Spotlight: Understanding oil terminology

This acronym stands for the American Petroleum Institute. API is the only national trade association that represents all aspects of America’s oil and natural gas industry. Its 400 corporate members come from all segments of the industry, and are producers, refiners, suppliers, pipeline operators and marine transporters, as well as service and supply companies that support all segments of the industry, the association said.

These are chemicals that are added to the base oil that enable it to meet various performance requirements beyond the capability of the base oil. They provide wear protection, rust and corrosion protection, neutralize acids and are meant to improve the ability of the oil to disperse soot particles.

Backward Compatible
This refers to the fact that the new oil, CJ-4, can be used in older vehicles manufactured prior to 2007.

This is the nomenclature used by the API to designate the performance service categories of oil. “C” stands for commercial, “J” is the next standard letter in sequential order and 4 means that the oil is designed for use in four-stroke diesel engines.

According to Shell Lubricants, “The new category will provide improvement in several key areas which include high-temperature oxidation performance, corrosion protection, piston deposit control, soot control, valve train wear protection and improved volatility.”

Anti-wear agents, foam inhibitors, dispersants, pour point depressants, anti-rust and corrosion agents and oxidation inhibitors have been added to the new oil to provide it with new properties that will enhance the performance of the oil.

This is a condition of the oil when an unwanted substance has combined with the oil. Common contaminants include dirt, diesel fuel, soot, wear particles, water and coolant additives.

Conventional Oil
This type of oil is refined from petroleum crude oils and blended from different stocks.

This is the acronym for the diesel particulate filter, an exhaust aftertreatment device used in vehicles meeting the 2007 diesel emissions requirements. It is designed to remove particulate matter from diesel exhaust through a method of physical filtration.

This refers to destructive changes within the oil. Its causes are oxidation, nitration, loss of effectiveness and permanent viscosity changes.

This additive’s job is to help keep the engine clean. It reacts with oxidation products to stop the formation and deposit of insoluble components. Detergent additives typically are composed of metal sulfonates or salicylates to neutralize acids.

This additive disperses particulate matter and prevents soot from building up. It functions by suspending deposit-forming materials in the oil. Larger particles should be removed by the lube oil filters, and when the oil is drained, most of the remaining impurities are removed from the engine.

Fuel Dilution
Excessive fuel dilution is caused by improper operation, such as extended idling, low compression or defects in the fuel delivery system.

Oil Thinning
Fuel dilution is the most common cause of oil thinning in diesel engines. Shearing or breaking apart of the long chain molecules used in multi-viscosity oils also contributes to abnormal oil thinning. Migration of lighter hydraulic or transmission fluids can reduce the viscosity, causing abnormal thinning.

Oil Thickening
Excessive amounts of insoluble solids and fluids present in the oil are the primary contributors to increases in the viscosity. Water and water-based coolant form emulsions in the oil, restricting its ability to flow freely. High temperatures and the presence of glycol also will result in increased oil thickening.

This is the process by which oils eventually degrade because of their constant exposure to heat and air; oxidation can result in oil thickening.

This is a black, powdery form of carbon that is produced when oil is burned. The generation of soot is proportionate to operating conditions, air-to-fuel ratios and combustion/exhaust efficiency.

If it is not controlled by lubricant dispersants and removed by oil filtration, soot eventually forms into gels, creating crankcase sludge and hard carbon deposits, which can restrict oil flow, affect oil cooling, plug oil filters and increase viscosity.

Synthetic Oil
This type of oil is formed by several chemical processes in order to create materials of a specific chemical composition, then produces a compound with planned and predictable properties.

This stands for total acid number, and is the amount of potassium hydroxide in milligrams that is needed to neutralize the acids in one gram of oil.

TAN may be an important indicator of quality oil, especially when defining the oxidative status.

This stands for total base number, and is the alkalinity of the oil, which is needed to neutralize the acids that are produced in exhaust gas recirculation engines.

Generally, the higher the TBN, the more acid neutralizing capacity the oil has. A good quality oil has a TBN in the range of 10 to 13. Under CJ-4, the good quality oils will be in the range of 8.5 to 10, so there’s a decrease in the TBN of the oil.

Because of the introduction of ultra-low-sulfur diesel fuel to the industry, TBN levels may not be as important as they were in the past.

This is the acronym for ultra-low-sulfur diesel fuel, which will be required for all diesel engines built for use in on-highway trucks beginning with model year 2007 to meet the new emissions requirements. It is necessary for advanced emission control devices like oxidation catalysts and particulate filters to function properly.

Used Oil Analysis
Used oil analysis can be defined as a preventive maintenance tool which can be used to detect contaminants, determine the overall condition of the lubricants and assist in monitoring component wear conditions.

VM is the acronym for viscosity modifiers. Multi-grade engine oils contain oil-soluble organic polymers, referred to as viscosity modifiers, which provide a thickening effect at higher temperatures.

Viscosity Grade
This is the measure of an oil’s thickness and ability to flow at certain temperatures. Vehicle requirements may vary, so you should follow the vehicle manufacturer’s recommendations on SAE oil viscosity grade.

Editor’s Note: Truck Parts & Service wishes to thank the Technology & Maintenance Council for information used in this article.

A Simple Checklist
The American Petroleum Institute (API) offered the following guidelines to help you get more from your engine oil.

  • Refer to the owner’s manual for the appropriate type of oil to use in your customer’s vehicle.
  • Be sure to follow the manufacturer’s oil change recommendations and procedures.
  • Use only the recommended API category: “S” for gasoline engines; “C” for diesel engines.
  • Select the proper SAE oil viscosity grade for the vehicle’s particular application.
  • If you find it necessary to mix brands of oil in the vehicle, use the same viscosity grade and API service category to maintain performance.
  • Properly dispose of used oil.

For More Information
For more information on oil, you may contact the following companies directly, or use the FREE Reader Service Card in this issue. Other companies offering information on oil can be found in the Truck Parts & Service Aftermarket Buyers’ Guide & Directory as well as in Buyers’ Guide section on our web site at

BP Lubricants America
Baltimore, MD

Castrol Heavy Duty Lubricants Inc.
Baltimore, MD

Chevron Products Corp.
San Ramon, CA

CITGO Petroleum Corporation
Tulsa, OK

Houston, TX

ExxonMobil Corp.
Fairfax, VA

Kendall Motor Oil
Houston, TX

Champion Laboratories Inc.
Albion, IL

Petro-Canada America
Lubricants Inc.
Chicago, IL

Shell Lubricants
Houston, TX

The Valvoline Company
Ashland Laboratory
Lexington, KY

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