Have you ever wondered about designations like 5W30, 15W40, or 10W40 on engine lubricant bottles? What do they signify, and why are they crucial when selecting engine oil? These figures represent the engine oil’s viscosity grade, which indicates the lubricant’s fluidity and operational efficiency across varying low and high temperatures.1 This guide will clarify the different types of vehicle lubricant grades and their meanings – here, we’ll explain viscosity grades in detail.
What Exactly is the Viscosity Grade of Engine Oil?
The viscosity grade of engine oil conveys information about the oil’s resistance to flow within the engine.2 A lubricant with a lower viscosity grade will be more fluid, less dense, and will circulate more readily.3 Conversely, a higher grade signifies a thicker oil, which flows slower, aiding in the formation of a protective film over engine components.4
Given that engine oil’s properties are affected by temperature, its grade provides insights into how the lubricant performs and flows in both hot and cold conditions.5 For instance:
- In low temperatures, it’s advisable to select an oil with a low viscosity grade. This facilitates the lubricant’s circulation within your vehicle during a cold engine start.
- Engine oil with a higher grade will exhibit greater resistance in the hotter, more sensitive parts of the engine. Being thicker, this oil will establish a protective film on engine components, diminishing wear and preventing damage by reducing friction between parts.6
Choosing the appropriate viscosity grade, and consequently the right engine oil, is paramount for ensuring your vehicle operates smoothly. Oil plays a vital role in cooling your engine, lubricating its parts, and preventing friction and potential damage.7 Additionally, engine oil aids in removing impurities and effectively inhibits the formation of corrosion and rust.8
What Are the Different Viscosity Grades of Engine Oil?
How do you determine the correct viscosity grade for your vehicle? The Society of Automotive Engineers (SAE) has devised a system for categorizing oils based on their viscosity grade at both low and high temperatures.9
Monograde Oils
Monograde oils are designed for use within a relatively narrow temperature range and are generally intended for older vehicles.10 This type of oil falls into two subcategories, depending on the season in which the vehicle is operated.11
For colder, wintry months, opt for an oil marked with the letter ‘W’, which stands for ‘winter’.12 These include SAE 0W, 5W, 10W, 15W, 20W, and 25W engine oils. Their viscosity grade is low, indicating they are particularly fluid lubricants.13 Each category is defined by its viscosity at a specific temperature (ranging from -10°C to -35°C, depending on the grade). When cold, the more fluid the lubricant, the less effort is required from the oil pump during engine start-up.
To protect your engine during warmer months, it’s best to choose an engine oil with a high viscosity grade that is not marked ‘W’.14 These are SAE 8, 12, 16, 20, 30, 40, 50, or 60 engine oils. A higher viscosity grade (thicker oil) will ensure the engine is adequately protected and sealed in warm weather.15 However, this may come at the expense of the superior lubrication and fuel-saving capabilities offered by lower-grade oils.
Multigrade Oils
Multigrade oils are perfectly suited for modern vehicle models, making them the most widely used oils today.16 They offer the significant advantage of performing effectively across all seasons, regardless of the ambient temperature, because they are less susceptible to temperature fluctuations than monograde oils.17
Containers of multigrade lubricants feature a number on either side of the ‘W’ to indicate the oil’s capacity to handle seasonal temperature variations, such as 5W30, 15W40, or 10W40.18
What do these viscosity grades signify? As with monograde oils, the ‘W’ still denotes ‘winter’.19 The number preceding this ‘W’ represents the winter viscosity grade – the engine’s ability to start even at low temperatures.20 A lower number indicates an easier cold start for the engine; therefore, for faster start-up, you should choose a more fluid oil.21
The value following the ‘W’ represents the engine oil’s viscosity grade at high temperatures.22 A higher grade means optimized component protection and engine sealing, as a thick layer of oil forms in the hotter, more critical areas of the engine.23 Conversely, a lower number will be more effective at reducing friction between hot parts and improving fuel consumption.
If you have any uncertainty when selecting the viscosity grade for your engine oil, consult your vehicle’s owner’s handbook, seek advice from a professional, or utilize Total’s oil search and reference tool, LubConsult.
For more information on engine oil or to explore TotalEnergies’ range of automotive lubricants, please refer to their official resources.