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What Is The Difference Between 15w-50 Vs. 10w-40 Engine Oil?

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Hi, I'm Azim Uddin, a student who loves cars. Visit to learn about car maintenance for beginners and experts. In my studies, I found a cool connection between hosting and car care. Join me on this journey where every road has a story, and hospitality meets the thrill of cars. Explore, learn, and enjoy the ride with me!

Last Updated on May 10, 2024 by Azim Uddin

When maintaining your motorcycle’s engine, choosing the right oil is vital. The viscosity grade of engine oil plays a crucial role in ensuring your engine’s longevity and performance. That is why most bikers debate whether to go for a 15w-50 or a 10w-40 engine oil.

So, what is the difference between 15W-50 vs. 10W-40 engine oils? A 15W-50 is a thicker oil better suited for high-performance engines in hotter climates. Conversely, a 10W-40 is more suitable for smaller engines in cold temperatures.

Continue reading to delve deeper into the specific applications, advantages, and considerations for each engine oil. You will also learn the main differences between them and which oil is right for you.

Comparison Table Between 15w-50 Vs. 10w-40 Engine Oils

Here is a table showing a summary of all the differences between these two versatile engine oils.

Cold-Weather PerformanceLess suitable for extremely cold climatesBetter equipped to handle cold starts
Hot-Temperature ProtectionIdeal for extreme heat exposureLess suitable for extreme heat
Fuel EfficiencySlightly lower fuel efficiencyEnhanced fuel efficiency
VersatilityComprehensive protection against wear, oxidation, and depositsSuitable for a variety of engines, ideal for everyday driving
PriceMore expensive, ranging from $400-$800More affordable, ranging between $250-$600
Manufacturer RecommendationsRecommended for high-performance or heavy-duty enginesRecommended for standard motorcycles in temperate climates
Comparison Table

What Is The 15w-50 Engine Oil?

15w50 engine oil

Your 15w-50 engine oil is specially designed for modern four-stroke engines. The “15w” indicates that this engine oil has a viscosity index rating of 15 when exposed to cold conditions. This simply means that even if you are in an area where it gets as cold as -25°C, this oil will still work on your motorcycle.

See also  20w40 Vs. 20w50: Which Motor Oil Should You Choose?

To remember the significance of the “W,” you can think of it as standing for winter, defining the oil’s performance in cold temperatures.

On the other end of the spectrum, the “50” in 15w-50 simply shows how this engine oil performs when it gets hot. This number is derived when you pass the oil through a viscometer at 100°C.

The figure that appears on the viscometer is the official SAE class for the oil, which, in this case, is 50. That is why the kinematic viscosity of 15W-50 engine oil falls within the range of 16.3 to 21.8 mm2/s.

What Is The 10w-40 Engine Oil?

10w40 motor engine oil sample

The “10W” in 10W-40 shows how this oil performs in cold temperatures. It specifically indicates that this engine oil possesses a viscosity index rating of 10 in cold conditions. This means that this oil can still perform well even in temperatures as cold as -30°C.

The “40” shows the engine oil’s viscosity when exposed to higher temperatures of 100°C. Basically, this is how this engine oil performs when it gets hot. That is why the kinematic viscosity of 10W-40 engine oil falls within the range of 12.5 to 16.2 mm2/s.

Differences Between 15W-50 and 10W-40 Engine Oils

15W50 vs 10W40

There are several differences between these two engine oils that set them apart from each other. These differences include the following.

1.     Cold-Weather Performance

The primary distinction between 15W-50 and 10W-40 engine oils lies in their cold-weather performance. If your engine has 15W-50 oil, it will be less suited for extremely cold climates as it has harder cold starts and slower oil flow.

See also  10W30 vs 15W40: Differences, Performance, Compatibility, and More!

In contrast, the 10w-40 is better equipped to handle cold starts. It flows more easily in low temperatures. This reduces wear on engine components when starting your motorcycle in cold environments.

2.     Hot-Temperature Protection

If you have a 15w-50 engine oil, it will maintain its viscosity well under high temperatures. This quality makes it a robust choice for engines exposed to extreme heat, such as those in high-performance or heavy-duty applications.

On the other hand, while 10W-40 does provide good hot-temperature protection, its viscosity rating strikes a balance between protection and flow. This makes it less suitable for engines that regularly operate under extreme heat.

3.     Fuel Efficiency

The 15W-50 has a slightly lower fuel efficiency compared to the 10W-40. This trade-off is due to the added protection it offers under high-stress conditions.

On the other hand, 10W-40’s moderate viscosity can enhance fuel efficiency, making it a more suitable choice for daily driving in vehicles where economizing on fuel is a concern.

4.     Versatility

The 15w-50 oil, with its thicker viscosity, has comprehensive protection against wear, oxidation, and deposits. This makes it an ideal choice for demanding conditions where heavy-duty performance is required.

In contrast, the 10w-40 adapts well to different driving conditions. You can use it in a variety of engines, both old and new. After all, it provides the necessary protection for everyday driving in standard motorcycles.

5.     Price

Typically, 15w-50 oils are more expensive than their 10w-40 counterparts. If budget constraints are a concern, you may want to factor in the cost difference when making your selection.

While 15w-50 offers excellent protection, it comes at a higher price point, ranging from $400-$800. On the other hand, 10w-40 is often more affordable, ranging between $250-$600, which makes it an attractive option if you are cost-conscious.

See also  20w40 vs 10w40: Which Viscosity is The Best for Your Engine in Winter?

6.     Manufacturer Recommendations

Vehicle manufacturers often provide specific recommendations for the type of engine oil best suited for their vehicles.

Most manufacturers will recommend the 15w-50 for high-performance or heavy-duty engines, considering its exceptional protection properties. It’s crucial to heed these guidelines to ensure optimal engine performance and longevity.

In contrast, the 10w-40 is frequently recommended for standard and smaller motorcycles operating in temperate climates. If you are an everyday rider, this engine oil will be the default choice that aligns with your manufacturer’s recommendations.

Choosing Between 15w-50 And 10w-40 Engine Oils

If you live in a region with cold winters, a 10W-40 oil is more suitable for easy cold starts. On the other hand, 15W-50 is better if you live in an area with scorching summers.

If you have a motorcycle with a bigger engine, the 15W-50 will provide the necessary protection your engine needs at higher revs. For everyday use in a standard motorcycle or one with a smaller engine, 10W-40 should be sufficient for you. This is especially true if your motorcycle isn’t above 500cc.

The frequency of oil changes also plays a role in your choice. Heavier oils like 15W-50 extend the time between changes due to their durability. Lighter oils like 10W-40 require more frequent changes for optimal performance.

Finally, if you’re on a budget, the 10w-40 is generally more affordable than the 15w-50.


Here are a few additional questions that you might be asking about these engine oils.

Q1: Are 15W-50 and 10W-40 oils interchangeable in any engine?

Both 15W-50 and 10W-40 are versatile, therefore, you can interchange them as you see fit. However, you should check your manual first to see if your motorcycle’s manufacturer recommends doing this. This will help ensure that you do not break the rules of your warranty coverage.

Q2: What’s the difference between multigrade engine oil, like 10W-40, and monograde oil, such as SAE 30?

Multigrade oils like 10w-40 have viscosity characteristics that adapt to both cold and hot temperatures, making them versatile for various climates. Monograde oils like SAE 30 have a fixed viscosity and are more suitable for specific operating conditions and older engines.


Choosing the right engine oil for your motorcycle is a decision that should not be taken lightly. Understanding the differences between 15w-50 vs. 10w-40 oils, particularly in terms of temperature viscosities, is essential for optimal engine performance and longevity.

The key factors to consider are your local climate, the type of vehicle you own, manufacturer recommendations, oil change intervals, and your budget. Make your choice wisely to help keep your engine running smoothly.

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