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Tom Kool

Tom Kool

Tom majored in International Business at Amsterdam’s Higher School of Economics, he is Oilprice.com's Head of Operations

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The Complete Guide To Motor Oils

Car tower

Although sales of electric vehicles (EVs) are continuing to grow around the world and are expected to keep rising in many markets, including in the United States, the overwhelming majority of the global car fleet consists of—and will continue to consist of—vehicles with internal combustion engines (ICEs).

Gasoline and diesel-powered vehicles require routine maintenance as well as fuel and motor oil to keep the engine running, to keep it running smoothly, and improve fuel economy.

Motor oils can vary in type, viscosity, function, and source materials—the way in which they were made. They have common functions in all gasoline and/or diesel-powered vehicles, but the different specifications of the various types of motor oils make them suitable for one or another type of vehicle. Car owners can’t just grab any kind of motor oil off the shelf at a service center and pour it into their vehicles. That’s because some vehicles are designed for one type of motor oil, while others drive best with another type of motor oil.

Vehicle manufacturers have specific recommendations for what type of oil must be used, the desired performance level of the oil, and how often motorists should have their motor oil changed.

These recommendations are not to be disregarded, because choosing the right motor oil can enhance the vehicle’s performance and fuel economy.

In addition, there are industry-level standards for performance requirements set by the American Petroleum Institute (API) for quality motor oils capable of best protecting drivers’ vehicles.

Bad motor oil can damage a vehicle’s engine and its performance.

The API has a certification mark and a service symbol on quality motor oils as identified by the U.S. and international vehicle engine makers and the lubricant production industry. This is a voluntary global program backed by a marketplace sampling and testing program. Related: OPEC+ Considers 500,000 Bpd Cut In Emergency Meeting

Before delving into the specifics of motor oils and which motor oils are suitable for which types of engines, let’s take a look at the

The Importance of Motor Oils in Internal Combustion Engine Vehicles

Motor oil is an indispensable part of the maintenance of a vehicle with an internal combustion engine.

So what do motor oils do?

  • Motor oil keeps the parts of the engine lubricated so the moving parts do not grind against each other, which can cause damage. Motor oil thus reduces internal mechanical friction.
  • Motor oil keeps the moving parts of the engine cool because it disperses heat.
  • Motor oil also keeps the surfaces in the engine clean.
  • Motor oil prevents corrosion and rust.
  • Motor oil helps internal combustion engines start easily. 
  • Motor oil protects the emission system.
  • Motor oil helps to enhance fuel economy. 

Types of Motor Oil

Depending on the way motor oils are made, there are three major types of motor oil:

  • Full synthetic motor oil, which consists of artificially made chemical compounds, created by breaking down and then rebuilding petroleum molecules
  • Synthetic blend motor oil, and
  • Conventional motor oil, or mineral motor oil, 75 percent to 80 percent of which is made from refined crude oil

There are differences in the performance and quality of the synthetic and conventional motor oils. As a rule of thumb, however, it is always recommended to follow the instructions and recommendations of the vehicle engine manufacturer as to what type or brand of motor oil—synthetic or conventional—to use in order to make the most of the car’s engine performance.

Conventional, or mineral motor oils, come from refining crude oil during a process that removes contaminants and unwanted hydrocarbon molecules from the crude oil. These were the first motor oils that the lubricant industry has developed for automobiles, so they are designed for use in less advanced or older motor vehicles. Conventional motor oil typically has lower performance than the newer developed synthetic motor oils. Still, manufacturers typically recommend the use of conventional motor oils in vintage and classic cars.

Synthetic motor oils have far fewer impurities compared to conventional or mineral oils, and typically feature a lot of additives to enhance lubrication and protection, including against oxidation, corrosion, and wear. For more technologically advanced engines and engine parts, synthetic oils are usually recommended.

But even among full synthetic oils, not all synthetics are the same. Each brand of full synthetic oil on the market has different mix of fluids and additives, enhancing one or another protection of the engine, at the expense of some other performance indicator.

Therefore, drivers should consider not only the recommendations of the engine manufacturer but also the typical driving conditions of their vehicles, such as:

  • Weather conditions – is the vehicle driven often in extreme cold and/or heat?
  • Is the vehicle pulling heavy loads such as a trailer or camper?
  • Is the vehicle typically driven in city conditions with lots of stops and starts?

After taking the manufacturer’s recommendations and the driving conditions into account, motorists can ask their mechanic or choose the type and brand of motor oil that best serves the performance needs of their vehicle. Using an non-specified oil in your car engine may damage your engine and could void your manufacturer’s warranty.

Choosing the right type of motor oil also protects the car’s engine and enhances its performance while preventing damage from friction and severe weather conditions.

It is recommended that motorists use quality motor oils to avoid damage to their car and have the engine operate as smoothly and efficiently as intended by the manufacturer. 

API Quality Motor Oil Marks

The API, for example, has certification marks on the motor oils that meet requirements of voluntary programs—global and national—for quality engine oils. Related: What Happens If The Next U.S. President Bans Oil Exports?

The API also has an information campaigns, Motor Oil Matters (MOM) and Diesel Oil Matters, as well as a certification mark and a service symbol to identify quality motor oils for gasoline and diesel-driven vehicles.

API-licensed motor oils display one or both of the API motor oil quality marks—the API Service Symbol “Donut” and the Certification Mark “Starburst.”  

The two marks of API-approved quality motor oils are part of the API’s Engine Oil Licensing and Certification System (EOLCS). This system is a voluntary licensing and certification program that authorizes engine oil marketers that meet specified requirements to use the API quality motor oil marks.

API’s Engine Oil Program was launched in 1993. It is a joint cooperative effort between the oil and additive industries and vehicle and engine manufacturers Ford, General Motors, and Fiat Chrysler and those represented by the Japan Automobile Manufacturers Association and the Truck and Engine Manufacturers Association. The Engine Oil Program runs regular physical, chemical, and performance tests on licensed engine oils and verifies that the API-registered Marks are properly displayed on containers and convey accurate information to consumers.

The performance requirements and test methods are established by vehicle and engine manufacturers and technical societies and trade associations such as ASTM, SAE, and the American Chemistry Council (ACC).

API’s Certification Mark, known as the “Starburst” mark, displayed on a motor oil container, means that the motor oil meets the current engine protection standard and fuel economy requirements of the International Lubricant Specification Advisory Committee (ILSAC).

The ‘Starburst’ mark, source: API

The standards under ILSAC are developed by vehicle and engine manufacturers, oil and additive companies and industry trade associations such as API, ACC, ASTM, and SAE. These oils provide engine protection while also delivering improved fuel economy and emission system protection.

The current ILSAC standard is GF-5, which was introduced in October 2010. This standard was designed to provide more protection from deposit for pistons and turbochargers in high temperatures, 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.

The API Service Symbol “Donut” 


The ‘Donut’ Service Symbol, Source: API

The API ‘Donut’ service symbol is displayed on the containers of motor oils which meet current API engine oil standards. The symbol includes the SAE viscosity grade of the oil, API standards met by the oil, and other important performance parameters.

The top of the ‘Donut’ symbol shows the motor oil’s API performance standard. The letter "S" followed by another letter (API SN) refers to oil suitable for gasoline engines in passenger cars, vans, and light trucks, where ‘S’ is for the (Service) categories. The letter "C" followed by another letter and a number (for example, API CJ-4) refers to oil suitable for diesel engines and for heavy duty trucks, under API’s C or ‘Commercial’ categories. 

The current API standards for gasoline engines are SN, SM, SL, and SJ.

SJ is for 2001 and older automotive engines running on gasoline, SL is for 2004 and older automotive engines, and SM is for 2010 and older automotive engines. The SN standard was introduced in October 2010 and is designed to provide improved high-temperature deposit protection for pistons, more stringent sludge control, and seal compatibility. API SN with Resource Conserving matches ILSAC GF-5 by combining API SN performance with improved fuel economy, turbocharger protection, emission control system compatibility, and protection of engines operating on ethanol-containing fuels up to E85.

The current API standards for Diesel C Categories are CH-4 from 1998, CI-4 from 2002, CJ-4 from 2010, and CK-4 category 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.

The center of the ‘Donut’ symbol displays the viscosity grade of the motor oil under a scale developed by the Society of Automotive Engineers (SAE). Viscosity grade is the measure of the ability of a motor oil to flow at certain temperatures. Oil grades, for example, 10W-30, are used to denote the viscosities of the oil in the winter and in the summer. The number preceding the ‘W’ is for the winter and the number after the ‘W’ is for the summer. Drivers should follow their vehicle manufacturer’s recommendations on oil viscosity as graded by SAE.

A 0W-30 rated oil will perform better in extremely cold temperatures than a 10W-30 oil, for example.

The bottom of API’s “Donut” symbol displays whether the motor oil has resource-conserving properties when compared with a reference motor oil in an engine test. Motor oils labeled as ‘Resource Conserving’ have passed this test. Widespread use of motor oils with the “Resource Conserving” mark may lead to overall savings of fuel in the total vehicle fleet, according to the API.     

The API also has several pieces of advice to drivers who want to get the most of their motor oil and engine performance. 

How To Get More From Your Motor Oil:

  • First and foremost, it is crucial to follow the recommendations of the vehicle manufacturer regarding what type of motor oil to use and how often the oil should be changed. Motorists should use the recommended oil viscosity and ILSAC or API performance standards.
  • If drivers mix brands of oil, they should use the same viscosity grade and API service category to maintain performance.
  • Drivers should look for the API Certification Marks when they buy motor oil.
  • Drivers should ask for API-licensed motor oil every time they have their oil changed.
  • By properly disposing of their used oil, drivers could make a difference by recycling the used oil from their cars, trucks, motorcycles, or lawnmowers. If people change their own oil, they could take it to a collection center for recycling. If a car service outlet changes your motor oil, the outlet would typically take it for recycling, but if you are not sure, ask if this is the case. Used oil can be re-refined into the base stock for lubricating oil, so by recycling used motor oil, people can conserve energy and prevent pollution.

There are many different motor oils on the market. Motor oils can be mineral (or conventional), full synthetic, or synthetic blend. Each of those motor oils is designed for specific engines and various performance enhancements. The type of engine (gasoline or diesel), the type of vehicle (passenger car, caravan, truck), and the typical driving conditions (city driving, harsh winter, summer heat), usually determine which motor oil is best for the vehicle. Drivers should follow the recommendations of their vehicle manufacturer and ask a specialist if unsure, in order to maintain optimal engine performance and improve fuel economy.

By Tom Kool of Oilprice.com

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