The service rating of motor oils is classified by the American Petroleum Institute (API). The program certifies that an oil meets certain OEM quality and performance standards. The service rating is shown in the API "Service Symbol Donut" on the product label. There may also be an "API Certified for Gasoline Engines" seal on the label.
The latest service category rating for gasoline engines is SP. Introduced in May 2020, motor oils that meet the SP rating are designed to provide protection against low-speed pre-ignition (LSPI), timing chain wear protection, improved high temperature deposit protection for pistons and turbochargers, and more stringent sludge and varnish control. API SP with Resource Conserving matches ILSAC GF-6A by combining API SP performance with improved fuel economy, emission control system protection and protection of engines operating on ethanol-containing fuels up to E85.
The previous API Service rating was SN for 2011 to 2020 model year vehicles (except 2020 models that require SP rated oils). This rating replaced the previous SM rating that was introduced in November 2004 for 2005 and newer engines. SN-rated oils along with the previous SM, SL and SJ ratings, are all backwards compatible and can be safely used in older engines. But the opposite is not true. Older obsolete service classifications (SH, SG, SF, etc.) may not meet OEM lubrication requirements for newer engines. Likewise, API SL oils should not be used in 2005 and later vehicles, and SJ oils should not be used in 2001 and newer vehicles.
An important point to note with the new SP rated oils is that they are usually required for late model engines that has Gasoline Direct Injection (GDI), and engines with dual injection systems (GDI and Port Injection). SP oils have a revised oil chemistry that reduces the formation of intake valve deposits in GDI engines. If and oil that does not meet the SP requirements is used in an engine with GDI, over time it can result in a buildup of carbon deposits on the intake valves. This can cause rough running, and a loss of fuel economy and performance. The fix is to clean the intake valves with a chemical fuel/intake additive, or in some cases to remove the intake manifold and clean the intake valves with a chemical solvent or a bead shot blaster (using baking soda or soft media such as walnut shells), then changing the oil and using the correct SP-rated motor oil from then on.
API also gives oils an "Energy Conserving" rating if the oil meets certain criteria for reducing friction and oil consumption, and improving fuel economy. Most 5W-20 and 5W-30 oils meet this classification.
Click here for information about API Motor Oil Specifications for 2020.
For diesel engines, API has a separate rating system that include a number of oil ratings.
API Service Category CK-4 is for use in high-speed four-stroke cycle diesel engines designed to meet 2017 model year on-highway and Tier 4 non-road exhaust emission standards as well as for previous model year diesel engines (it is backwards compatible). These oils are formulated for use in all applications with diesel fuels ranging in sulfur content up to 500 ppm (0.05 percent by weight). However, the use of these oils with greater than 15 ppm (0.0015 percent by weight) sulfur fuel may impact exhaust aftertreatment system durability and/or oil drain interval. These oils are especially effective at sustaining emission control system durability where particulate filters and other advanced aftertreatment systems are used.
API CK-4 oils are designed to provide enhanced protection against oil oxidation, viscosity loss due to shear, and oil aeration as well as protection against catalyst poisoning, particulate filter blocking, engine wear, piston deposits, degradation of low- and high-temperature properties, and soot-related viscosity increase. API CK-4 oils exceed the performance criteria of API CJ-4, CI-4 with CI-4 PLUS, CI-4, and CH-4 and can effectively lubricate engines calling for those API Service Categories. When using CK-4 oil with higher than 15 ppm sulfur fuel, consult the engine manufacturer for service interval recommendations.
CJ-4 rated oils are for 2007 to 2017 diesel engines. The previous CI-4 rating was introduced back in 2002 for diesels that have exhaust gas recirculation) and can be used in 2002 to 2006 diesel engines. The previous CH-4 (introduced in 1998) can be used in 2002 and older diesels. Previous API classifications CG-4 (1995) and CF-4 (1990) are now considered obsolete. CF-2 (1994) is the API classification for two-stroke diesels.
FA-4 is a special diesel oil classification for certain XW-30 oils specifically formulated for use in select high-speed four-stroke cycle diesel engines designed to meet 2017 model year on-highway greenhouse gas (GHG) emission standards. These oils are formulated for use in on-highway applications with diesel fuel sulfur content up to 15 ppm (0.0015 percent by weight). Refer to individual engine manufacturer recommendations regarding compatibility with API FA-4 oils. These oils are blended to a high temperature high shear (HTHS) viscosity range of 2.9cP–3.2cP to assist in reducing GHG emissions. These oils are especially effective at sustaining emission control system durability where particulate filters and other advanced aftertreatment systems are used. API FA-4 oils are designed to provide enhanced protection against oil oxidation, viscosity loss due to shear, and oil aeration as well as protection against catalyst poisoning, particulate filter blocking, engine wear, piston deposits, degradation of low- and high-temperature properties, and soot-related viscosity increase.
CAUTION: API FA-4 oils are NOT interchangeable or backward compatible with API CK-4, CJ-4, CI-4 with CI-4 PLUS, CI-4, and CH-4 oils. Refer to engine manufacturer recommendations to determine if API FA-4 oils are suitable for use. API FA-4 oils are not recommended for use with fuels having greater than 15 ppm sulfur. For fuels with sulfur content greater than 15 ppm, refer to engine manufacturer recommendations.
The International Lubricant Standardization and Approval Committee (ILSAC) is similar to API except that it establishes ratings for motor oils in European and Asian vehicle applications.
GF-6A oils were introduced in May 2020 to provide protection against low-speed pre-ignition (LSPI), timing chain wear protection, improved high temperature deposit protection for pistons and turbochargers, more stringent sludge and varnish control, improved fuel economy, enhanced emission control system protection and protection of engines operating on ethanol-containing fuels up to E85. The GF-6A rating is similar to the API SP rating.
GF-6B are a special class of low viscosity oils with an SAE viscosity grade of 0W-16. Introduced in May 2020, GF-6B oils provide protection against low-speed pre-ignition (LSPI), timing chain wear protection, high temperature deposit protection for pistons and turbochargers, stringent sludge and varnish control, improved fuel economy, emission control system protection and protection of engines operating on ethanol-containing fuels up to E85.
In October 2010, the ILSAC introduced the GF-5 rating that provided better oil life, fewer deposits, less sludge and improved protection for turbochargers and the catalytic converter.
In 2011, General Motors announced a new oil requirement called dexos. GM said their dexos specification was better than the GF-5 specification at that time. GM says dexos is required in all 2011 and newer GM engines, and is backwards compatible with older engines that use SM and SN oils.
There are two versions of dexos: dexos1 for gasoline engines and dexos2 for diesel engines. The specification calls for a high quality synthetic base stock with additives that provide high temperature, high sheer characteristics to reduce friction for better fuel economy, to reduce piston ring deposits and sludge, and to extend oil life (necessary for use with GM's Oil Life Reminder System).
Because it uses high quality synthetic base stocks, dexos and other brands of oil that meet GM's dexos specification are more expensive than conventional motor oils. GM is licensing oil brands that meet their specifications.
Click here for information about the Motor Oil Specifications for 2014.
In recent years, there has been a growing problem of quick lube shops selling motorists poor quality oil. The American Petroleum Institute (API) did a nationwide survey in 2013 to check the quality of oil being sold by quick lube facilities. Oil samples were taken from bulk dispensers in quick lube shops and analyzed in a laboratory to see if they meet API quality standards, OEM performance requirements and SAE viscosity grades. The survey found that 1 out of 5 samples FAILED one or more of these tests! In other words, a lot of quick lube shops are selling poor quality oil that does not meet minimum service specifications or is not the correct viscosity grade. For more information on this issue, see Motor Oil Matters.
If you are driving an older classic muscle car or hot rod that has an engine with a flat tappet camshaft, you should be aware of the fact that today's SM, SN and SP rated motor oils contain much lower levels of anti-scuff additive called "ZDDP" (Zinc Dialkyl Dithio Phosphate). The level of ZDDP in current motor oils has been reduced to no more than 0.08% phosphorus to extend the life of the catalytic converter. Phosphorus can contaminate the catalyst over time if the engine uses oil, causing an increase in tailpipe emissions.
The lower ZDDP content is not harmful to late model engines with roller lifters or followers because the loads are much lower on the camshaft lobes. But on pushrod engines with flat tappet cams, the level of ZDDP may be inadequate to prevent cam lobe and lifter wear. In some cases, cam failures have occurred in as little as a few thousand miles of driving! This is even more of a risk in engines if stiffer valve springs and/or higher lift rocker arms are used.
To avoid such problems, you should add a ZDDP additive to the crankcase, or use an oil that meets the previous SL service rating, or use diesel motor oil or racing oil that contains adequate levels of ZDDP to protect the camshaft and lifters.
If you are installing a new camshaft in the engine, be sure to use the cam manufacturers assembly lube and follow the recommended break-in procedure. But you will still need to add ZDDP to the crankcase or use an oil that contains adequate levels of ZDDP for continued protection.