Multi-grade engine oil

What Is Engine Oil Nomenclature or Numbering System?


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What is SAE-30 or Mono-grade engine oil?

This type of oil is known as single-viscosity or mono-grade engine oil. Earlier generation engines used a common oil (which was SAE-30 grade) throughout the year. However, mono-grade oils work well only when the ambient temperatures are steady such as in the summer. Mono-grade oils become thin as they get heated and become thick as they cool down. Also, a mono-grade oil DOES NOT use any additives such as a polymeric Viscosity Index Improver also known as Viscosity Modifier.

Castrol SAE-30 mono-grade engine oil
Castrol SAE-30 mono-grade engine oil

Society of Automotive Engineers (SAE) has developed numerical coding system to grade the engine oils according to their viscosity. SAE viscosity index includes the following numbers: 0, 5, 10, 15, 20, 25, 30, 40, 50 and 60. As a thumb rule, lower the number means lower viscosity and vis-a-vis.



What is 10W-40 or Multi-grade engine oil?

This type of oil is known as multi-viscosity or multi-grade engine oil. It means that this oil is suitable for use over a wide temperature range. The first number represents the temperature index of the oil i.e. the coldest temperature at which it can pass or start flowing. It shows the viscosity rating of the oil. This means, 10W-40 oil can flow at 10 degrees Celsius. Similarly, the 5W-40 oil can flow at 5 degrees Celsius.

Motul 10W-30 multi-grade engine oil
Motul 10W-30 multi-grade engine oil

Multi-grade oil has dual properties. The second number represents its viscosity at 100 degC i.e. 40. The second number actually shows the viscosity (thinness/thickness) of the motor oil. Viscosity grades for engine oil range from 20, 30, 40, 50, to 60.



Here, higher the number thicker is the oil. This simply means the 10W-40 oil is thicker than 10W-30 oil. Similarly, a 5W-50 is thicker than 10W-40 engine oil. However, it can flow at a much lower temperature of 5 deg Celsius.

Multi-viscous engine oil provides better winter operation, fuel economy, and engine durability. It also helps reduce the wear and tear of engine parts during extreme weather conditions.

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