5w20 vs 5w30 – Which Oil Is Best For Your Car?

The major difference between 5w20 vs 5w30 is viscosity.

Viscosity is the resistance of an oil to flow. The higher the number on the oil model is, the thicker the oil and the thicker the oil , the harder it is to get thin under the influence of heat.

Regular oil tends to lose its viscosity when subjected to heat and given the environment where it is being used, exposure to heat cannot be prevented. For this reason, different engine oil types with different viscosity ratings, i.e different degrees of resistance to heat, have been manufactured for different vehicles operating in different climatic regions.

This article takes a look at 5w20 vs 5w30 to help you understand which one is best for your vehicle.



Understand The Basics

The number before the letter “W” represents the cold viscosity of the oil. In simpler terms, this is the rating of the engine oil based on its performance in cold environments.

This comes in handy when driving in very cold countries like Korea, Russia or in winter seasons in any country. In these areas or during these seasons, your engine might be subjected to the cold weather when driving or while parked. When this happens, if the cold viscosity of the engine oil is not strong enough, the oil will be too thick to lubricate the engine, the fuel efficiency is compromised and the engine suffers.

The number after the letter “W” represents the hot viscosity of the oil, meaning the oil’s resistance to heat. This number has the most variations in all the oil types given that engines tend to get hotter more than they are exposed to cold.

Given this explanation , i believe you should be able to decide which is best for your car. To be clear though, the rating of these engine oil types are measured in zero-degree Celsius. 5W represents viscosity at zero degrees, but for regular oils, 5W is too thin for normal car temperature which is why it is available in different variations.


What Is The Difference Between 5w20 and 5w30

Without beating about the bush , the difference between 5w20 and 5w30 is their viscosity.  5w20 is lighter , creates less friction and drag and is best for cold temperatures. On the hand 5w30 is thicker and is best for warm temperatures.

In terms of viscosity , 5w20 has a viscosity grade of 8.9 at 1000C while that of the 5w30 is 11.0. Given this difference, it is pretty clear why the 5w30 is the most common of the duo. At 400C, which is basically normal vehicle temperature, the viscosity of  5W20 is 49.8, while that of  5W30 is 61.7.

The viscosity indices of both products are 160 and 172 respectively with a common flash point of 230 each.

Which of them is best for your vehicle?

Choosing the best for your vehicle depends on the temperature in your region. If you live in a cold region you’ld be better of investing in an oil with thinner viscosity and the 5W20 should be your consideration. If you live in a warm region the 5W30 oil would be the best choice for your car.

Synthetic OilOil TypeCheck Price
1). Royal Purple HPS5W20
2). Mobil 1 (120768) High Mileage5W20
3). Castrol 03083 5W20
1). Mobil 1 (120766)5W30
2). Castrol 030875W30
3). Valvoline 7822565W30


How do these two products affect the gas mileage of your vehicle?

The thinner the engine oil gets, the less effective it becomes and this goes on to affect the fuel efficiency of the vehicle and cause the engine parts to wear out faster. However, another effect of engine oil rating and performance on your vehicle is its influence on the gas mileage.

This is basically an extension of the fuel efficiency as gas mileage is a term used to explain the consumption and conversion rate of gas in the engine.

An engine oil with a lower viscosity such as 5w20 will become thinner at normal operating temperature. Given its new texture based on the influence of the engine’s temperature, the oil will flow easily to the hard to reach spots, provide less friction for the engine parts and inspire better performance.

However, fuel efficiency comes at a great cost because the engine oil eventually gets too thin to reduce friction when the temperature inevitably spikes up. There will be a huge jump in your MPG despite the improvement in your fuel economy.

Therefore, while the 5w20 is pretty good at normal temperatures, when it becomes thin enough to improve your gas mileage, there will be a compromise in the lubrication of the engine leading to wear and tear.


Conclusively, the key to using these products lies in understanding their strengths and weaknesses in relation to your engine’s requirements. Since engine oils with lower viscosity are better suited to regions with lower average temperatures and freezing conditions, the 5w20 seems like a perfect fit here.

However, the 5w30 still remains the most popular options because of its wide adaptation range, but given the price, you could get the 5w20 if it’s good enough for your engine. You could get a confirmation on that from your auto mechanic or the manufacturer’s guide.

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