5W-40 Vs 15W-40

Engine oils play a crucial role in maintaining the performance of a vehicle. The right oil can help extend the life of an engine and protect vital components from wear and tear. The two most popular oil grades used today are 5W-40 and 15W-40. In this article, we will discuss the differences between these two oil grades and help you determine which one is the right choice for your vehicle.

What is 5W-40?

5W-40 is a synthetic engine oil with a viscosity grade of 5 when cold and 40 when hot. The term viscosity refers to how easily the oil flows through the engine to lubricate moving parts. A lower first number (the W in 5W-40) means the oil flows more easily at low temperatures, which is important for cold starts. The second number (40) relates to the oil’s performance when the engine is hot, with higher numbers indicating better high-temperature protection.

Synthetic oils like 5W-40 are typically preferred over conventional oil due to their superior lubricating properties and longer lifespan. They contain fewer contaminants, are more resistant to heat, and function better in extreme temperatures. They also help reduce engine wear and prevent the buildup of harmful deposits.

What is 15W-40?

15W-40 is a mineral-based engine oil with a viscosity grade of 15 when cold and 40 when hot. Mineral oils are created from the distillation of crude oil and are less refined than synthetic oils. As a result, they tend to be less expensive but also have a shorter lifespan and fewer performance attributes.

15W-40 is commonly used in heavy-duty diesel engines, such as those in large trucks, generators, and heavy equipment. It provides excellent wear protection, extends engine life and resists oil thickening, making it suitable for use in harsh environments and under heavy loads.

Comparison between 5W-40 and 15W-40

Now that we understand the characteristics of both synthetic and mineral-based oils, let’s compare the two.

1. Viscosity: Both oils have the same hot viscosity, 40. The difference lies in cold viscosity, where 5W-40 is thinner and flows faster than 15W-40 at low temperatures. This means that 5W-40 flows more easily through the engine in cold weather, providing protection right from the start.

2. Temperature range: Synthetic oils like 5W-40 can withstand more extreme temperatures than mineral oils. They offer better performance in both extremely cold and hot temperatures.

3. Additive package: Synthetic oils have better additive packages than mineral oils, providing better detergency, anti-wear properties, and reduced friction. They also have lower volatility, which means fewer emissions and better fuel economy.

4. Engine compatibility: 15W-40 is suited for use in heavy-duty diesel engines and is commonly used in industrial applications. 5W-40 can be used in both gas and diesel-powered vehicles and is generally better suited for newer engines.

5. Price: Mineral oils like 15W-40 are less expensive than synthetic oils like 5W-40. However, synthetic oils have a longer lifespan and a better performance package, meaning they may be a better value overall.

Which oil is right for you?

Ultimately, the choice of oil will depend on your individual vehicle and driving conditions. Here are some scenarios where one oil may be a better choice than the other:

• If you have a newer vehicle, 5W-40 might be the better choice as it has a better additive package and improved fuel economy.

• If you live in a region with extreme temperatures, 5W-40 is a better choice as it provides better protection in both cold and hot temperatures.

• If your vehicle is older or does not require synthetic oil, 15W-40 is a suitable choice.

• If you have a heavy-duty diesel engine, 15W-40 is the better option.


Q. Can I switch between 5W-40 and 15W-40?

A. Yes, you can switch between the two. However, keep in mind that the performance characteristics of each oil may differ, so check your owner’s manual to determine which oil grade is recommended for your vehicle.

Q. Can I mix 5W-40 and 15W-40?

A. Although it is not recommended, there is no harm in mixing the two oils. However, it won’t provide any benefits either, and you should ideally stick to one type of oil for optimal performance.

Q. Can I use 5W-40 on an older engine?

A. While synthetic oils like 5W-40 are better suited for newer engines, they can be used in older engines as well. However, it is essential to check your owner’s manual to ensure that the oil meets the engine requirements.

In conclusion, the choice between 5W-40 and 15W-40 depends on the engine’s specific requirements, environmental conditions, and user preferences. However, it is important to note that synthetic oils tend to outperform mineral oils in almost all aspects, making 5W-40 the more recommended choice for most vehicles. Always consult your owner’s manual, follow the manufacturer’s recommendations, and stick to an oil change schedule to keep your engine running smoothly.