It’s important to know what kind of oil your car’s engine needs. Motor oil is an essential part of your engine. Putting oil in your engine makes it run better and keeps it from breaking down in the future.

The thicker oil takes longer to get into the engine than oil that is thinner. As the temperature goes up, oil becomes less thick. Because of this, the motor oil will end up being thicker. If you add these to base oils, they will act like thin oil. So, in this post, we’ll talk about how 5w40 and 15w40 motor oils are different.

What is 5w40 Engine Oil?

It runs on a 5w40 motor. Naturally-occurring oil is one sort of motor engine oil. The name “5w40 engine Oil” refers to the oil’s ability to adapt to the needs of the vehicle’s engine to achieve its intended aim. This shows that the name is inserted with a specification for starting the defined process of lubricating the engine. In addition, it indicates that this procedure is available.

The mark “5w,” which stands for “winter,” represents the requirement that the oil has a predetermined maximum viscosity or flow at low temperatures. Oil viscosity at 0 degrees Celsius is represented by 5; w symbolizes winter, and 40 depicts oil viscosity at 100 degrees Celsius.

Viscous oil is required for this engine type since the oil can’t be too watery and still move freely through the engine. As a result, the engine must use an oil that fits these conditions to fulfill its purpose. When it’s cold outside, the oil will be most effective.

What is 15w40 Engine Oil?

The 15w40 designation for engine oil refers to one perspective. As a result of its 15w40 designation, the oil implies that it is a multigrade product obtained from minerals (CARBIBLES, 2019). Many of the oil’s features are defined by its name, which is a combination of letters, numbers, and both.

Fifteen degrees centigrade and 40 centistokes refer to the viscosity in centistokes that must be applied for this to work. Multigrade oils are popular because they can endure both the cold of winter and summer heat, making them ideal for a wide range of applications.

Performance additives in the engine oil are designed to give the vehicle a high-performance system within its engine. According to the viscosity index, if the temperature is low, the oil’s viscosity is the same as that of SAE 15Woil. The 15W40 multigrade motor oil can be used in gasoline and diesel-powered vehicles.

Differences Between 5w40 and 15w40?

Differences Between 5w40 and 15w40


For example, oil with an SAE viscosity grade of 5w40 will flow like a 5w oil at low temperatures and a 40w oil at high ones.

As a result, the viscosity grades of 5w40 engine oil and 15w40 engine oil are the same while the engine is running at the same temperature. A lower viscosity grade is associated with the thinned substance.

Savings on Energy Consumption

The fuel economy will be determined by its usage and supply in the market. For example, 5w40 motor oils are not always accessible on the market. The 15w40 motor oil, on the contrary, is commonly utilized because it is a multigrade product.

You can save money by using the 15w40 motor in various engines. As a result, it has a monopoly on the economy. Unfortunately, there isn’t enough information available to compare the fuel economy of the two.

Heat Waves

The 15w40 motor oil has a thicker viscosity than 75% of its weight. Because the polymer thickens to forty pounds, this is the reason. Temperatures above 70 degrees Fahrenheit will cause the 5w40 motor oil to thicken into a forty-weight oil.

Contrary to popular belief, this frequently has the opposite effect. For example, the consensus is that heating motor oil causes it to thin out. Generally, yes, but there’s always the matter of polymers.

The season of winter is symbolized by the letter w. If it’s cold, the oil’s flow rate will plummet. The oil will be thin if the number is low.

The local climate and surroundings influence engine oil selection. The weather has a significant impact on the type of motor oil that should be used in a car’s engine. So that conflicting events do not develop and result in engine efficiency issues, it enforces a form in the most optimal way possible.

On the other hand, the weather should be adjusted in specific ways to consider the efficiency of the engine and the flow of oil. To properly connect the engine’s operation to the local weather and climate, it is essential to consider the weather when fueling the vehicle.

Product Table: 

Products Features

Mobil 1 122094 5W-40 Formula M Motor Oil – 1 Quart Bottle 6 Pack
This is the best oil to meet the MB-AMG 229.5 specification. It’s easy to get your oil changed “on time” thanks to the low price and fast delivery of this product.
Mobil Super 96819 15W-40 Delvac 1300 Motor Oil – 1 Gallon (Pack of 4)Crafted to provide trouble-free, reliable service and suitable for your automobile and way of life. They are produced to exacting standards of excellence or better.
Liqui Moly 2332 Leichtlauf High Tech 5W-40 Engine Oil – 5 LiterHigh lubrication reliability at all temperatures, even at low temperatures. This oil has a long service life because of its strong wear resistance and compatibility with commercial engine oils.
Liqui Moly 20232 Molygen New Generation 5W40 Motor Oil, 5 l, 1 PackLow viscosity and strong shear stability ensure that the motor oil does not create deposits. As a result, the engine uses less fuel and lasts longer. An all-season, high-performance oil with reduced friction.
Castrol EDGE 5W-40 A3/B4 Advanced Full Synthetic Motor Oil, 1 Quart, 6 PackCastrol EDGE Euro Car fluids are made with Fluid TITANIUM Technology to prevent oil breakdown and friction, which transforms under pressure to increase film strength.
These fluids have also been optimized to deliver up to 40% better performance* against ACEA standards, unlocking maximum engine performance.
Castrol Vecton 15W-40 CK-4 Part Synthetic Diesel Engine Oil, 1 Gallon Jug (Pack of 3)The 45 percent extra performance reserve of SYSTEM PRO TECHNOLOGY helps stop oxidation, reduce deposits, and neutralize dangerous acids, among other things. You can be more sure of figuring out your maximum drain interval because of its higher temperature handling power.
Valvoline Premium Blue Extreme SAE 5W-40 Full Synthetic Diesel Engine Oil 1 GA, Case of 3In cold conditions, superior synthetic base stocks allow faster, safer start-ups and improved thermal characteristics. Heavy-duty engines benefit from lengthy oil life because of exceptional oxidation resistance.
Valvoline Premium Blue SAE 15W-40 Diesel Engine Oil 1 GA, Case of 3High levels of shear stability ensure that parts remain in grade. Outstanding protection against wear in comparison to industry standards.
Royal Purple 06540 API-Licensed SAE 5W-40 High-Performance Synthetic Motor Oil, 1 Quart (Pack of 6)Protection against LSPI has been increased reducing greenhouse gas emissions. Enhanced safeguards for automobile exhaust emissions systems.
Royal Purple 04154 / 300905 Duralec Super 15W40 CK-4 Motor Oil Synthetic – 1 gal. (Case of 3)Efficiency in the use of fuel.Improved security for the high-priced catalytic system.
Shell Rotella T6 Full Synthetic 5W-40 Diesel Engine Oil (1-Gallon, Case of 3)A wide range of heavy-duty engine applications benefits from exceptional wear prevention, from pickup trucks to tractors to semi rigs.1.5 percent better fuel economy without sacrificing engine safety or durability (compared to 15W-40 oils).
Shell Rotella T6 Full Synthetic 15W-40 Diesel Engine Oil (1-Gallon, Case of 3)Pumpability at low temperatures to reach crucial engine sections more quickly. Efficiently designed case with three 1-gallon bottles for simple pouring.

FAQs about 5w40 vs 15w40

Which oil is better, 5w40 or 15w40?

When choosing the best oil for your car, think about what the manufacturer recommends. This is a fundamental rule that everyone needs to follow. The warranty on your car will also depend on this.

Also, you should know that the weather has a significant effect on what kind of motor oil is best for your engine. It is better to use 5w40 motor oil in a cold climate instead of 15w40 motor oil because 5w40 oil is better at cold starts and is quieter than 15w40. 

When should you switch from 5w40 to 15w40 if you’re using 5w40?

Your choice between 5w40 and 15w40 motor oil will depend on how cold your winters are. When starting your engine when it is cold, the 5w40 oil is much better. This is because the 5w40 motor oil can flow better in these conditions.

But 5w40 motor oil has a high viscosity and can protect your engine from wear and tear when the engine is running hot. It’s also good to use 5w40 motor oil in European cars with gas engines.


In a nutshell, switching from 5w40 to 15w40 motor oil is not unusual among car owners. If possible, you should try to avoid doing that, as switching them both is an option.

To ensure safety, the best course of action is to go to the owner’s manual to find out what type of motor oil the manufacturer recommends. You can be sure that your car’s manufacturer is familiar with the best motor oil to use in this situation.