Updated at: 26-07-2022 - By: Lucas

A car’s engine relies heavily on engine oil. Engines will have a difficult time running if they lack oil. Your vehicle’s specific needs dictate which engine oil you should use. Even though they don’t get the credit they deserve, engine oils are a vital source of information in the automotive industry.

In addition, internal combustion would be impossible without them. To generate power, modern motor engines compress air and use only a minimal amount of fuel. Oil engineers have taken the time to investigate the qualities of many types of synthetic oils, as well as natural and naturally produced ingredients. This enables well-prepared engine oil.

There are a variety of engine oils available for purchase. There are a lot of parallels and differences between the 10W40 and the 15W50 motor oils that I’ll discuss in this article. The characteristics and functioning capacities of the various oils vary.

10w40 engine oil properties

10w40 Oil Temperature Range-4

The Society of Automotive Engineers defines 10w 40 as the weight or viscosity of engine oil. At both low and high temperatures, the oil has a viscosity rating of 10 W. This oil thickens in cold temperatures but thins when heated. After heating, the viscosity of this oil remains constant. For example, a 10W weight oil performs just as a 40W weight oil does when it’s cold and hot.

The 10W rating

The cold viscosity of oil is represented by the number 10W. Because of their high viscosity, lubricants have a limited cooling range. For Winter, thicker oil has a higher W value; W stands for “Winter”. As a result, a 10 W oil will be thicker than a 5W oil in the winter.

The 40 rating

At higher temperatures, the oil’s viscosity increases to this level. 212 Fahrenheit is the ideal temperature for the best oil flow in an engine (100 degrees Celsius). The hot viscosity rating measures how well a lubricant protects engine parts and prevents leaking from seals even when it is at a thinner consistency. 40 is the high-temperature viscosity under heated circumstances (summer).

Temperature range

When using 10W-40 engine oil, the optimum ambient temperature range is between 30 and 40 degrees Celsius (22 to 104 degrees Fahrenheit).

The 10W40 engine oil API

API CI 4/SL identifies the 10W-40 engine oil.

Uses of 10W -40 engine oil

The heavy and heavy duty gasoline engines in light trucks continue to use this oil despite the fact that it is not recommended for modern passenger cars. Motorcycle engines and diesel engines are the primary users of the oil’s weight.

The oil’s viscosity serves as a replacement for older motors with oil leaking or burning problems. Due to its greater viscosity while the engine is hot, this causes it to flow more slowly. Thus, it is feasible to lubricate the moving parts of an ancient engine with high mileage without the risk of leaks.

In addition, the greater viscosity of the oil makes it an excellent choice for motors whose oil temperatures are high since it can withstand the high temperatures thermal breakdown that occurs when the oil is heated.

Because synthetic oils flow better than conventional engine oils and keep sufficient viscosity to protect piston bearings and skirts at high temperatures, 10W 40 is a suitable choice for smoother starting protection.

15W50 engine oil

15w50 Oil Temperature Range

In addition to a few specified additives, 15W50 motor oil consists of semi-synthetic oils. Designed specifically for current four-stroke engines, this oil provides maximum performance in any engine.

The motor oil is classed as 15W50 by the SAE. The viscosity and flow characteristics of an oil are described by the SAE class in the same way.

It is important to note that motor oils in the 15W50 classification are multi-grade oils, meaning that they perform well in both hot and cold environments. The oil’s cold temperature flow ability is designated as 15W, whereas Winter is designated as W.

Pumping enough lubricant into an engine is possible even at temperatures as low as -25 degrees celsius (-13 degrees Fahrenheit). The 50 refers to the oil’s capacity to operate at a temperature of 100 degrees Celsius without burning up.

15W50 oil viscosity index

The oil’s viscosity ranges from 16.3 to 21.8mm2/s at 100 degrees Celsius.

15W50 Temperature range

15w50 Oil Temperature Range

A wide variety of temperatures can be protected with 15W50 engine oil. Low temperature flow and heat tolerance allow the oil to survive temperatures up to 131°F without deterioration.

As a result, it has a temperature range of 13 to 131 degrees Fahrenheit. This aids the oil in preventing the accumulation of superfluous deposits in the engine, hence extending the life of the engine.

Differences between 10w40 vs. 15w50

Although both oils can be used effectively, there are some differences between the two. They are as follows:

  • The 10W 40 oil has a better flowability at cold temperatures than the 15W engine oil. This is because the 15W -50 oil is thicker at low temperatures than the 10W-40 so, it will not flow well at startups. However, it is best at high temperatures because it is thicker and therefore maintains its viscosity even when temperatures rise. 
  • Because it is thinner, the 10W40 flows well at high temperatures leaving no residue in the engine. 
  • The 15W-50 engine oil is better for use during Winter than the 10W-40. 
  • 10W -40 is denser or thicker than what most engine manufacturers recommend. 15W, on the other hand, increases wear fuel consumption and reduces power. So, it is better to consult the car manual as it will indicate which oil is better for your engine. 

What happens if you put oil that the car manufacturer does not recommend?

Transmission failure, poor lubrication, and overheating might occur if you use the wrong oil for your vehicle’s engine. Since an engine damaged by the improper oil cannot be repaired, it is critical that you use the oil that your car’s manufacturer advises in order to avoid any damage or losses.


Engine oil is essential to the efficient operation of the vehicle’s engine. To be clear: Not every engine is a good match for every automobile engine. Both the 10W40 and the 15W50 engine oils are great choices for the engines for which they are intended.

High-performance vehicles, such as race cars, should use 15W50 engine oil. During the colder months, its thickness may make it unsuitable for use.