New Classification System For Automotive Engine Oils

New Classification System For Automotive Engine Oils

Apparatus Maintenance

In this age of technical achievement and change, the problems and procedures for proper fire apparatus maintenance are changing too. The adoption of the diesel engine and the automatic transmission are two examples of change that brought a need for knowledge and understanding of construction, operation and maintenance requirements to provide effective and reliable service.

Now, there are two more subjects vital to maintenance that are changing. These are engine lubricating oil classification and brake systems. First, a review of the classification system with an explanation of the reasons for change.

The first engine oil classification system was adopted by the Society of Automotive Engineers (SAE) in 1911. This system, still in use, is based on the viscosity of the oil and no change is contemplated in this form of classification. A description of the viscosity rating classification, in detail, is given on page 22 of “Preventive Apparatus Maintenance,” published by Fire Engineering.

The SAE viscosity classification system worked very well for the early automotive engines, which were usually of the relatively slow speed type, about 3000 rpm maximum, and with ample cooling. There were no high speed expressways and no pressurized cooling systems to permit higher temperature operation.

Change in refining: During World War II, changes were made in the refining process of crude oil that permitted a greater production of lubricants and fuels from a gallon of crude. In this solvent process of refining, oil lost some of its required properties, so additives to provide these lost properties became a part of the oil formulation. Changes in engine design were being made to produce more power and to operate at higher rpm, contributing to the problem for adequate lubrication.

To provide a system that would permit classification for types of use, the American Petroleum Institute (API) adopted in 1947 a designation for three types: regular type, premium type and heavy-duty type. The regular type oils were straight mineral oils. The premium type oils contained additives for reducing friction (oiliness) and oxidation inhibitors. Heavy-duty type oils contained the friction reducing additive, anti-oxidant inhibitor and detergent-dispersant additives.

After several years usage of these classifications, the engine and oil manufacturers recognized that this system did not allow for the differences in engine operating characteristics, conditions of operation or types of fuel used in gasoline and diesel engines. To provide a better classification system that would satisfy these differences and better meet operating conditions, a new system of classification was developed by the API and the American Society for Testing and Materials (ASTM) in 1952. The system was revised in 1955 and again revised in 1960.

The 1960 revision is the current classification, which is ML, MM and MS for gasoline engines and DG, DM and DS for diesel engines.

More flexibility needed: This system has been an improvement over the previous system, but after about 10 years of usage it became apparent there was a need for a more flexible system. Because the internal combustion engine is now used in such a wide variety of services under greatly varying conditions of load, long idling or full load, high temperature (ambient), low temperature, sustained speed at high rpm and high load without warmup (emergency), a more effective system is needed to permit classification communication that is relevant among the engine manufacturer, the petroleum industry and the user.

To study this need and develop a better classification system, in 1969 and 1970 the API, ASTM and SAE cooperated to establish a new system. The SAE determined there were eight categories of automotive type engine oils that were of current commercial application. ASTM established the test methods, performance characteristics and technically described each of the categories. API prepared a user language, including new engine service letter designations for each of the eight different operating conditions for each type of oil.

This new classification system is SAE Recommended Practice J-183.

It is to be hoped that the tests required for each class of oil in the new system are sufficiently thorough to eliminate some of the poor quality oils that have been, and still are, marketed by refiners. As refiners test and classify their own oil, a wide margin of oil stability and performance exists between brands having the same classification marking.

Additives consumed: During the past year, the number of cases reported of engine oil thickening to become a gelatin has greatly increased. There are limits to what an engine oil can do, and additives not only have a limit too, but they are consumed during engine operation and can only be replaced safely by draining and refilling with fresh oil. So, maintenance with oil filter changes at least every other drain will still be required. If heavy sludge is found on the filter at the time of change, it indicates the detergent additive in the oil is exhausted. A new filter should be installed and the oil change interval should be shortened. Three months is the recommended maximum for an emergency fire service oil change schedule.

The new API classification is an open-ended system which permits new categories to be added as required without changing or deleting existing categories.

The new system continues the use of letter designations for each service classification. The letters provide a convenient means for the engine manufacturer to indicate the service characteristics for the engine, hence the lubrication requirement. Petroleum refiners use the letter designation to indicate the class or classes of service for which each of their brands of engine lubricating oil is suitable.

New API identifications: The new API letter designations identifying the eight service classifications are shown in the following chart:

The letter “S” is for service station general use and distribution.

SA is an oil without inhibitors, and as such has no place in fire service maintenance. No performance requirements for this oil.

SB is for minimum-duty gasoline engine service. Not recommended for fire service apparatus.

SC is a detergent-dispersant type oil with additives for anti-corrosion, antifoaming, viscosity improver and antioxident. Recommended for fire service use, gasoline engines.

Continued on page 60

Apparatus Maintenance

Continued, from page 52

SD is an improved formulation of additives over SC. it also is recommended for fire service use. It provides better protection in gasoline engines from high-temperature and low-temperature engine deposits, wear, rust and corrosion.

The letter “C” is for commercial usage.

CA is for light-duty diesel engines, but is not to be used in fire apparatus diesel engines.

CB is for use with light to moderateduty diesel engines. This classification is approved by Ford and Detroit Diesel for use in engines of their manufacture.

CC is for normally aspirated or turbo-charged diesel engines. This classification is approved by Mack and Cummins. Approval by Cummins is only for normally aspirated engines.

CD is for severe duty diesel engine service. This oil is approved by Cummins for its supercharged or turbo-charged engines.

This new system of engine oil classification became effective last January. It will be midsummer or later before it appears on containers in service stations and distributors as the inventory with the current classification marking will be used first.

Technical data was supplied through the courtesy of The American Petroleum Institute.

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