What is the difference between 20w40 and 20w50 Engine Oil?

When it comes to using engine oils for your bikes or cars, there are many things you need to consider. Our previous blog dove into detail about how to choose the right oil for yourself. One of the points we touched upon in the article was engine oil grades: What is the difference between 20w40 and 20w50 Engine Oil? 

Engine oils have standards to help us check the viscosity of the lubricant at specific temperatures. All of the information determines whether the engine oil will work smoothly and efficiently. 

However, there are some aspects of these standards that can seem confusing. Such as using a 20w40 or 20w50 engine oil for your vehicle or bike. Hence, it’s convenient to know the details behind what these grades mean and how they differ from each other.  

Engine Oil Viscosity

Before we leap into the world of engine oil standards, let us reflect upon engine oils and it’s viscosity. Engine oils lubricate the engine to avoid wear and corrosion of the internal parts.

They maintain the smooth and effective running of the engine. It also helps cool the engine. Now since they are lubricants, the thickness of the fluid plays a huge role in protecting the internal parts we talked about. 

Viscosity is the resistance of a fluid to flow. In engine oils, how thin and thick the lubricant is, decides how the engine will run smoothly and without any hindrance. One important thing to note here is that different temperatures affect viscosity. At high temperatures, the lubricant will thin out and at low temperatures, it will thicken. 

This relates to the climate where you will drive and make use of your bike, car, auto-rickshaw or heavy vehicle. If you’re driving at a place with relatively high temperatures, it is recommended you use highly viscous engine oils.

This will ensure they won’t thin out in extremely hot conditions as well. On the contrary, engine oils with low viscosity are for colder locations because they are thin. The ability of the lubricant to flow ensures resistance to thickening.

Besides, you have to be mindful of regular oil changes of the lubricant while topping up or purchasing a new engine oil. 

Engine Oil Grades

There are various scales to categorize engine oils for varying purposes. This is so we can better understand the different properties and qualities of the engine oils at varying temperatures. Given below are popular engine oil standards we need to be aware of;

  1. American Petroleum Institute (API) – A US-based trade association that certifies whether the oil meets OEM (Original Equipment Manufacturer’s) specifications and quality.
  2. Society of Automotive Engineers (SAE) – SAE international from the US has developed widely known standards known as the SAE number or code which determines the engine oil viscosity. 

We are specifically concerned with SAE numerical code. This is how to interpret them: 

It is important to note that the oil will flow more easily at low numbers. 

For example; 20W-40 is an SAE grade where 20W (Winter) is 20-weight/viscosity of oil for colder temperatures and 40 is 40-weight or oil viscosity at low temperature.  

What is the difference between 20w40 and 20w50 Engine Oil?

20W-40 is a multigrade oil which means it can operate in both colder and hotter conditions. It is both a petrol and diesel engine oil which is why it is a lucrative option to choose. 

Benefits of using 20W40 are;

  1. Superior Performance
  2. High Viscosity
  3. Better Thermal Stability
  4. Good Cleaning Capacity
  5. Anti-Wear Qualities
  6. Drain Interval Extended
  7. High Clutch Friction Properties 

This engine oil grade is traditional high-performing engine oil. They’re made so they can pass weights for a wide variety.  It is most commonly used for four-stroke motorcycles and their engines.

It gives high viscosity index, to give maximum performance out of the engine and has good dirt dispensing capacity. Another advantage of thin oils like these is that they maintain film strength and you don’t have to worry about oil pressure during hotter conditions and loads.

20W50 is also a muti-viscosity oil. These lubricants are thicker and highly viscous which is why they perform better at hotter temperatures and warmer climates.

Any other oil with a different viscosity will be forced to thin out in the said climate but this oil will maintain its thickness and aid in good engine performance.

It is said to offer cushioning and protection against friction and corrosion in the engine system. Furthermore, it is a good sealant and that results in the extension of the engine oil life. 20 degrees celsius is the minimum temperature the oil will flow at. At 100 degree celsius, its viscosity rating is 50. 

They are generally used for older vehicles but it is believed that since they are equipped for high loads, they facilitate race engines. It offers good viscosity, however it offers less horsepower and there is a chance, it may decrease the crankshaft functioning. 

The disadvantage of using 20w-50 is that is more fuel consuming. This oil grade is not suitable for modern engines because of the thickness of the fluid. 

They tend to move towards more sensitive-prone areas of the engine and that will cause more harm than good. Another drawback is the high viscosity property which is useful for warmer climates but will hamper during cold start and colder temperatures.’

Because the lubricant is not thin, it is highly likely to damage and wear the internal parts of the engine. Oils that are more viscous also increase the oil pressure.

20W50 is also known to cause;

  1. Sludge
  2. Extreme engine wear
  3. Clogged PCV systems
  4. Seized timing adjusters / variators
  5. Poor gas mileage
  6. Damaged timing chain tensioners
  7. Premature turbo bearing failure
  8. Premature oil pump failure

It is believed that at both 40 weight and 50 weight, they both still offer the same viscosity once exposed to high temperatures. But even so, both vary in their properties.

The main objective of engine oil is to support the engine’s smooth performance with proper lubrication and cleaning. 20W40 is suitable for hotter climates and will not cause sludge as opposed to 20w50 which is more appropriate for hotter conditions.

But, it has more drawbacks than 20w40. For example, it will only pass two or three cold starts in a colder climate but nothing beyond that.  


One crucial point to note here is that before oiling your engine, you need to check the OEM specifications. It goes without saying that your vehicle manufacturer’s manual will mention the right viscosity grade and which specific type of engine oil will work best for your car or bike. 

Whether a mineral engine oil is more apt or synthetic or semi-synthetic will be more fitting, the related information can be found in the manual. That is why it has been rightfully called your best friend during these situations. 

This might seem a lot of things to keep a note of but a basic understanding of engine oil grade is always a plus. It will ensure you that get the most out of your two, three or four-wheelers and maintain efficiency at different temperatures. 

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