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5w40 vs 15w40: What’s The Difference

You can’t expect a car to run smoothly unless you undertake proper maintenance. When it comes to maintenance, engine oil is an essential component to ensure your motor functions properly. However, there are many types of engine oils available in the market, which can often make it confusing for consumers to select the right option as factors such as advertising can make you choose an oil that isn’t ideal for your car engine.

You might not think it’s important to know how to choose the correct oil for your car, and in the short term, you might not see much of a difference in performance. However, in the long term, your vehicle can end up with some problematic issues, such as engine damage.

In this article, we will be taking a closer look at 5w40 and 15w40 to determine which is the best solution for your engine.

The Differences Between 5w40 and 15w40

Temperature Range

The name and numbering of the two oils indicate that they can be used throughout the year, as long as the temperatures don’t surpass their range. The key distinction between 15w40 and 5w40 engine oils is mostly related to how effectively these two enable the engine to regulate its temperature to ensure optimum combustion and performance.

15w40 is suitable for temperatures between -20 degrees C or -4 degrees F and +40 degrees C or 104 degrees F, whereas 5w40 is suitable for temperatures between -30 degrees C or -22 degrees F and +40 degrees C or 104 degrees F.

As a result, we can infer that 15w40 is better suited for engines operating in hotter climates while 5w40 is more efficient in colder climates.


The viscosity of an oil refers to how it flows. As a rule of thumb, when temperatures increase, the viscosity decreases as the oil begins to take a more liquid consistency which flows more easily than it did at a lower temperature. However, the oil must be used between certain specified temperature ranges to ensure it works efficiently, which is why engine oils come with oil viscosity grades to inform the consumers about whether they’ll be effective for their vehicles in certain temperatures.

The original equipment manufacturer (OEM) typically suggests viscosity grade(s) according to the type and life of the engine, and they should be followed by the car owners as using the wrong oil can make the warranty null and void.  The appropriate viscosity grades are based on the probable ambient temperatures, especially the temperature of the engine during start up.

Because the working temperature of engine oil does not fluctuate much with ambient temperature, the oil with the suggested viscosity can be used for different applications.  The viscosity grade is determined by the numbers preceding the “W,” which refers to the minimum engine starting temperature and determines the lubricant’s fluidity, flowability, and effectiveness.

Lubricants with a 5W viscosity grade have a better flow at lower temperatures than those with a 15W viscosity grade, which makes them suitable for being used for lower engine starting temperatures. As the 5w40 has a greater temperature range than the 15w40, it maintains its viscosity at much lower temperatures, whereas the 15w40 can become troublesome if your engine tends to run hot either due to aggressive driving techniques or extreme weather conditions.

It is important to ensure you get engine oil with the right viscosity as if you live in an area where the temperature falls below the viscosity grade, you might not be able to start your engine, and even if it does, there is no guarantee that the take care the oil will suitably coat the engine’s moving parts, which can lead to friction, overheating, and even engine damage.

Engine Protection

Another significant benefit of motor oil is that it protects the engine from wear and tear. While 5w40 has a greater range of functionality when it comes to temperature, it is not necessarily the motor oil of choice when it comes to protecting your engine from any damage.

On the other hand, the 15w40 is commonly used in engines that have been working for a while, especially if they have passed the 60.000 miles benchmark since it preserves the engine better than 5w40 due to its viscosity and the way manufacturers build the motor and how it interacts with the oil.

Oil Change Frequency

Engine oil also needs to be changed to ensure your engine is working to its maximum potential. The engine oil replacement time and travel for the 5w40 is 9000 miles or 15,000 kilometers, whereas the oil change frequency of 15w40 should be less than 3000 miles or 5000 kilometers. As the 5w40 oil needs to be changed less frequently, it can keep your engine running smoothly for a longer period of time while also providing a larger operating range of temperature, unlike the 15w40, despite it being better suited for worn-out engines due to its enhanced protection ability.

The 15w40 is also more economical when it comes to fuel consumption in the engine compared to the 5w40.

Final Thoughts

Selecting an oil can be a difficult decision, which is why the first thing you should do is refer to your car manufacturer’s handbook or contact them to check if they have a recommended option. However, if there are no guidelines available to you, you need to consider the temperature of the area you live in, your driving style, the miles on your engine, and the viscosity of the oil to ensure you reach the right decision.