrocarbon composition depending on the locality where it occurs. Crude is refined to yield petroleum products.

Demerit Rating

This is an arbitrary graduated numerical rating sometimes used in evaluating engine deposit levels following testing of an engine oil's detergent-dispersant characteristics. On a scale of 0-10, the higher the number, the heavier the deposits. A more commonly used method of evaluating engine cleanliness is merit rating. See Engine Deposits.


This is an important component of engine oils that helps control varnish, ring zone deposits, and rust by keeping insoluble particles in suspension and in some cases, by neutralizing acids. A detergent is usually a metallic compound. Because of its metallic composition, a detergent leaves a slight ash when the oil is burned. A detergent is normally used in conjunction with a dispersant.


A dispersant is an engine oil additive that helps prevent sludge, varnish, and other engine deposits by keeping soot particles suspended in a colloidal state (prevents these particles from gathering into a ball or mass).

Engine Deposits

These are hard or persistent accumulations of sludge, varnish, and carbonaceous residues due to blow-by of unburned and partially burned (partially oxidized) fuel, or from partial breakdown of the crankcase lubricant. Water from condensation of combustion products, carbon, residues from fuel or lubricating oil additives, dust, and metal particles also contribute. Engine deposits can impair engine performance and damage engine components by causing valve and ring sticking, clogging of the oil screen and oil passages, and excessive wear of pistons and cylinders. Hot, glowing deposits in the combustion chamber can also cause pre-ignition of the air-fuel mix. Engine deposits are increased by short trips in cold weather, high temperature operation, heavy loads (such as pulling a trailer), and over-extended oil drain intervals.

EPA (Environmental Protection Agency)

The EPA is an agency of the federal executive branch, established in 1970 to abate and control pollution through monitoring, regulation, and enforcement, and to coordinate and support environmental research.

Fighting Grade Oil

See Bid Oil.


This is the lowest temperature at which the vapor of a combustible liquid can be made to ignite momentarily in air. Flash point is an important indicator of the fire and explosion hazards associated with a petroleum product.


Lubrication is the control of friction and wear by the introduction of a friction-reducing film between moving surfaces in contact. The lubricant used may be a fluid, solid, or plastic substance.

Merit Rating

This is an arbitrary graduated numerical rating commonly used in evaluating engine deposit levels when testing the detergent-dispersant characteristics of an engine oil. On a scale of 10-0, the lower the number, the heavier the deposits. A less common method of evaluating engine cleanliness is demerit rating. See Engine Deposits.

Mineral Oil

This is any petroleum oil, as contrasted to animal or vegetable oils. Also, a highly refined petroleum distillate, or white oil, used medicinally as a laxative.

OSHA (Occupational Safety and Health Administration); Oxidation

Oxidation is the chemical combination of a substance with oxygen. All petroleum products are subject to oxidation. This degrades their composition and lowers their performance. The oxidation process is accelerated by heat, light, metal catalysts (agents which bring about a chemical reaction) and the presence of water, acids or solid contaminants.

These substances react with each other to form sludges, vanishes and gums that can impair equipment operation.

To minimize oxidation and its effects, carefully select a good base stock oil, insure an oxidation inhibitor is added to the base stock and maintain equipment and change oil to prevent contamination and excessive heat.

Oxidation Inhibitor

This is any substance added in small quantities to a petroleum product to increase its oxidation resistance, thereby lengthening its service or storage life; also called anti-oxidant. An oxidation inhibitor may work in one of three ways (1) by combining with and modifying peroxides (compounds high in oxygen) to render them harmless, (2) by decomposing the peroxides, or (3) by rendering an oxidation catalyst (metal or metal-ions) inert; that is, lacking in a chemical reaction. See Oxidation.

Oxidation Stability

This is the resistance of a petroleum product to oxidation; hence, a measure of its potential service or storage life. There are a number of ASTM tests to determine the oxidation stability of a lubricant or fuel, all of which are intended to simulate service conditions on an accelerated basis. In general, the test sample is exposed to oxygen or air at an elevated temperature, and sometimes to water or catalysts (usually iron or copper). Depending on the test, results are expressed in terms of the time required to produce a specified effect (such as pressure drop), the amount of sludge or gum produced, or the amount of oxygen consumed during a specified period.


See Bid Oil.

Pour Point

Pour point is the lowest temperature at which an oil or distillate fuel is observed to flow, when cooled under conditions prescribed by test method ASTM D97. The pour point is 3°C (5°F) above the temperature at which the oil in a test vessel shows no movement when the container is held horizontally for five seconds. Pour point is lower than wax appearance point or cloud point. It is an indicator of the ability of an oil or distillate fuel to flow at cold operating temperatures.

Ring Land

This is the area on the surface of the piston that is between either the top of the piston and first ring groove or between two adjacent ring grooves.

Ring Sticking

Ring sticking is freezing of a piston ring in its groove, in a piston engine or reciprocating compressor, due to heavy deposits in the piston ring zone. This prevents proper action of the ring and tends to increase blow-by into the crankcase and to increase oil consumption by permitting oil to flow past the ring zone into the combustion chamber. See Engine Deposits.

SAE (Society of Automotive Engineers)

The Society of Automotive Engineers reviews the total automotive engine and lubricant situation and defines the requirement for new oil specifications.

SAE Oil Viscosity Classification

Because of the important effects of oil viscosity the Society of Automotive Engineers (SAE) has developed a system for classifying lubricating oils in terms of viscosity only; no other physical or performance characteristics are considered.

The viscosity numbers without the letter W are based upon 210°F viscosities. Viscosity at that temperature correlates with oil consumption and other oil performance characteristics influenced by viscosity at normal engine operating temperatures. The viscosity numbers with the letter W are based on 0°F viscosities.

The 0°F viscosities for W-numbered oils were selected because they correlate with the cranking characteristics of motor oils in the average automobile engine under low-temperature starting conditions.

Viscosity Grades for Engine Oils

Single-Grade Oil

This is the engine oil that meets the requirements of a single SAE viscosity grade classification. i.e., SAE 10W, 30 and 40.


Scote stands for single cylinder oil test engine. Cat developed, tested and supports the single cylinder oil test engine for the CF-4 engine oil service category. This test is known as the Cat 1K Scote.

Shear Stability

Shear stability is the ability of a multiviscosity oil to resist shear forces (sudden and abrupt changes in movement) on the oil that would cause it to revert to the base oil and become too thin to provide adequate lubrication.


In diesel engines, sludge is a soft, black, mayonnaise-like emulsion of water, other combustion by-products, and oil formed during low-temperature engine operation. Sludge plugs oil lines and screens, and accelerates wear of engine parts. Sludge deposits can be controlled with a dispersant additive that keeps the sludge constituents finely suspended in the oil. See Engine Deposits.


This is unburned fuel. Black smoke and a dirty air filter indicate its presence. It causes oil to turn black.

Synthetic Lubricant

A synthetic lubricant is a lubricating fluid made by chemically reacting materials of a specific chemical composition to produce a compound with planned and predictable properties. The resulting base stock may be supplemented with additives to improve specific properties. Many synthetic lubricants - also called synlubes - are derived wholly or primarily from petrochemicals; other synlube raw materials are derived from coal and oil shale, or are lipochemicals (from animal and vegetable oils). Synthetic lubricants may be superior to petroleum oils in specific performance areas. Many exhibit higher viscosity index (V.I.) better thermal stability (heat resistance) and oxidation stability, and low volatility (which reduces oil consumption). Because synthetic lubricants are higher in cost than petroleum oils, they are used selectively where performance or safety requirements may exceed the capabilities of a conventional oil.

Total Base Number (TBN)

Understanding TBN requires some knowledge of fuel sulfur content. Most diesel fuel contains some degree of sulfur. How much depends on the amount of sulfur in the crude oil from which it was produced and/or the refiner's ability to remove it. One of the functions of lubricanting oil is to neutralize sulfur by-products, namely sulfurous and sulfuric acids and thus retard corrosive damage to the engine. Additives in the oil contain alkaline compounds which are formulated to neutralize these acids. The measure of this reserve alkalinity in an oil is known as its TBN. Generally, the higher the TBN value, the more reserve alkalinity or acid-neutralizing capacity the oil contains.


This is a science that deals with poisons and their affect and with the problems involved (as clinical, industrial or legal).


Viscosity is one of the more critical properties of oil. It refers to an oil's thickness or its resistance to flow. Viscosity is directly related to how well an oil will lubricate and protect surfaces that contact one another. Regardless of the ambient temperature or engine temperature, an oil must flow sufficiently to ensure an adequate supply to all moving parts.

The more viscous (or thicker) an oil is, the thicker the oil film it will provide. The thicker the oil film, the more resistant it will be to being wiped or rubbed from lubricated surfaces. Conversely, oil that is too thick will have excessive resistance to flow at low temperatures and so may not flow quickly enough to those parts requiring lubrication. It is therefore vital that the oil has the correct viscosity at both the highest and the lowest temperatures at which the engine is expected to operate.

Viscosity Index (VI)

Oil thins out as temperature increases. The measurement of the rate at which it thins out is called the oil's viscosity "index" (or VI). New refining techniques and the development of special additives which improve the oil's viscosity index help retard the thinning process.

The Society of Automotive Engineers (SAE) standard oil classification system categorizes oils according to their quality (via an alphabetical designation, like CD) and viscosity (via a number).


This is widely used as an anti-wear agent in motor oils to protect heavily loaded parts, particularly the valve-train mechanisms (such as the camshaft and cam followers) from excessive wear. It is also used as an anti-wear agent in hydraulic fluids and certain other products.

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