Motor Oil Classification Explained | Motor Oil API Ratings And SAE Grades

Motor oil, AKA Engine oil, is a critical lubricant in your car or truck. The right oil helps to prevent engine parts from wearing, corrosion and overheating. Furthermore, it improves gas mileage and keeps your vehicle running at its best performance.

Choosing the right engine oil is complicated. Generally, these oils have two different classifications: SAE grading and API ratings. API motor oil standard awarded by American Petroleum Institute and SAE is granted Society of Automotive Engineers. You have to check these ratings before purchasing new motor oils. It helps to decrease engine knock, reduce metal parts wearing, improve performance and reduce emission.

This article explains motor oil classifications. How to choose the best oil for your engine for best performance.

What is API in motor oil?

The American Petroleum Institute classifies motor oils based on their ingredients (detergents and other chemicals additive), emission standards, engine manufacturer’s requirements, and fuel economy. For this API service classification, the institute performs series of tests like valve train wear, low-temperature sludge, oxidation, bearing corrosion, fuel economy, chain wear, and Low-speed pre-ignition (LSPI). This classification is available for mineral, semi-synthetic, and synthetic oils types. Engine manufacturers periodically introduce new motor oil requirements, and as a result, new oil service classifications are introduced.

Every motor oil has many chemicals like zinc, phosphorus, molybdenum, magnesium, and calcium. Different categories of lubricants have different levels of ingredients. For example, API SN Plus uses more magnesium and less calcium than API SN oil.

This API lubricants standard uses the two-letter code system for this ranking. There are two separate classifications for gasoline and diesel engines. The service classification code starts with the letter “S” for petrol engines and “C” for diesel engines. The higher the second letter, the more recent API category it has. You can find this rating on the back label with the “API Service Symbol Donut.” (the initial gasoline engine motor oil classification is “API SA,” which is now absolute).

The latest API grade lubricants are backward compatible with previous grades. For example, the API SN grade is compatible with API SM recommended gasoline engines.

What is Motor Oil SAE Grading?

The SAE grading offers by the Society of Automotive Engineers (SAE). This engine oil standard is given based on motor oil viscosity grade. The viscosity is the fluid’s resistance to flow. Thicker oil provides better protection at high operating temperatures than thinner motor oil. However, thicker motor oil flows slowly at cold temperatures, so denser lubricants increase the friction of the engine’s moving parts at cold engine startup. This rating is available for conventional, semi-synthetic, and synthetic oils.

The SAE grading has two types. It is mono-grade (e.g., SAE 40) and multi-grade (e.g., 10W-30). Multi-grade motor oils work in both cold and hot temperatures without sacrificing performance. It is ideal for most driving conditions.

Single-grade motor oil codes use two-digit numbers, while multi-grade motor oils display numbers with the letter “W,” for example, 10W-40. In multi-grade motor oils, the number in front of the letter “W” indicates the cold temperature viscosity grade; The letter “W” stands for “Winter,” and the last two digits are the viscosity at 100°C/212°F temperature.

Smaller numbers of oil flow easily because they are thinner. A thicker liquid has a higher viscosity; such a thick fluid has a higher resistance to flow. The thickness of fluids changes as their temperature change.

Motor Oil API Ratings Vs SAE Grades.

API and SAE ratings for motor oils are two distinct classes. When purchasing new motor oil, you must check the API ratings and SAE grade. The API service classification rate the motor oils base on their ingredients (detergents and other chemicals additive), while the SAE grades rate the oil based on viscosity. The API classification is important because it ensures that your oil meets the Original Equipment Manufacturer’s (OEM) recommended performance level, fuel economy, and latest exhaust emission standards. The lubricant’s viscosity is important because it specifies its film strength and efficiency in reducing friction in the engine’s moving parts. 

One API rating contains different SAE motor oil grades and similarly, one SAE grade comes under different API ratings. For example, API SP has SAE 0W-10, SAE 10W-40, and SAE 15W-30. and SAE 10W-40 come in different API service categories.

Therefore, when purchasing new motor oils, check the bottle label’s API Service category and viscosity grade. You can easily find these details on the API service symbol donut. You must use the correct API rating class and SAE grade recommended by the vehicle’s manufacturer to improve gas mileage, wear protection, reduce exhaust emission, and reduce deposits and sludge build-up on pistons and turbochargers.

API Service Classification for Gasoline Engines.

American Petroleum Institute (API) introduce several API categories for gasoline engine motor oil over time. Initial classes are now absolute; you must choose the car and truck owner’s manuals recommended categories. The latest API categories have the earlier categories’ performance additives. Thus, if your truck’s or car’s owner’s manual specifies an absolute oil grade, you can safely use the most modern oil grade without sacrificing performance.

API Service Classification for Diesel Engines.

There are mainly two categories of American Petroleum Institute API rating for diesel motor oil, denoted by the letters C and F. These two categories of oils are not interchangeable or backward compatible. The latest oil provides better withstanding in high temperatures, prevents deposit protection for pistons, seal compatibility, and reduces sludge control.

FAQ.

Which is better, API SN or SP?

API SP is the latest motor oil API service category introduced in May 2020. API SP is better than the API SN, and this oil category is fully backward-compatible with older API service categories. API SP has additives to improve fuel economy and protect engine parts.

What are the 3 oil classifications?

We can find mainly three types of motor oils on the market: conventional, full-synthetic, and semi-synthetic. The main difference between these three different motor oils is base oil. Conventional motor oil is made of crude oil (mineral oil), and synthetic motor oil is made from chemical synthesis. All these oils contain 80-90% base oil with performance booting additives like viscosity index improvers, anti-wear, detergent, corrosion inhibitors, and anti-friction.

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