10W40, 15W40, and 5W30 are common designations users come across when selecting engine lubricants. These figures signify an engine oil’s dedicated viscosity grade, which refers to the lubricant’s efficiency and fluidity levels.

To help owners find the right viscosity grade for their vehicle, the Society of Automotive Engineers, (SAE) developed a system that classifies oils according to the viscosity grade they possess at both low and high temperatures.

In this blog, we’ll look at some of the different viscosity grades available for monograde and multi-grade oils.

Monograde oil

Monograde oils are typically used within a relatively narrow temperature range and are usually formulated for older vehicles. This oil type is split into two categories, that relate to the time of year that the vehicle is being used in.

For engine care in warmer months, owners should select an engine oil with a higher viscosity grade that does not feature a ‘W’. For example, engine oils like SAE 8, SAE 12, SAE 16, SAE 20, SAE 30, SAE 40, SAE 50, or SAE 60. A higher viscosity grade means a thicker oil and will ensure that the vehicle engine is adequately sealed and protected in warm weather.

Multi-grade oil

This oil type is ideally suited to modern vehicle models. As a result, multi-grade solutions are the most popular engine oils in use today. They can work effectively in every season, regardless of outside temperatures, as they are less impacted by variations in temperature than monograde oils.

Multi-grade products are marked a number on both sides of the letter ‘W’ to display the oil’s capability with seasonal temperature variations, for example 5W30, 15W40, and 10W40.

The ‘W’ refers to ‘winter’ and the number before it represents its winter viscosity grade. This means the engine’s ability to start at low temperatures in colder weather. The lower this number is, the easier it will be for the vehicle engine to manage a cold start. For a quicker start-up, users should select a more fluid oil.

The number following the “W” denotes the engine oil viscosity grade working at high temperatures. A higher-grade means optimised engine sealing and component protection, as a thicker layer of oil will be formed within the engine’s hotter and more critical areas. However, a lower number after the “W” will mean that the oil is more effective in decreasing friction between heated parts and will improve fuel consumption.

To select the correct engine oil viscosity, always consult the vehicle handbook for your make and model.