10w 30 vs 10w 40: What’s the Difference & Which Is Better?

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When it comes to vehicles, the number of types of engine oils available can be superbly overwhelming. Rows and rows of bottles, all offering different claims and features to make your choice even harder. 

For a car owner who comes to the wrong choice of lubricant, it may cause engine damage. Furthermore, customers also need to consider if the oil type is compatible with their vehicle. That’s why it’s always safer to go for a type which is recommended by car companies.

When comparing engine oils, there are a lot of other factors to take into consideration such as the cost, climate, driving conditions, the internal components, mileage and more.

Without further ado, let’s take a look at both 10w 30 and 10w 40 engine oils.

What Is The Difference Between 10W30 and 10W40?

The major difference between these two oils is the viscosity rating. The higher number shows that it has less viscosity than the lower rating oil. Another difference is the cost where the 10W40 is usually more expensive than 10W30

10w30 Vs. 10w40: Which One Is Better?

Determining which one oil to use can be a little tricky. Each has its own advantages and disadvantages, and choosing the right one means that your car will run smoothly and without any problems.

10W-30 is designed for low temperatures and it is produced for reducing fuel consumption. It is usually used in cold seasons when the temperature reaches below zero degrees Celsius. By contrast, 10W-40 is an excellent choice as well as it offers great benefits such as high performance, protection against rusting and sludge. As a result, 10W-40 is one of the most popular engine oils in the world. However, the oil is not designed for low-temperature conditions (below zero degrees Celsius)

What Does The “10” Mean In 10w30 And 10w40?

It means that that the oil has a viscosity of 10 when it’s at a temperature of 30 degrees Celsius. On the other hand, if you’re looking for an oil to use in colder weather, you’ll want one with a number lower than 30. The lower number represents less viscosity or thickness at those temperatures.

The lower the numbers, the thinner and more easily pumped through the engine seals as well as being able to better reach components such as gears within an engine that tend to run hotter than its surroundings. This is because engines heat up during operation and reach high operating temperatures. These factors help reduce heat and deliver outstanding lubrication during extreme pressure and shear conditions.

What Does The “W” Represent In 10w30 And 10w40?

Commonly misjudged, the “W” actually stands for “winter.” This refers to how well an oil can protect your engine from extreme temperatures during cold weather conditions (below 32 degrees Fahrenheit). Depending on the climate you live in, a lower number can provide better protection when temperatures drop.

Defining Viscosity

The Viscosity Index (VI): Viscosity is the measure of how thick or thin a fluid is, and the measurement used depends on what particular application you are measuring it for. As an example, corn syrup has a higher viscosity than water because it is thicker.

Viscosity is measured in an index known as cST (centistokes), which is “a unit for measuring the flow behavior of liquids at low differential stress”.

Centistoke is simply a measurement of viscosity used to compare between different fluids. For example, motor oil has very high viscosity because it needs to be able to withstand high amounts of pressure in an engine.

This is why the viscosity of motor oils is rated based on temperature, with low numbers at cold temperatures and higher numbers at hot temperatures. This enables the oil to work more effectively depending on what the outside temperature is like.

When To Use 10w30 Motor Oil?

10w30 Motor Oil is perfect for use in cold seasons, especially during the winter. They can provide excellent protection for your car engine when it drops below 32 degrees Fahrenheit or below 0 degrees Celcius.

When To Use 10w40 Motor Oil?

10w40 Motor Oil is perfect for use in warm seasons, especially during the summer. They can provide excellent protection for your car engine when it climbs above 95 Fahrenheit or 35 degrees Celcius.

How Is Motor Oil Graded?

Motor oil is graded based on its viscosity. The higher the number, the lower the viscosity of the oil and vice versa for a lower number. Grading does not refer to the oil’s weight. Water is a lower grade than motor oil, while a 60 wt motor oil is heavier than 50 wt motor oil. Motor oils graded based on their usage in cold temperatures and hot temperatures.

10w30 and 10w40: Which Oil Suited to Your Vehicle?

If you experience a cold climate in your area, 10w30 is perfect for you. It was designed to provide excellent protection at low temperatures. For hot weather conditions, on the other hand, you need an oil with high-temperature viscosity like 10w40.

10w30 Vs. 10w40: Which Is The Better All-Purpose Option?

When talking about which oil is better as a general all-purpose option, 10w30 oil is the better of the two. This is because it can provide great protection at both low and high temperatures. In fact, most manufacturers produce engines that run with a 10w30 weight oil in them to ensure optimum engine performance for almost any condition.

Proper Way Of Mixing 10W30 and 10W40 Motor Oils

Even though mixing sounds like a perfectly reasonable option, it is highly advised that you do not. Mixing can cause poor performance and may even damage your engine in the process. The reason for that is the way viscosity works.

10w30 and 10w40 motor oils both have very different viscosities, which means that it is difficult for them to mix. Higher temperature oil (10w40) does not mix well with lower temperature oil (10w30) and eventually separates into its own layers once your engine starts operating again. This can cause the viscosity of both oils to change, leading to poor lubrication. Excessive wear may also result from mixing these two types of oil.


With all this in mind, it is important to find a middle ground where there is a compromise of price and performance. This allows you to get a product that is more durable and at the same time, more cost-efficient as you will be able to use it for a longer period of time.

10w30 and 10w40 motor oils have their own benefits and disadvantages. However, it’s up to you to decide which one suits your vehicle best so that you can get the most out of your engine.

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