Engine Oil Numbers Explained

While most car owners and enthusiasts are aware of what oil their car requires — or, at the very least, know where to check when the time comes — it isn’t always obvious to most people exactly what the numbers mean, or why it is so important to use the correctly labeled engine oil. Besides the different types of oil, such as synthetic, high-mileage, or specialty oils, the numbers on the engine oil bottles, typically expressed as ##W##, are universal. 

What do the numbers on motor oil actually mean?

The numbers that represent different types of engine oil refer directly to the fluid’s viscosity. It’s important to start by noting that engine oil is used as an internal lubricant for the many moving internal components of the engine. As engines range in temperature from their lower starting temperature to their higher operating temperature, the oil, which, like any liquid, changes in viscosity. 

These numbers, in most vehicles, look like a 5W20 or a 10W30, where the first number refers to the grade or viscosity of the oil at the colder end of operation, and the second number refers to the viscosity of the oil at the higher operating temperature. 

Most modern-day vehicles rely on this system as it allows for the proper range of oil viscosity require to maintain optimum engine performance, but there are also straight-weight oils that are offered at a single viscosity. These are more typically used in classic cars and it is not recommended to use them in your modern vehicle if it is not what is called out in the user manual…but that’s a story for another article. 

Can you use a different engine oil than recommended?

There are several circumstances under which you may need to use a different engine oil than is recommended for your car from the factory. For example, if your vehicle has any performance modifications it may be recommended to use a different viscosity of oil. This is information your vehicle performance shop or tuner will advise on. 

In some circumstances, such as some older German cars, you may notice that your vehicle burns or “consumes” oil at various paces, and can leave you with an “oil level low” warning that causes you to pull over at a gas station and pick the closest option available. 

The third situation you may face with engine oil changes is if your vehicle operates in extreme temperatures outside of typical engine oil parameters, such as extreme heat or extreme cold. In this case, it may be beneficial to run a different oil viscosity.  

What happens if you use thicker oil than recommended?

READ MORE: FIRST OIL CHANGE on my C6 | Reckless Raquel

Using thicker oil than recommended for your engine can reduce fuel economy and, in extreme circumstances, reduce the life expectancy of your engine. A thicker oil may be used for high-heat-producing engines. For example, the Dodge Viper, although it is a standard gasoline 8.30-liter V10 engine, uses diesel-grade engine oil. In some circumstances such as extreme heat with long driving durations, a thicker oil may be recommended. 

What happens if you use thinner engine oil than recommended?

Using thinner oil than recommended can mean that the oil isn’t performing an optimal job at lubricating the engine’s internal components, causing unnecessary wear and, as a result, also reducing the life expectancy of your engine.

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