Motor Oil

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Table of Contents

Evolution of the ICE

The internal combustion engines (ICE) in today’s modern cars are truly an engineering marvel. They are smaller, lighter, more durable, and more powerful than ever before, yet they continue to meet ever-increasing emission standards. However, the most engineered and improved component that contributes to the success of today’s ICE is probably the motor oil.

Motor oil is pumped throughout the engine so every bearing rides on a film of pressurized oil, but it doesn’t stop there. All the other internal parts of the engine are bathed in oil to reduce friction, and to aid in cleaning, cooling, and sealing.

As new features are added to engines, oil keeps getting new jobs to do. Most modern engines are now equipped with variable valve timing (VVT) systems and oil pressure is used to change the cam’s timing. Also, turbochargers and superchargers that are driving the small engine / high power era are also cooled and lubricated by the engine oil.

Industry Organizations

The industry standards for motor oil are developed and established by two main agencies: The American Petroleum Institute (API) and the International Lubricant Standardization and Approval Committee (ILSAC).

American Petroleum Institute (API)

The American Petroleum Institute (API) is 100 years old (founded in 1919) and is responsible for the “API Donut” which is found on the back of virtually every oil container and shown in the image to the left. API works closely with automotive and petroleum engineers to establish standards for the viscosity and service classes of motor oil.

API also works closely with ILSAC which adds the fuel conservation component to motor oil standards.

ILSAC

ILSAC (International Lubricants Standardization and Approval Committee) was formed in 1992 by the AAMA (American Automobile Manufacturers Association) and JAMA (Japan Automobile Manufacturers Association) to work in conjunction with API to develop more stringent service classes that included fuel conservation standards.

ILSAC publishes a set of service classes (GF-1, GF-2, GF-3, GF-4, GF-5, and GF-6) that often parallel API’s service classes.

Grade (Weight / Viscosity)

Newer engines are built to tighter tolerances and operate at higher temperatures than ever before. To meet this challenge, all current oils have viscosity index improvers added that make them multigrade oils. Multigrade oils can maintain an acceptable level of viscosity over a wide temperature range.

An oil’s weight (or viscosity/grade) is the middle number in the API donut as highlighted in the illustration. The first number (5W) designates the oil’s viscosity characteristics at low temperatures and the second number (30) designates the oil’s viscosity characteristics at high temperatures The weight must match the car manufacturer’s specification or risk the chance of engine damage.

If Weight Is Too Thick – If the weight of engine oil is too thick, (a high number) it may not flow through the oil pump intake fast enough for the pump to make adequate oil pressure on cold engine starts. This could cause engine bearing damage.

If Weight is Too Thin – If the weight of engine oil is too thin, (a low number) it may flow through bearing clearances too fast during high engine temperatures and cause engine bearing damage.

API Service Class

The API service class takes into consideration almost every other property of oil except for its weight. Service classes basically fall into two categories those for gasoline engines, spark ignited (S) and diesel engines, compression ignited (C).

The service class is shown on the “API Donut”.

Spark Ignited Classes

Spark ignited (Gas) API service classes start with an “S”. The second letter started with “A” in 1930 and advanced through the alphabet as new classes are established. The current service class is “P”. Any service class lower than a “J” is considered obsolete as shown in the table below.

As detailed later in this lesson, oils designed for use in a compression ignited engine (Diesel) are “C” class oils.

Table of API “S” Class Oils

Class	Status	Comment
SP	Current	Introduced in May 2020, 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.
SN	Current	For 2020 and older automotive engines
SM	Current	For 2010 and older automotive engines.
SL	Current	For 2004 and older automotive engines.
SJ	Current	For 2001 and older automotive engines.
SH	Obsolete	CAUTION: Not suitable for use in most gasoline-powered automotive engines built after 1996. May not provide adequate protection against build-up of engine sludge, oxidation, or wear.
SG	Obsolete	CAUTION: Not suitable for use in most gasoline-powered automotive engines built after 1993. May not provide adequate protection against build-up of engine sludge, oxidation, or wear.
SF	Obsolete	CAUTION: Not suitable for use in most gasoline-powered automotive engines built after 1988. May not provide adequate protection against build-up of engine sludge.
SE	Obsolete	CAUTION: Not suitable for use in most gasoline-powered automotive engines built after 1979.
SD	Obsolete	CAUTION: Not suitable for use in most gasoline-powered automotive engines built after 1971. Use in more modern engines may cause unsatisfactory performance or equipment harm.
SC	Obsolete	CAUTION: Not suitable for use in most gasoline-powered automotive engines built after 1967. Use in more modern engines may cause unsatisfactory performance or equipment harm.
SB	Obsolete	CAUTION: Not suitable for use in most gasoline-powered automotive engines built after 1951. Use in more modern engines may cause unsatisfactory performance or equipment harm.
SA	Obsolete	CAUTION: Contains no additives. Not suitable for use in most gasoline-powered automotive engines built after 1930. Use in modern engines may cause unsatisfactory performance or equipment harm.

Compression Ignited Classes

Compression ignited (Diesel) API service classes start with an “C”. The second letter started with “A” in 1959 and advanced through the alphabet as new classes are established. The current service class is “K”.

All API “C” class oils are listed below, note that many lower class oils are now considered obsolete.

Table of API “C” Class Oils

Category	Status	Service
CK-4	Current	API Service Category CK-4 describes oils 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. These oils are formulated for use in all applications with diesel fuels ranging in sulfur content up to 500 ppm (0.05% by weight). However, the use of these oils with greater than 15 ppm (0.0015% 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	Current	For high-speed four-stroke cycle diesel engines designed to meet 2010 model year on-highway and Tier 4 non-road exhaust emission standards as well as for previous model year diesel engines. These oils are formulated for use in all applications with diesel fuels ranging in sulfur content up to 500 ppm (0.05% by weight). However, the use of these oils with greater than 15 ppm (0.0015% by weight) sulfur fuel may impact exhaust aftertreatment system durability and/or drain interval. API CJ-4 oils exceed the performance criteria of API CI-4 with CI-4 PLUS, CI-4, CH-4, CG-4 and CF-4 and can effectively lubricate engines calling for those API Service Categories. When using CJ-4 oil with higher than 15 ppm sulfur fuel, consult the engine manufacturer for service interval.
CI-4	Current	Introduced in 2002. For high-speed, four-stroke engines designed to meet 2004 exhaust emission standards implemented in 2002. CI-4 oils are formulated to sustain engine durability where exhaust gas recirculation (EGR) is used and are intended for use with diesel fuels ranging in sulfur content up to 0.5% weight. Can be used in place of CD, CE, CF-4, CG-4, and CH-4 oils. Some CI-4 oils may also qualify for the CI-4 PLUS designation.
CH-4	Current	Introduced in 1998. For high-speed, four-stroke engines designed to meet 1998 exhaust emission standards. CH-4 oils are specifically compounded for use with diesel fuels ranging in sulfur content up to 0.5% weight. Can be used in place of CD, CE, CF-4, and CG-4 oils.
CG-4	Obsolete	CAUTION: Not suitable for use in most diesel-powered automotive engines built after 2009.
CF-4	Obsolete	CAUTION: Not suitable for use in most diesel-powered automotive engines built after 2009.
CF-2	Obsolete	CAUTION: Not suitable for use in most diesel-powered automotive engines built after 2009. Two-stroke cycle engines may have different lubrication requirements than four-stroke engines, so the manufacturer should be contacted for current lubrication recommendations.
CF	Obsolete	CAUTION: Not suitable for use in most diesel-powered automotive engines built after 2009. Later “C” category oils are usually suitable or preferred for diesel automotive engines for which “CF” oils were specified. Older equipment and/or two-stroke diesel engines, especially those calling for monograde products, may however require “CF” category oil.
CE	Obsolete	CAUTION: Not suitable for use in most diesel-powered automotive engines built after 1994.
CD-II	Obsolete	CAUTION: Not suitable for use in most diesel-powered automotive engines built after 1994.
CD	Obsolete	CAUTION: Not suitable for use in most diesel-powered automotive engines built after 1994.
CC	Obsolete	CAUTION: Not suitable for use in most diesel-powered engines built after 1990.
CB	Obsolete	CAUTION: Not suitable for use in most diesel-powered engines built after 1961.
CA	Obsolete	CAUTION: Not suitable for use in most diesel-powered engines built after 1959.

ILSAC Service Class Oils

Service Class	Status	Comment
GF-6A	Current	Introduced in May 2020, designed 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.
GF-6B	Current	Applies only to oils having an SAE viscosity grade of 0W-16. Introduced in May 2020, designed to 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.
GF-5	Obsolete*	Use GF-6A where GF-5 is recommended.
GF-4	Obsolete	Use GF-5 where GF-4 is recommended.
GF-3	Obsolete	Use GF-5 where GF-3 is recommended.
GF-2	Obsolete	Use GF-5 where GF-2 is recommended.
GF-1	Obsolete	Use GF-5 where GF-1 is recommended.