Automotive Lubricants Part I - Oil
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Oil Classifications (Let's Clear Up The Misunderstandings)

The American Petroleum Institute (API) has established a classification system for the designation of gasoline and diesel engine oils that reflects the quality, performance and suitability of the oils for various engines. These classifications, or categories, have no bearing on oil viscosity, whose limits are set by the Society of Automotive Engineers (SAE). Contrary to popular belief, the SAE grade only defines oil viscosity and has absolutely nothing to do with oil quality. Under federal law both the API service designation and the SAE viscosity grade are required.

In the United States, API also administers the licensing and certification of engine oils through a classification system that reflects the warranty, maintenance and lubrication requirements of the automotive industry. Through this system, API has standardized the labeling of engine oils by adopting the "donut" logo, which tells the user the oil's viscosity grade, engine service classification and any energy conserving capabilities.

Note: Engine oil performance requirements, test methods and limits for the various classifications are established by the engine and vehicle manufacturers and technical societies.

These classifications are arranged into two different groups, one for automotive gasoline engine service and the other for commercial diesel engine service. All gasoline engine oils use the classification "S," or "Service," presently SA through SL, as follows. Note that categories SA through SG are now obsolete, meaning any oil now available will more than meet the requirements of older engines.

SA - SB: SA and SB denotes service typical of older engines operated under such mild conditions that the protection afforded by compounded oils is not required. Oils designed for this service have been used since the 1930s and provide only mild anti-scuff capability and resistance to oxidation and bearing corrosion. They should not be used in any engines unless specifically recommended by the engine manufacturer.

SC - Category SC denotes service typical of gasoline engines in 1964 through 1967 models of passenger cars and some trucks, operating under engine manufacturers' warranties in effect during those model years. Oils designed for this service provide control of high and low temperature deposits, wear, rust and corrosion in gasoline engines.

SD - Category SD denotes service typical of gasoline engines in 1968 through 1970 models of passenger cars and some trucks, operating under engine manufacturers' warranties in effect during those model years. This category may also apply to certain 1971 or later models as specified or recommended in the owners' manuals. Oils designed for this service provide more protection against high and low-temperature deposits, wear, rust and corrosion in gasoline engines than oils that are satisfactory for API Service Category SC and may be used when API Engine Service Category SC is recommended.

SE - Category SE denotes service typical of gasoline engines in passenger cars and some trucks beginning 1972 and certain 1971 through 1979 models operating under engine manufacturers' warranties. Oils designed for this service provide more protection against oil oxidation, high-temperature engine deposits, rust and corrosion in gasoline engines than oils that are satisfactory for API Engine Categories SD or SC and may be used when either of these categories is recommended.

SF - Category SF denotes service typical of gasoline engines in passenger cars and some trucks beginning with 1980 through 1989 models operating under engine manufacturers' recommended maintenance procedures. Oils developed for this service provide increased oxidation stability and improved anti-wear performance relative to oils that meet the minimum requirements of API Service Category SE. These oils also provide protection against engine deposits, rust and corrosion. Oils meeting API Service Category SF may be used when API Engine Service Categories SE, SD, or SC are recommended.

SG - Category SG denotes service typical of gasoline engines in passenger cars, vans and light trucks beginning with 1989 through 1993 models operating under manufacturers' recommended maintenance procedures. Category SG oils include the performance properties of API Service Category CC as certain manufacturers of gasoline engines require oils that also meet the diesel engine oil category CD. Oils developed for this service provide improved control of engine deposits, oil oxidation, and engine wear relative to oils developed for previous categories. These oils also provide protection against rust and corrosion. Oils meeting API Service Category SG may be used when API Engine Service Categories SF, SE, SF/CC, or SE/CC are recommended.

SH - Category SH, first introduced in 1993, is for use in service typical of gasoline engines in present and earlier passenger cars, vans and light trucks operating under vehicle manufacturers' recommended maintenance procedures. Engine oils developed for this category provide performance exceeding the minimum requirements of API Service Category SG, which it is intended to replace, in the areas of deposit control, oil oxidation, wear, rust, and corrosion. Oils meeting API SH requirements have been tested according to the Chemical Manufacturers Association (CMA) Product Approval Code of Practice and may utilize the API Base Oil Interchange and Viscosity Grade Engine Testing Guidelines. They may be used where API Service Category SG and earlier categories are recommended. This service category was valid until August 1, 1997.

SJ - Category SJ was adopted for use in describing engine oils available in 1996. These oils are for use in service typical of gasoline engines in current and earlier passenger car, sport utility vehicle, van, and light truck operations under vehicle manufacturers' recommended maintenance procedures. Engine oils that meet the API Service Category SJ may be used where API Service Category SH and earlier Categories have been recommended.

SL - Category SL was adopted for use in describing engine oils available after July 1, 2001. Engine oils that meet the API Service Category SL may be used where API Category SJ and earlier categories have been recommended.

Conclusion

Don't make the mistake of "second-guessing" the engineers who designed your engine by using higher or lower viscosity oils than specified, since doing so makes it difficult for the pump to provide a sufficient film between bearings. In the former case there will be insufficient oil distribution and in the latter case the parts will pound out the thinner film and damage themselves.

The most important thing we can say about lubrication is this. Trust the engineers who designed your engine to have chosen the correct type and viscosity of oil for its operation.