10W50 vs 10W40: Fuel efficiency, Viscosity & High Temperature

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Last Updated on 4 months by Ollie Barker

10W50 vs 10W40

To reduce friction and wear and tear caused by the moving parts of the car, motor oil is used to lubricate the engine components. Of course, in order to protect a powerful engine, the oil grade needs to be greater.
There are several sorts of oil based on varying grade and viscosity. Today, I’ll outline the differences between 10w50 vs 10w40 in this article.

What Distinguishes 10W40 Engine Oil From 10W50 Engine Oil?

Because oil is a lubricant, it helps moving parts move more readily by reducing friction between them. By doing this, you can stop the engine from deteriorating and from overheating or cooling.
Because it provides a good blend of low-temperature flow, high-temperature protection, shear stability, and chemical stability for long-life performance under challenging conditions, a typical modern engine will use a 10w-40 or a 10w-50 oil.

When oil is cold, the greater the “W” number, the thinner the oil is. The thickness at low temperatures increases with decreasing number. Engine oil typically has an SAE grade of 5W-20 or 5W-30.

According to your engine. As long as the engine is still functioning within the normal operating temperature range, using a lesser weight (thinner) of oil will not cause any harm if you use a greater oil weight since your engine was built for it.

Using 10W50 oil for:

There is no danger in using it if you have a vintage car (or any engine that uses 5W-30 or 10W-30 oil) that needs a 10W-50 grade.

The heavy viscosity of 10W-50 won’t harm anything since these engines are made to run with thinner oil. The thicker oil won’t offer any additional protection until the engine requires higher temperatures than usual; thus there is also no benefit.

Using 10W40 oil for:

Engines with lesser horsepower requirements and need oil that flows effectively at lower temperatures often utilize 10w-40. These engines, which normally produce 175 horsepower or fewer, are present in most cars today.

10W50 vs 10W40

Let’s concentrate on the distinctions between the two. On the basis of fuel efficiency, viscosity, and hot weather, we shall distinguish between them.

Fuel efficiency

The 10w40 motor oil is designed for engines with low horsepower requirements, and it is typically used in vehicles with lower output. However, since the introduction of 0w20 and 5w20 motor oils, fuel economy motor lubricants have gained popularity.

Many of these motor oils will boost fuel economy by at least one to two percent. You only need to know that lighter oils will provide you with greater gas mileage because of their low viscosity, making them easier to transfer through the oil system.


The viscosity of 10w40 and 10w50 oils is the same at absolute zero. They are recognized as belonging to the same class. The 10w50 motor oil will have a higher viscosity than the 10w40 motor oil when operating at 100 degrees Celsius.

The viscosity index for both the 10w40 and 10w50 motor oils is one hundred sixty and one hundred sixty-seven for the latter. As a result, the viscosity of 10w50 motor oil will vary more subtly over the temperature range. As a result, both oils will function similarly at low temperatures.

However, at operating temperatures, 10w50 motor oil will provide higher protection than 10w40 motor oil. Additionally, due to its high viscosity, the 10w50 motor oil will require more effort to pump than the 10w40 motor oil.

High temperature

The engine oil will be thinner when cold if the W number on it is higher. And the thicker it will be in cold temperatures, the lower the number.

The ability of the motor oils to become thin in hot temperatures is what distinguishes 10w40 motor oil from 10w50 motor oil. While the temperature of the 10w40 motor oil rises, the 20w50 motor oil will not thin as quickly, but it may become overly thick when operating in low temperatures.

Can I Substitute 10W50 for 10W40?

Yes, you can, but you must still follow the advice provided in your owner’s manual. For instance, a modern car’s engine, which needs a 10w40 oil, won’t benefit from the extra protection provided by a 10w50 motor oil.

In that case, you must consistently follow the manufacturer’s advice for your car. Using an oil that is not advised by your vehicle’s manufacturer can hasten the onset of problems.

Which Oil, 10W50 or 10W40, Is Better?

The viscosity of 10w50 and 10w40 motor oils is the same at absolute zero. The viscosity of the 10w50 motor oil will be higher than the 10w40 motor oil at operating temperature, even if both of these motor oils are in the same class and are not claimed to be equal.


The viscosity index of oil indicates how thick or thin it is at various temperatures. When it gets cold, an oil with a higher viscosity index will be thinner than one with a lower viscosity index and won’t flow as well. You should frequently check it for your particular engine.