5W 40 Vs 15W40

Engine oil is the lifeblood of your vehicle’s engine. It keeps the engine components lubricated, protects against wear and tear, and also helps to maintain the engine’s peak performance. One of the most important decisions that every vehicle owner faces is selecting the right engine oil. The two most commonly used engine oils are 5W-40 and 15W-40. In this article, we will compare the two and help you determine what kind of oil your engine needs.

What is 5W-40 Oil?

5W-40 is a fully synthetic engine oil. It is a thinner oil than 15W-40, meaning it offers better fuel economy and superior cold-weather performance. The number 5W indicates the viscosity of an oil in cold temperatures, and the number 40 refers to its viscosity at a high temperature.

Viscosity refers to the thickness of the oil. The higher the viscosity number, the thicker the oil. 5W-40 oil is the perfect oil for engines that demand quick starts in cold weather, especially for diesel engines. This oil is also ideal for high-performance gasoline engines that require enhanced engine protection under all temperatures.

What is 15W-40 Oil?

15W-40 is a multi-grade mineral-based oil consisting of a base oil and additives that make it suitable for various conditions. It consists of a thicker base oil than 5W-40, which provides better protection to older engines that do not require high-performance oils.

Unlike 5W-40, 15W-40 is not a synthetic oil. However, it offers excellent protection and lubrication for diesel engines with or without turbochargers. It is also ideal for gasoline engines that require high-mileage engine protection.

5W-40 vs. 15W-40: Which One is Better?

The answer to this question depends on several factors, such as the type of engine, driving conditions, and the climate. Here are some points to help you decide which one is better:

Engine Type:

If you have a newer engine, 5W-40 is the best oil for you, as it provides superior protection under all conditions. On the other hand, if you own an older engine with high mileage, 15W-40 is the better choice. This oil is thicker, providing more protection to older engines that experience oil consumption and sludge buildup.


If you live in a cold climate, 5W-40 is perfect for your engine, as it offers better cold starting, which is crucial during icy and freezing conditions. However, those who live in warmer climates can use 15W-40, as it offers excellent protection at high temperatures.

Driving Conditions:

If you drive your car under heavier loads or do a lot of towing, 5W-40 is ideal for your engine. The thinner oil provides better fuel economy and protection under extreme driving conditions. For light-duty vehicles, 15W-40 is more than satisfactory as it offers protection and durability to the engine.


Which one is better for gas engines: 5W-40 or 15W-40?

If you have a high-performance gasoline engine, 5W-40 is the best oil for you as it provides superior protection and lubrication. For older, high mileage gasoline engines, 15W-40 is the better choice for protection.

Which one has a higher viscosity: 5W-40 or 15W-40?

15W-40 has a higher viscosity than 5W-40, providing more protection to older engines needing a thicker oil.

Which is better for cold weather: 5W-40 or 15W-40?

5W-40 is better for cold weather as it provides better cold starting, making it ideal for areas with freezing temperatures.


Choosing the right engine oil gives your engine a longer life and better performance. With so many options available on the market, it’s easy to get confused. By understanding the differences between 5W-40 and 15W-40 oils, you can make an informed decision. Both oils perform well in different conditions, so always go with the one that suits your engine’s needs.