What is the difference between these two types of motor oil? It really all comes down to how thick the oil is under different environmental conditions. This guide will quickly teach you everything you need to know about motor oil viscosity, what those numbers mean and ultimately when to use 5w30 vs 10w30.

What do the numbers mean in 5w30 or 10w30

Viscosity, in general, is a measurement for how much a liquid resists flow and comes in two forms. There is dynamic viscosity and kinematic viscosity, a measurement of these two attributes is what ends up on the label.

Dynamic viscosity refers to the amount of energy required to move an object through the given lubricant and is shown as the first number before the ‘w’ in an oil name. For example, in a 5w30 oil, the dynamic viscosity is shown with ‘5w’. This number also refers to the oil’s ability to flow during cold weather. For example, when comparing 5w30 vs 10w30, you should be able to see that the 5w30 oil will perform better in the cold.

Dynamic viscosity is measured through the Cold Crank Simulator test, which is a device used to determine the low-temperature performance of different oils when starting a cold engine.

Kinematic viscosity is a fluid’s resistance to flow and shear due to gravity. A lubricant with a lower viscosity flows faster, as there’s less resistance and shear induced onto it.

We can see this in an example by comparing the flow rates of two compounds with very different flow rates. If you filled a jar with water and another jar with honey and try to pour both out, there would be a clear winner. Water would win out no matter what, and this is due to the considerably lower viscosity water packs in.

The temperature grade of an oil is also determined by the kinematic viscosity it possesses. We can see this in the name by looking at an example oil, like 10w30, where the ‘30’ represents the kinematic viscosity.

What Oil Does My Motor Need? 

Low viscosity oil has a chance of being too thin for your vehicle, causing damage over time and may actually comprise the engine itself. This is due to the fact that a thinner lubricant cannot properly lubricate an engine. There are even more issues that can arise from lower than recommended oil viscosity in vehicles, such as the fact that when combined with extreme temperatures and physical pressure, the oil itself may fail to properly lubricate and prevent metal to metal contact within your engine. 

Using a higher viscosity oil than necessary is a mistake thousands of consumers make and causes immense amounts of damage to cars every year. Engines fueled with higher than necessary oil may become considerably less fuel efficient, and experience starting difficulties. Although thinner oils become considerably worse for your car during the heat of summer months, a higher viscosity oil starts to have more issues when combined with colder temperatures. As the temperature gets colder, the oil becomes thicker and can make starting your car nearly impossible! 

As you can see from the issues that arise when you use an improper oil, there’s a very heavy focus on choosing the right oil. The owner’s manual of your car is your best bet for finding properly fact-checked information on what oil to use for your car, and often time’s it will show you which oils to use during specific temperature windows, ensuring your car’s engine stays functional. 

When to Use Each Type of Oil 

5w30

5w30 is an oil most commonly employed in smaller and lighter duty diesel engines, gasoline engines, and some petrol engines. Due to the ‘5’ in its name, we can infer it provides a good amount of flow even in cold temperatures, making it the choice of many people.

The ‘5’ in its name means it has a lower viscosity than the other oil, making it more useful in harsher conditions. This form of oil has a working range from -30C to +35C, making it work for those that may be driving in extremely cold situations. 5w30 oil also allows engines to start with more confidence in colder temperatures as it is thinner! 

10w30

10w30 oil has a different aim and working range. It becomes thicker at lower temperatures, cutting its usable temperature down quite a bit. It is effective at -18C to +30C, worse margins than the ones provided by 5w30. 

This form of oil is most commonly used in heavier and larger engines that have to haul large loads across places, and rightfully so. 10w30 oil performs a much better sealing job than 5w30 oil, allowing these machines to run with considerably more confidence as it decreases the chances of a mechanical failure, which is important in the industries it is most commonly employed in.