Motor Oil

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Evolution of the ICE

2020 Mercedes 4-Cyl – 382 HP / 354 lb-ft Torque

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).

API

“API Donut”

The 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 / Viscocity)

SAE 5W-30 Weight

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.

Engine Oil by Engineering Explained (YouTube Playlist)

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) and diesel engines (compression ignited).

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

Spark Ignited Classes

SN Service Class

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 to be obsolete.

Table of API “S” Class Oils

ClassDateStatusComment
SP2020CurrentMatches 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.
SN2011CurrentFor 2020 and older automotive engines.
SM2010CurrentFor 2010 and older automotive engines.
SL2004CurrentFor 2004 and older automotive engines.
SJ2001CurrentFor 2001 and older automotive engines.
SH1996ObsoleteFor 1996 and older automotive engines.
SG1993ObsoleteFor 1993 and older automotive engines.
SF1988ObsoleteFor 1988 and older automotive engines.
SE1979ObsoleteFor 1979 and older automotive engines.
SD1971ObsoleteFor 1971 and older automotive engines.
SC1967ObsoleteFor 1967 and older automotive engines.
SB1951ObsoleteFor 1951 and older automotive engines.
SA1930ObsoleteFor 1930 and older automotive engines.

Compression Ignited Classes

CK-4 Service Class

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”. Any classes except those listed in the table below are considered to be obsolete.

Table of API “C” Class Oils

ClassDateComment
CK-42017API 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.
CJ-42010For 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.
CI-42002Introduced in 2002. For high-speed, four-stroke engines designed to meet 2004 exhaust emission standards implemented in 2002.
CH-41998Introduced in 1998. For high-speed, four-stroke engines designed to meet 1998 exhaust emission standards.

Table of API “F” Class Oils

In 2017 a specifically formulated oil for use in select high-speed four-stroke cycle diesel engines was designed. Since this oil is not compatible with the “C” class diesel oils, it was given a separate class of “F”

ClassYearComment
FA-42017API Service Category FA-4 describes 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.

ILSAC Standard For Passenger Car

The ILSAC standard is similar to the API class but it includes more energy conserving requirements. In some cases an oil could meet both an API and ILSAC standard as shown in the image.

Table of ILSAC Passenger Car Standards

NameStatusService
GF-6May 2020
GF-5CurrentIntroduced in October 2010, designed to provide improved high temperature deposit protection for pistons and turbochargers, more stringent sludge control, improved fuel economy, enhanced emission control system compatibility, seal compatibility, and protection of engines operating on ethanol-containing fuels up to E85.
GF-4ObsoleteUse GF-5 where GF-4 is recommended.
GF-3ObsoleteUse GF-5 where GF-3 is recommended.
GF-2ObsoleteUse GF-5 where GF-2 is recommended.
GF-1ObsoleteUse GF-5 where GF-1 is recommended.

YouTube Playlist: New Oil Standards

Lesson Resources

API Website: API “S” Class (Gasoline) Standards
API Website: API “C” Class (Diesel) Standards
API Website: API “F” Class (Diesel) Standard
API Website: ILSAC Standards For Passenger Cars
API PDF Download: 2019 Oil Guide From API / ILSAC

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