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10w40 vs 15w50 Motorcycle Engine Oil: The Main Differences

Engine oil is the lifeblood of a motorcycle to fight against its biggest enemy: friction. Without it, an engine would get extremely hot, and its moving parts would wear out faster. But you need to use the right oil, so you may wonder what the differences are between 10w40 and 15w50 motorcycle oil.

The key difference between 10w40 oil and 15w50 motorcycle oil is that 10w40 oil is less viscous at higher temperatures than 15w50 oil. This means 15w50 oil will generally perform better under higher temperatures, which are likely to result from an engine running at high rpm. 

Changing your motorcycle oil regularly is probably the single most important task that needs to be performed in order to keep the bike running smoothly. Below, we examine different grades of oil to find out which one is best for your bike.

Motorcycle Oil Grades Explained

All motorcycle oils are graded using an oil grading system, such as 5w40, 10w40, 15w50, and so on. Let’s simplify this by only looking at the numbers, as the W simply stands for winter. The number before the W is the lowest temperature at which the oil retains its viscosity, and the number after the W is the highest temperature that the oil can be used at.

The most fundamental property of oil is its viscosity, which is measured by a viscosity index. Basically, the viscosity index measures the change in how the oil flows as temperature changes. If the viscosity is too high, the oil may not flow properly resulting in higher friction and greater wear and tear. If the oil flows too easily, then it may not be lubricating moving parts correctly. 

The 3 Types Of Motorcycle Engine Oil 

1. Mineral Oil

Mineral oil is made from crude oil and then refined in a factory by various processes where additives are mixed with it to improve its viscosity. The big advantage that mineral oil has is its cost, because it is the cheapest of all 3. The disadvantage is that it does not provide the same degree of lubrication and needs to be changed more often.

Due to the nature of its processing, mineral oil contains a few naturally occurring impurities in very small quantities. This oil is ideal for engines below 250cc that do not generate exceptionally high engine temperatures. Mineral oil should never be used for large engines above 500cc as they run better with synthetic oil.

2. Semi-Synthetic Oil

Semi-synthetic or blended oil is a mixture of mineral oil and synthetic oil to enhance certain properties of the mix. This oil is more expensive than mineral oil. The addition of synthetic oil improves its viscosity and temperature oxidation resistance and it has a low tendency to form deposits.

Blended oil is a step above mineral oil and can be used by small-engined motorcycles that run at high rpm. The advantages are that it provides superior lubrication and lasts longer than conventional mineral oil. Although it is of higher quality than mineral oil, it should not be used in place of synthetic oil as it does not possess the same lubricative qualities.

3. Synthetic Oil

Synthetic oil is the most expensive oil of the 3, and it is made entirely in a laboratory. It has superior lubricative properties and lasts much longer than mineral or semi-synthetic oil. This oil is ideally suited for high-performance motorcycles and can withstand much higher temperatures compared to blended oil.

Using synthetic oil on motorcycles below 250cc is a waste of money, as blended or mineral oil will usually be good enough. Synthetic oil provides the best lubricative properties of all 3 oils, therefore protecting the engine the most. Since these oils are artificial, they are designed to have long life along with the best lubricative properties. Of all 3 oils, synthetic oil has the highest purity.

Why You Need To Use The Right Grade Of Motorcycle Oil

Using the right grade of motorcycle oil is vital for your motorcycle’s health as it lubricates the moving parts inside your engine and gearbox so that the motorcycle stays in good condition. If the oil you are using is too thick, you run the risk of reduced engine performance with increased wear and overheating. You’ll usually find the manufacturer’s oil recommendation in your motorcycle’s manual.

If the grade of oil that you are using is too thin, then its lubrication may not be sufficient for the engine to churn out its optimal power. Another big factor that affects your choice of grade of oil is the temperature. If you live in a city where the winter temperature is very low, this will affect your choice of oil grade, as the oil viscosity changes with temperature.

In summer as the heat rises, you need to use the correct grade of oil that can take the heat, and keep your motorcycle lubricated without burning up. As always, your best option is to consult your bike’s service manual for the correct grade of oil to be used. 

Not using the right grade of oil as specified in your manual can result in overheating, improper lubrication, and transmission problems, which could mean more frequent replacement of moving parts, adding unnecessary costs. 

The Differences Between 10w40 & 15w50 Motorcycle Oil

10w40 grade motorcycle oil will hold its performance right up to 40 degrees Celsius (104 degrees Fahrenheit), while the 15w50 grade motorcycle oil will hold its performance up to 50 degrees Celsius (122 degrees Fahrenheit). 

The number before the W tells you how the oil will flow in cold conditions. 10w40 grade oil is best used at lower temperatures, while 15w50 oil should be used at higher temperatures.

Is 10w40 Oil Good For Your Motorcycle?

10w40 oil is good for most motorcycles, in particular smaller ones that don’t rev very high. You need to consider the ambient temperature and the type of motorcycle. A motorcycle running at high rpm needs better lubrication than a bike running at low rpm, making 10w50 oil a better choice. 

When using your bike in summer, the preferable grade of oil to use is the one that can withstand the higher engine temperature added to the ambient temperature of the season. For cold winters, the correct oil to choose is the one that flows best in your motorcycle.  

Is 15w50 Oil Good For Your Motorcycle?

15w50 oil is best used for motorcycles with engines that run at high rpm and generate more heat. At the same time, 15w50 oil can be used in winter as well because of its low-temperature viscosity. Motorcycles with smaller engines do not generate as much heat, and can typically use 10w40 oil. 

There are exceptions to this, as a few small-engined motorcycles run at high rpm necessitating the use of 10W50 oil. In the heat of summer, motorcycle engine temperatures can go much higher than expected, so it may be worthwhile to choose an oil grade that can lubricate the engine adequately in the summer heat.

You Can Experiment By Using Different Oil

If you are dissatisfied with the performance of both 10w40 and15w50, you can try using 10W50 instead. It all depends on the heat generated by your motorcycle engine and the seasonal temperature as well. If 10W50 isn’t good enough, 10W60 is also available although its usage is very rare. This is only for motorcycles of 500cc and above that run at high rpm.

While experimenting, keep a close watch on your engine temperature and note how the bike feels while riding it, as the oil difference will be reflected in the engine sound and smoothness of the transmission.

Final Thoughts

10w40 and 15w50 motorcycle oils vary in how viscous they are at different temperatures. Keeping your engine well-lubricated needs to be your top priority, so that it works perfectly all the time. It’s essential to use the right grade of oil at the right time of the year to get the best results.