15W40 Vs 5W40 Diesel

15W40 Vs 5W40 Diesel: Which One Is the Better Option?

As a diesel truck owner, one of the most crucial tasks is to keep your engine in excellent condition. Choosing the right kind of oil is one of the most critical factors that affect the performance and lifespan of your vehicle’s engine. When it comes to diesel oils, the most common types are 15W40 and 5W40. But have you ever wondered which one is the best for your diesel engine? In this article, we’ll discuss the differences between 15W40 and 5W40 diesel oils and find out which one is the better option.

What does 15W40 mean?

The first number in 15W40 represents the viscosity of the oil at low temperatures. In this case, the “15” indicates that the oil is appropriate for cold weather condition, and it will not solidify or clog in a diesel engine during winter. The second number, “40,” is the viscosity of the oil at higher temperatures, which represents how well it can withstand high engine heat without evaporating or thinning down.

What does 5W40 mean?

The “5” in 5W40 represents the oil’s viscosity in cold conditions. 5W40 is thin, which makes it easy to circulate through the engine even at low temperatures. This oil will offer quick lubrication to the engine, reducing wear and tear. The “40” represents the oil’s viscosity at higher temperatures, which indicates how well it can handle high engine temperatures. 5W40 is a multitasking oil that can deliver quick and efficient lubrication, even in cold weather.

What is the difference between 15W40 and 5W40?

1. Viscosity

The primary difference between 15W40 and 5W40 is their viscosity. 5W40 is thinner than 15W40 because of the low viscosity index of the base oil, which means it can flow more quickly through the engine. In contrast, 15W40 is heavy and thick because of the viscosity index of the base oil, which makes it suitable for very high-temperature applications.

2. Engine suitability

The choice of oil depends on the engine design and its operating conditions. 15W40 is suitable for older engine designs and heavy-duty diesel engines that need high viscosity oil to operate correctly. On the other hand, 5W40 is designed for modern diesel engines that require thinner oil to circulate quickly and reduce engine wear.

3. Operating conditions

If you live in a region with a cold climate, you will benefit from using 5W40 because it is more effective in cold temperatures. 15W40 is more suitable for regions with high temperatures and tropical climates because it can withstand the heat better than 5W40. 15W40 is also used by truckers that drive long distances through different climates and terrains because it can withstand the temperature and engine wear for an extended period.

4. Fuel efficiency

5W40 has lower viscosity than 15W40, which makes it more fuel-efficient. It flows quickly through the engine, reducing friction and increasing the engine’s fuel efficiency. 15W40 is thicker, and it causes more resistance, which increases fuel consumption.

5. Environmental impact

5W40 has low viscosity, which makes it eco-friendly because it produces fewer emissions. It is also easier to dispose of because it is not as thick as 15W40. 15W40, on the other hand, produces more emissions because it is thicker, and it is challenging to dispose of.


Now that you’ve learned the differences between 15W40 and 5W40 diesel oils, you are in a better position to make an informed decision about which oil to use in your diesel engine. The choice you make depends on your engine requirements, operating conditions, and you prefer fuel efficiency, environmental impact, or engine lifespan. In summary, if you live in colder regions, have modern diesel engines, prefer fuel efficiency, and environmentally friendly products, 5W40 may be the better option. If you have older engines, drive through different terrains and climates for an extended period, and prioritize your engines’ lifespan over fuel efficiency, 15W40 may be the best option. Appropriate use of these oils guarantees smooth operation of your diesel engine, better fuel efficiency, and prolongs the engine’s lifespan.

Keywords: 15W40, 5W40, Diesel, Viscosity, Engine suitability, Operating conditions, Fuel efficiency, Environmental impact.