We’ll take a closer look at the differences between these motor oils and give you information on which one is right for your vehicle. We take the confusion out of oil viscosities.

Oil Differences 10w30 vs 10w40

The quick answer is that 10W40 is a thicker motor oil than 10W30 at higher temperatures. They both have almost the same properties and the only difference is the viscosity of the oil.

Unfortunately, that quick answer doesn’t make it any easier to understand. You first need to know what the oil’s viscosity is and what the numbers on both engine oils mean.

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Understanding Oil Viscosity

When we talk about viscosity, it is known to be related to the thickness of a liquid. For example, oil is thicker than water. If you poured water and oil at the same speed, the water would flow faster. As a result, oil has a higher viscosity than water.

Viscosity is affected by several factors, especially when it comes to different types of motor oil. One of those factors is temperature. If you kept your oil in the fridge for many days, it would eventually turn into a waxy substance. Because this is true, you know that the viscosity and temperature of the oil are closely related. As the temperature increases, the viscosity of the oil decreases. In return, when the temperature drops, the viscosity of the oil increases. The two are proportional.

Your car’s engine needs the right oil viscosity to function properly. The oil must be able to withstand different temperatures and be able to adapt to any situation it is in. If your engine produces an excessive amount of heat, the oil can quickly become too thin and fail to protect the internal components. On the other hand, when the engine is cold, the oil can become too thick to flow properly.

That’s where oil grades come into play. Each is named based on its viscosity and how it will work.

Understanding Oil Quality

Both oils start with the number 10. This first number indicates the viscosity of the oil at low temperatures. Usually this number is assigned to winter temperatures. As this first number goes down, it flows more easily in cold weather. That’s why oils that start with the number 5 spill faster than those with the designation 10. Unsurprisingly, W stands for winter.

So what does the second digit in the oil class indicate? Shows how easily engine oil flows at optimum engine temperatures or during the hottest months of the year. The higher this number, the more protection the oil offers against extreme heat and pressure.

With this in mind, the only difference between 10W30 and 10W40 oil is the viscosity at higher temperatures and more pressure. 10W40 gets thicker as the temperature rises.

When to use 10W30 oil?

If you live in a cold climate, you will find that 10W30 works best for your vehicle. In these climates, motor oil only provides heat to the engine, not additional stress on the environment. 10W30 engine oil can also lower the temperature of the engine as it warms up in winter.

You will find that 10W30 is used more often than 10W40. It is also easier to find and cheaper. If you are looking for a cheap solution, you may prefer 10W30. However, you won’t want to use it if you live in hot climates or if it’s the middle of a hot summer.

When to use 10W40 oil?

If you live in a place where it is warm all year round, you prefer 10W40 motor oil. It is designed to perform better at higher temperatures and protect your engine from extreme wear. In addition to being more resistant to ambient heat, this oil is designed for engines that run hotter than others.

With this in mind you can still add 10W30 in hot weather, but keep in mind it will thin out faster than 10W40. As the temperature continues to rise, it may not lubricate internal components as well. Spend a little more to be on the safe side and use 10W40 for better protection against high temperatures.

Blend of 10W30 and 10W40 motor oils

If you search online for blending oils, many people will tell you it’s fine. However, it is not recommended for several reasons.

First, mixing types of engine oil can cause a drop in oil pressure as the engine accelerates. This problem can cause a bearing to fail due to rotation.

Mixing motor oils can also void your vehicle’s warranty. While both work the same in cold temperatures, one is designed to be thicker in warmer climates. Unless there is an emergency, it is not a good idea to mix oils and cause additional wear on the engine. By carrying motor oil with you, you can avoid this situation.