15W40 VS 20W50 – Which Engine Oil is Better???

When it comes to choosing the right engine oil for your needs, it is best to keep in mind that viscosity is very important. Viscosity actually plays a role in telling its lubrication in regard to both low and high temperatures. Since there are many options available, it is essential that you know the exact requirements for your car.

Let’s say for example, 15W40 is said to have a low and high-temperature viscosity of 15 and 40, while on the other hand, 20W50 has a viscosity of 20 and 50, which shows the consistency of the 20W50 oil. Because of the thickness of these oils, they are great for hot temperatures.

The fact that there are so many things to keep in mind when looking for the right oil for your vehicle, it can be a bit challenging. But, it’s safe to say that we are here to help you out in making the right decision. In this article, we are going to compare the 15W40 and 20W50 engine oils just to ease your mind.

What is 15W40 Oil?

15W40 VS 20W50

There is no doubt that 15W40 is very well known to be one of the best engine oil for fleet cars. Apart from that, it is said to be a great choice for buses and trucks that run on CNG or LNG. This high-quality motor oil is made of base oils and special additives.

There is no doubt that the ash formulation components of this oil type are what cause it to be nitration, thermal, and oxidative stability. What this means is that it reduces the ash that accumulates in the combustion chamber. Not only that, but this oil helps to protect against sludge and other contaminants.

This makes it the right choice for high-performance engines. This oil meets all industry standards, as fleet cars need the right performance as this will prevent any type of failure from happening.

We also appreciate the fact that this oil plays a role in protecting the cylinder liner and bearing from being damaged. Apart from that, it helps to keep corrosion, rust, dirt, and sludge away from engine components. It is also considered to contain phosphorus and zinc.

Pros of Using the 15W40 Engine Oil

What we love about this engine oil is that it has lots of benefits, especially diesel engine oils. It can reduce the heat, making the car use less gas, and even plays a role in reducing pollution. It even offers shear stability that helps to reduce consumption, which allows it to last a lot longer.

Cons of Using the 15W40 Engine Oil

Several cons come with this engine oil. It does a wonderful job during the winter times, but it tends to have a greater risk of shear during the summer heat. Upon using this oil your engine has a higher chance of experiencing wear and tear over time.

How Does 15W40 Affect An Engine?

We definitely find that the 15W40 oil is very beneficial for most engine types due to the fact that it reduces the amount of heat that is being generated by the engine. Not only that, but it has a greater chance of lowering emissions while increasing efficiency. The only issue is that the 15W40 may result in the engine parts being worn over time especially if you don’t change oils on time.

What is 20W50 Oil?

20W50 Oil

The 20W50 is also said to be a great performance motor oil that is known to do a superb job. While you will find that the 15W40 is more fuel efficient, the 20W50 is considered to work for almost all vehicles and it also protects against wear and tear while ensuring that the engine is cleaned.

This motor oil does a great job of reducing deposit formation. The engine’s anti-wear features help it to protect all parts of the engine. Apart from that, this oil will make sure the car can easily be started in cold weather and keep its performance stable even in hot weather.

Another thing to know is that this oil can be used for heavy-duty vehicles. LPG and CNG-powered vehicles are the most suitable. It is also safe to say that it can even work in engines that require API SL quality engine oil.

Pros of Using the 20W50 Engine Oil

Some amazing advantages come with using the 20W50 such as reducing engine heating and increase efficiency while also reducing air pollutants. Another thing we find interesting is that it works well for old engines and can help you get the most mileage out of your car.

Cons of Using the 20W50 Engine Oil

A disadvantage that comes with 20W50 is that it is thicker so if it is a case where you decide to use it as a replacement for 15W40, then it will increase friction which will result in fuel and power loss.

How Does 20W50 Affect An Engine?

One thing for sure is that using the 20W50 will allow your engine to last longer than if you were using the 15W40. When you are in cold weather, you can expect the 15W40 to flow much better and the reason for this is that it has less dense than the 20W50 oil.

What is the Difference Between 15W40 and 20W50?

  • It is very well known that oil with a viscosity of 15W40 is usually used in diesel engines, while oil that has 20W50 is normally used in gasoline-powered cars.
  • It has been reported that the 15W40 has a specific gravity of 0.875 while the 20W50 has 0.88.
  • When you compared both oils, the 15W40 comes equipped with a viscosity index of 143, while the 20W50 has a viscosity index of 141.
  • You will certainly notice amazing performance from 15W40 at low temperatures, while the 20W50 is known to do a superb job at high temperatures.

Similarities Between 15W40 and 20W50

  • It’s safe to say that both oils are known to be interchangeable and are said to have similar levels of efficiency
  • Both oils are considered to be heavy-duty motor oils and this is due to their viscosity, which allows them to be in that category
  • Both oils do a superb job of preventing the formation of harsh deposits and sludge buildup.

15W40 vs 20W50 – Which Engine Oil is Better?

When it comes to cold weather, we strongly believe that the 15W40 would be the better option, while 20W50 is the more effective oil for hot temperatures. In terms of short trips, the 15W40 would be the one to use, while the 20W50 is the better oil if you are planning on going on longer trips as this would cause the engine to run hotter.

We think that the 15W40 is the right choice for fleet cars. Not only that, but it is great for vehicles with compressed natural gas or liquefied natural gas engines.

The 20W50 is considered to be a great high-performance motor oil. Though you will find that 20W40 is the better oil for gas mileage, the 20W50 is widely recommended since it protects the engine and helps to keep it clean at all times.

So, if it is a case where your engine is brand new and uses 15W40, then you should use it, but if it has 300,000 miles on it, and needs 15W40, we think it would be best to go with 20W50 since the thicker lubricant will be better attached to your bearings and other moving parts and reduce wear and tear.

FAQs – Frequently Asked Questions

Q. Can I Mix 20W50 With 15W40?

Yes, you can do so, but the only thing that will happen is that the oil is a little thicker. But, we don’t think it would be a good idea to mix both oils. Even if both oil viscosity is the same, we don’t recommend mixing them.

Q. When Should I Use 20W50 Oil?

This motor oil is the best option for older vehicles or where the temperature is extremely high. Apart from that, this oil help to keep your vehicle clean from sludge and plays a role in extending the life of your engine.

Q. Can I Use 20W50 In My Diesel Engine?

We think the 20W50 is ideal for large diesel and gasoline engines, high-performance motorcycles, and aircraft. It is also considered to be a superb racing oil for high temperatures and the reason for this is that it doesn’t thin out when it gets hot.


In this article, we have compared the 15W40 and 20W50 motor oils. At this point, all you have to do is carefully read and choose the one that best suits your needs. The price point of the 15W40 and 20W50 engine oils is another thing you may want to keep in mind when picking. The good news is that both oils are interchangeable and have similar levels of effectiveness.