Viscosity classifications: what are they and what’s the meaning behind them?

At first glance, the combination of numbers and letters attributed to an engine oil can be confusing. However, this mix of characters represents some vital information about the characteristics of each specific engine oil.

Put simply, viscosity describes the ease with which an engine oil flows. As a general rule of thumb, engine oil specifications and engine oil specification charts usually list the engine oil viscosity on the product description and packaging.

What does each viscosity classification mean?

The viscosity of an oil is measured by its resistance to flow. For an engine oil, two numbers define the viscosity grade – the first number goes before the letter 'W', which stands for winter, and is related to how an oil flows when it is cold, such as at engine start-up. Following this, the second number is defined by how oil flows at normal engine operating temperatures.

In a nutshell, the smaller the number, the better the lubricant will flow. For instance, a 5W-30 oil will flow better than a 10W-30 oil at start-up temperatures. Similarly, a 10W-30 oil will flow more easily than a 10W-40 oil at normal engine operating temperatures.

It’s important to understand that engine oils naturally thicken as they cool and thin as they are heated. Thin, low viscosity oils generally offer better protection to engine parts at cold temperatures, whereas thick, high viscosity oils tend to be better at protecting engines at higher temperatures. However, if an engine is designed to be used with lower SAE grades, an SAE-0W-20 oil, for example, can protect the engine as well as an SAE 5W-40 engine oil.

Oil viscosity can have a significant impact on an engine’s performance. When assessing viscosity, keep in mind:

• If the oil is too thin, it may not provide adequate lubrication – especially at operating temperatures – leading to a greater chance of engine wear
• If the oil is too thick, it may not flow properly to lubricate all the necessary parts. This is especially a concern at cold temperatures, when viscosity increases and lubrication may be delayed.
  

How Texaco Lubricants’ Product Selector can help

Every vehicle has a specific oil viscosity recommended by its original manufacturer, which is why choosing the correct car engine oil is crucial for a vehicle’s health and efficiency. Though this can sometimes be a confusing process, Texaco Lubricants’ Product Selector is an easy-to-use online tool that recommends the most suitable options for a vehicle’s exact make and model.

In some cases, the Product Selector may recommend an alternative viscosity – such as 5W-30 instead of 10W-30 – when it meets or exceeds the required performance specifications. This ensures flexibility without compromising engine protection or efficiency.

The verdict: Are viscosity classifications important to understand?

Put simply, yes. Engine coolants play a crucial role in maintaining your vehicle’s health and performance. They are essential for regulating engine temperature, helping prevent overheating, and helping protect the engine components from corrosion and wear.

Without a doubt, it is vital that viscosity classifications are understood. There is no use in topping up a vehicle’s oil with a product of an incorrect viscosity, as this could lead to serious engine damage, reduced fuel economy, and even engine overheating. 

If unsure, users should always refer to the recommended oil viscosity for their vehicle, which is specified in the owner's manual.