Updated at: 03-08-2022 - By: Lucas

A car’s engine is one of its most important components. A car isn’t a car if it doesn’t have an engine. In order to continue providing its role, extreme caution is required.

That’s why it’s important to know which oils to use and which ones to avoid when it comes to your car’s engine. There are a variety of factors to consider when deciding which oil is ideal for you.

Temperature range, among other things, are included in the list of factors that affect the oil’s kinematic viscosity index. 15w40 and 20w40 are two of the oils you may want to explore. Do you want to discover which of these two oils is better for your engine? Checkout

15w40 engine oil

15w40 engine oil

The SAE designation for engine oil is 15W-40. The viscosity grade, working temperature, and other information is provided in this SAE.

15W40 engine oils are multigrade oils with outstanding flow qualities in both hot and cold conditions. This implies that the essential oil lubrication sites are supplied optimally at both high and low temperatures..

The oil’s flowability at zero degrees Celsius is 15 W. Oil can still be pumped even at a temperature of 25 degrees celsius, which is equal to about 13 degrees Fahrenheit. Temperatures above 100 degrees Fahrenheit are indicated by the number 40.

At 100 degrees Celsius, this oil’s viscosity ranges from 12.5 to 16.2 square millimeters per second.

Viscosity index

In terms of viscosity, the oil has a 135.

Temperature range

The oil’s operating temperature range is 25-40 degrees Celsius, or 13-104 degrees Fahrenheit. As a result, it works well in both cold and hot environments.


The oil has an API of Ci 4 Grade. “

20w40 engine oil properties

20w40 engine oil

In hot temperatures, this oil’s SAE rating of 20w40 indicates that it meets the temperature criteria for 20 weight and 40 weight. These oils are 20W in cold weather, and 40 in hot weather, and the viscosity or weight of each is determined by the temperature.

Viscosity index

The minimum viscosity index is 98.

Temperature range

22 degrees Fahrenheit to 122 degrees Fahrenheit, or 30 degrees Celsius to 50 degrees Celsius, is the temperature range for this oil.


Ch 4 is the API metric for SAE 20W40 engine oil.

ACEA properties

An A3, a B3, and an E2.

Differences between 15w40 vs. 20w40

  • 20w 40 oil is thicker than the 15w40 oil; therefore best for use in older cars.

  • Since 15w40 is thinner, it is easier to start in colder conditions.

  • 15w 40 has a higher flowability


  • They both offer good quality lubrication for engines in hotter conditions

  • They both protect against corrosion and wear.

Advantages of 15w40 oil

Diesel engines benefit greatly from the 15w40 heavy-duty diesel engine oil. By improving protection against corrosion and wear, this oil improves engine performance in both old and new engines.

The use of 15w40 engine oil reduces sludge and varnish formation since it is extremely anti-oxidative and has a high degree of thermal stability.

The warranty duration of a gasoline or diesel engine can be extended by using 15w40 engine oil in cases when the sulfur content of the fuel exceeds 500ppm and the engine is more than ten years old.

Many types of engines benefit from this oil, including those in big trucks, farm tractors, light trucks, passenger cars, and off-highway diesel equipment, among others.

Disadvantages using 15w40 oil

In hot climates, 15w40 engine oil is the best choice. A 15w40 in a cold atmosphere reduces the horsepower of an engine.

What benefits and disadvantages do 20w40 have?

For engines operating at different temperatures, the multi-grade oil, 20w40, is advantageous. This oil involves two different oil grades, mono, and multi grade oil.

The use of monograde oil is appropriate when the engine is running at a specified flow rate, such as when the engine is cold or heated. Multi-grade oil is ideal for engines with two distinct flow rates, such as those that operate at room temperature and those that operate at cold start. using 20w40 improves

  • High terminal stability

  • Extended interval draining

  • Excellent clutch friction performance

  • Anti-wear properties

  • Increased cleaning capacity

Disadvantages of 20w40 to both new and old engines

In colder climates, 20w40 engine oil should not be used.

Can you mix 15w40 and 20w40?

No, 15w40 and 20w40 engine oil should not be mixed. There are some differences between these two oils. When it comes to temperature, 20w40 works best between 20°C and 40°C, whereas 15w40 works best below 20°C. When these oils are blended, their viscosity variances will lead to engine inconsistency.


Despite the fact that both oils are necessary, 20w40 is best for older engines. High viscosity is the reason why. As a result, the ancient engines are spared more wear and tear. The high viscosity of 20w40 makes it ideal for use in hotter engines.

15w40 is the best choice for new engines because of its low viscosity and use in cooler climates.