All about oil
Oil classification and testing
Back around the turn of the century, the automotive and petroleum industries realized there had to be some method of classifying and describing crankcase oils. Between the years 1911 and 1970, constant improvements were made on the first rough attempts to classify motor oils. Today oils are classified via a system developed jointly by the American Petroleum Institute (API), the American Society for Testing and Materials (ASTM), and the Society of Automotive Engineers (SAE).
Meanwhile, the SAE was developing a separate method for measuring oil viscosity. With these two classifications, a motorist can get a better idea what he or she is getting into when buying a motor oil.
| Rating | Description |
|---|---|
| SA: | A utility grade gasoline engine oil without additives except that it may contain pour and/or foam depressants. There are no performance requirements for this grade. |
| SB: | A minimum duty gasoline engine oil with all the qualities of the SA grade, but with some anti-oxidant and anti-scuff abilities. |
| SC: | This oil was designed to meet the warranty specifications for gasoline engines from 1964 to 1967, and includes all the qualities of the SB grade, with additional additives for anti-rust and detergent/dispersant abilities. |
| SD: | Designed to meet the warranty requirements of autos manufactured from 1968 through 1970, this oil has all the qualities of SC grade oil with better anti-sludge and anti-rust additives. It may be used where API classification SC is recommended. |
| SE: | A further upgraded classification providing warranty maintenance for 1972 through 1980 passenger vehicles. In addition to better anti-sludge and anti-rust additives, it contains improved anti-oxidant additives. |
| SF: | This classification brought on by harsher engine environments, SF grade oil is designed to operate within warranty requirements in the new, hotter-running engines. |
| SG: | This rating provides improvements over the SF rating in that the oil has better oil oxidation stability, better anti-sludging, and better anti-wear. This has been done to meet warranty specifications for the 1989 cars. |
| SH: | Meets 1994 warranty requirements. All previous service categories are obsolete as of this classification. API Service Category SH was adopted in 1992 for use in describing engine oils available in 1993. These oils are for use in service typical of gasoline engines in passenger cars, vans, and light-duty trucks operating under vehicle manufacturers' recommended maintenance procedures. Engine oils developed for this Service Category provide performance exceeding the minimum requirements for API Service Category SG, which Service Category SH was intended to replace, in the areas of controlling deposits, oil oxidation, wear, rust, and corrosion. |
| SJ: | Meets 1997 warranty requirements. API Service 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 passenger cars, sport utility vehicles, vans, and light-duty trucks operating under vehicle manufacturers' recommended maintenance procedures. Engine oils that meet the API Service Category SJ designation (see Appendix G) may be used where API Service Category SH and earlier Categories have been recommended. |
| SL: | Meets 2001 warranty requirements. API Service Category SL was adopted for use in describing engine oils available in 2001. These oils are for use in service typical of gasoline engines in current and earlier passenger cars, sport utility vehicles, vans, and light-duty trucks operating under vehicle manufacturers' recommended maintenance procedures. Engine oils that meet the API Service Category SL designation (see Appendix G) may be used where API Service Category SJ and earlier S Categories have been recommended. |
| SM: | Meets 2005 warranty requirements. API Service Category SM was adopted for use in describing engine oils available in 2004. These oils are for use in service typical of gasoline engines in current and earlier passenger cars, sport utility vehicles, vans, and light-duty trucks operating under vehicle manufacturers' recommended maintenance procedures. Engine oils that meet the API Service Category SM designation (see Appendix G) may be used where API Service Category SL and earlier S Categories have been recommended. |
The S letter service classifications designate that the oil is meant for use in passenger cars. There is a C letter classification (CA, CB, CC, and CD) that refers to oils meant for commercial applications, with CD being the most stringent classification.
SAE Viscosity Ratings
Viscosity is a property of a fluid that causes it to resist flow. It is a natural tendency all oils to thicken at low temperatures and thin out at higher temperatures. This being the case, it is desirable to measure the degree of thinning and thickening and give it a number. This number is the SAE Viscosity Rating.
Base stocks can be classified in any of eight viscosities ranging from SAE 5W (low) to SAE 50 (high) The W after the number, as in SAE 5W, SAE 10W, SAE 15W, and SAE 20W, means the oil is rated for flow at 0 degrees F (for winter use). Without the W, as in SAE 20, SAE 30, SAE 40, and SAE 50, the ratings are measured at 210 degrees F. Multi-viscosity oils, which are denoted by SAE ratings such as SAE 20W50, have been compounded to act like a 20W oil at 0 degrees F and like a 50 weight oil at 210 degrees F.