Is it harmful to use 15W-50 grade oil instead of 20W-40?

The answer is YES, Engine oil is graded according to specific criteria. When manufacturers recommend certain grades for certain vehicles, it is done keeping in mind the requirements of that specific engine. This is why one should avoid switching engine oil grades to prevent damage to the engine. So, when it comes to engine oil, it is safer to stick to the grade recommended by the manufacturer for that particular vehicle. 

What is ‘grade’ in engine oil?

Engine oils are graded on a scale that has been developed by the Society of Automotive Engineers (SAE). The main function of these grades is to describe the viscosity of the Engine oil

Simply put, the engine oil grades help differentiate between oils with varying thickness. The higher a grade is, the thicker the oil. This means that 20W-50 grade oil is thicker than 15W-50 grade oil. 

What are the two numbers in an oil grade?

When it comes to engine oil viscosity, outside temperature is important. When it is cold, the oil is thicker while when it is warm outside, the oil becomes thinner. 

The two numbers in a multi-weight oil grade help differentiate according to temperature. Hence, for example, in 15W-50, 15 is the grade when cold and 50 is the grade when warm.

What does the ‘W’ stand for?

As stated before, the outside temperature plays an important role in the thickness of oil. This is why there needs to be differentiation within the grade when cold and when warm. 

The ‘W’ in a grade stands for ‘Winter’, indicating lower temperatures. 20W-50 grade oil indicates that the grade of the oil is 20 in winter, going up to 50 in the summer.

What’s the difference between 15W-50 and 20W-50?

According to grading norms explained previously, the numbers of a grade denote oil viscosity. Thus, 15W-50 has 15 grade in winter and 50 grade in the warm, while 20W-50 has 20 grade in winter and 50 grade in warmer temperatures. 

Since higher grade denotes higher viscosity, 20W-50 is thicker or more viscous than 15W-50 grade oil. 

What is 15W-50 oil used for?

Generally 15W-50 grade oil has been used in motorsports and racing, where engines are stressed due to high revving, heat and speed. Furthermore, this oil is suitable to use in high-performance turbo-charged, supercharger multi-valve fuel injected engines found in cars, light vans and trucks.

When can 20W-50 oil be used?

20W-50 grade oil should be used for vehicles that specify that grade for usage. Generally, this engine oil is used in cars designed for higher temperatures (summer cars) during winter times i.e. when warm weather cars are used in cold weather

Will thicker oil damage my engine?

Drivers use thicker engine oil in their engines for various reasons. Many believe that thicker oil will provide better lubrication for their engine and while this is true to an extent, it is not completely safe. 

Recommendations for specific grades are deliberate and are made keeping in mind the design of the engine. For engines with smaller spaces between moving parts, thicker oil can be harmful and may not flow easily. Thus, it is safer to use the grade recommended by the manufacturer.

Which oil grade is better: 15W-50 or 20W-50?

When it comes to suitability of oil grades, there is no better or worse, since the type of oil to be used depends on the engine of the vehicle and the weather. The decision of which grade oil is better therefore is variable. 

Overall, since 20W-50 grade oil is thicker, it is more suitable for warm weather when oil tends to thin in the heat. On the other hand, 15W-50 can be considered better in colder climates since it would not become too thick in the cold. 

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