Decoding Engine Oil Numbers

all about engine oil bottle numbers

  • Engine Oil Numbering Based on Viscosity
  • API Service Classification of Engine Oils
  • ACEA Specifications
  • FAQs

The engine oil serves as a vital fluid for your car’s engine, ensuring its smooth operation and longevity. When you stroll down the automotive aisle of a store, you’re likely to be confronted with a myriad of engine oil options, each labelled with a combination of numbers and letters. Understanding these engine oil numbers is essential for selecting the right oil for your vehicle. 

Let’s explore what the numbers on engine oil bottles mean, understand their implications for the oil’s properties and how they can guide you in making informed choices.

oil with spcecific engine oil number being filled in car
The engine oil bottle numbers are alpha-numeric codes which indicate an oil’s functionality and nature

What Do the Engine Oil Numbers Mean?

The alpha-numeric code on the car engine oil bottles indicates the oil’s nature and function. Here, we’ve outlined the criteria for characterising and differentiating engine oils.

Engine Oil Numbering Based on Viscosity

The most prominent numbers on an engine oil bottle refer to its viscosity, a measure of the oil’s resistance to flow. Multi-viscosity motor oils feature a set of two engine oil numbers. The initial set (0, 5, 10, 15 and 25) reflects the oil’s low-temperature flow, with a smaller number indicating better flow, followed by the ‘W’, denoting the winter grade. 

The second set indicates high/operating temperature flow; for instance, 10W-30 oil flows better than 10W-40 at normal operating temperature.

If the grade lacks ‘SAE’ or the ‘W-’ between the numbers, it might not be a multi-grade. For instance, a 5-30 is not a multi-grade oil.

Let’s explore some globally used engine oil grades:

  • 0W-20: Starts with a thinner viscosity (0) when cold, transitioning to thicker viscosity at normal operating temperature.
  • 0W-30: Behaves as a 0-weight oil at the start and increases in viscosity at normal operating temperature.
  • 0W-40: Acts as a 0-weight oil initially and transitions to a heavier, 40-weight oil at normal operating temperature.
  • 5W-30: This oil is suitable for colder climates, as the ‘5W’ indicates its flow characteristics in winter. The ’30’ signifies its viscosity at higher temperatures, making it versatile for a vast range of driving conditions.
  • 5W-40: Fully synthetic, performing like a 5-weight oil during cold starts and a 40-weight oil at normal temperature.
  • 10W-40: It has a slightly higher viscosity at both low and high temperatures compared to the 5W-30. This makes it a better choice for warmer climates or older engines that demand a thicker lubricant.

API Service Classification of Engine Oils

The American Petroleum Institute (API) classifies engine oil numbers based on the type of engine, with ‘S’ for petrol and ‘C’ for diesel. The letter following denotes the oil’s standard, with higher alphabet letters indicating newer and better standards, for example, SN > SL. 

Diesel engine oils may have sub-standards like CF-2 and CH-4. Choosing oil with a higher standard than the engine’s requirement is acceptable, however, it must be noted that when opting for higher standard oil, only the neighbouring one should be used, for instance, SM instead of SL. That said, using lower-standard oil can lead to accelerated wear which is also a sign of wrong car oil usage.

Petrol engine oil grades include:

  • SG – Introduced earlier than 1993
  • SH – Introduced in 1993
  • SJ – Introduced in 1996
  • SL – Introduced in 2001
  • SM – Introduced in 2004
  • SN – Introduced in 2010

Similarly, each diesel engine oil grade meets specific emission and performance criteria. Some examples of these are:

  • CC – for light engines
  • CD – for four-stroke engines
  • CD-II – for two-stroke engines
  • CE – for those low engines working under heavy load
  • CF – a better standard than CD diesel oil
  • CF-4 – a better standard than CE standard diesel oil 
  • CF-2 – a better standard than CD-II diesel oil
  • CG-4 – a better standard than CD, for low emissions 
  • CH-4 – replacement standard for CD 
  • CI-4 – Introduced in 2002, a replacement for CD, CE CF, CG and CH standards
  • CJ-4 – better for engines with enhanced exhaust cleaning
choosing between engine oils based on their codes
Understanding the engine oil numbers is important to make well-informed decisions for your car

ACEA Specifications for Engine Oils

ACEA (European Association of Automotive Manufacturers) has its classification, categorising oils into:

  • A/B – for petrol and diesel engines in light commercial cars
  • C – indicates low SAPS (Sulphated Ash, Phosphorus and Sulfur) or low ash. These oils are essential for vehicles with particulate filters and advanced catalytic systems. They extend the lifespan by minimising ash deposits on the filters or catalysts, preventing clogging.
  • E – oil grade for trucks with diesel engines.


Which one is better, 5W-30 or 5W-40?

Opting between the engine oil numbers – 5W-30 or 5W-40 depends on multiple factors, including your car’s model year, engine and driving habits. That said, for urban driving, frequent traffic, high speeds and older cars, opt for 5W-40. On the other hand, if you prioritise calm driving, fuel economy and eco-friendliness, go for 5W-30.

What is the difference between 0W-30 vs 5W-30 oil grades?

The primary difference between 0W-30 vs 5W-30 oils lies in cold-start viscosity. 0W-30 is thinner at startup and beneficial in extremely cold temperatures. Whereas, 5W-30 is slightly thicker initially but still provides good cold-weather performance. Both transition to similar viscosity at operating temperature. Moreover, here is another comparison of racing vs regular oil to help you differentiate between the oil’s requirements for racing and street cars.

What are the different types of car engine oil?

There are primarily four types of car engine oils, varying in viscosity and quality levels. They include: 

  • Mineral oil
  • Synthetic oil
  • Semi-synthetic oil
  • High-performance oil

What does the Total Base Number (TBN) in oils mean?

Total Base Number (TBN) in oils represents their alkaline reserve for neutralising acidic elements. It indicates the oil’s capacity to counteract acids formed during combustion, preventing corrosion and ensuring prolonged engine protection. 

The Total Base Number (TBN) lies between 7 to 10 for petrol engines and 10 to 14 for diesel engines. When the TBN decreases, reaching around 3, it can no longer neutralise acids, indicating the need for an oil change.

With this, we have the engine oil numbers explained along with their classification. The numbers on engine oil bottles empower consumers to make informed decisions tailored to their vehicles and driving conditions. Whether you’re facing sub-zero temperatures or scorching summers, selecting the right viscosity and type of oil is crucial for maintaining optimal engine health. Moreover, here are some engine oil myths for you to acknowledge, that are no longer true.

Besides, if you are looking for other car tools, here is a wide range of car parts and accessories for sale in the UAE.

For more information on different car fluids, stay connected to the dubizzle auto blog.