5w20 vs 5w30 – What’s The Difference Between Them – Transmissions.biz

motor oil viscosity explained

The 5w20 and 5w30 motor oils are the best for use in older vehicles that require lower weight oil. The difference between them is their viscosity, where the 5W-20 has a higher viscosity than the 5W-30. This can have an impact on how well they work with your engine, but it will depend on what vehicle you drive and what type of driving you do. In this blog post, we’ll discuss more these types of oils and help you decide which one to choose!


Undoubtedly, it’s crucial to choose the proper kind of motor oil for your vehicle in order to ensure its smooth running. Neglecting your motor, you will definitely fail to feel all the benefits of your car.

Clearly, many automobile owners turn to professional mechanics to change the oil. However, even if you don’t change the oil yourself, it doesn’t mean that you can be unaware of what’s going on inside your vehicle. Remember that you need to understand what oil is the most appropriate for your engine. This information can be of great use for you if you have no possibility to turn to a professional.

In order to maintain a motor in good condition, every car owner needs to change the oil in time. Here, we offer you a comparison of 5w20 and 5w30 motor oils as both of them work great in hot as well as cold temperatures.

What Is Oil Viscosity?

The Society of Automotive Engineers differentiates motor oils by their viscosity features from low to high: 0, 5, 10, 15, 20, 25, 30, 40, 50 and 60. In short, viscosity means liquid’s resistance to travel.motor oil viscosity explained

Too watery liquids have low viscosity ratings while thick fluids (like honey) have high viscosity levels. Letter W usually stands behind numbers 0, 5, 10, 15 and 25, signifying “winter” or low temperatures, not weight. Remember that the viscosity index of the motor oil may change depending on temperature and weather conditions.

Nevertheless, talking about kinematic viscosity, the index is based on oil’s aptitude to travel through a conventional port at standard temperatures. The longer it streams, the higher the SAE rating it gets. Thus, it’s evident that 5w30’s viscosity exceeds the one of 5w20.

Multi Grade Motor Oil

There are many types of motor oil, each with a different viscosity rating at a certain temperature. In the case of 5W-20, the numbers mean that it has two different viscosities: one for winter and one for summer driving. Oil includes polymers (molecules) that increase in size as temperatures rise to maintain lubrication properties.

The Winter Rating (indicated by the letter W) tells you how thick the oil will be at a cold winter temperature. The Summer rating (indicated by the letter S) tells you how thick the oil will be when exposed to hot summer conditions.

Difference Between 5w20 and 5w30 Motor Oil

As we have already mentioned, W signifies “winter”.

The number before this letter signifies the oil weight in cold or non-heated ambiance. Cold climate or frosty season may affect the oil weight and the way it runs through the motor.

5w20’s Winter rating equals 5 and will operate as a 20 weight oil with heat. Long ago, when this rating of engine oils was first created, cars were driven much easier in winter than today. The thing is that they had no 4-wheel drive abilities, peculiar to contemporary SUVs and other automobiles. Consequently, winter viscosity wasn’t a problem for drivers.

Nowadays drivers must take care that they are applying only the advisable type of motor oil. In order to see the importance of choosing the right oil, you should be aware of the fundamental formulas for motor oil. The higher the rating, the thicker the oil is. Thus, 5w30 will flow less smoothly than 5w20. When the motor is cool, its viscosity is almost identical. However, when it operates, it heats and the difference is pretty observable.

Consequently, 5w30’s winter index is the same, but it operates as a 30 weight oil in the heated ambiance.

You should know that many cars accept oils with a couple of possible viscosity levels. Thus, you will not face any serious troubles with your engine by applying 5w30 instead of 5w20.

However, it’s crucial to know what exactly your vehicle needs and provide it with the best possible option.

Let’s see the main differences between 5W-30 and 5W-20 of Castrol GTX motor oil:

Characteristics Castrol GTX 5W-30 High Mileage Engine Oil Castrol GTX 5W-20 High Mileage Engine Oil
SAE Grade 5W-30 5W-20
API Service SN Plus SN Plus
Flammable No No
Motor Oil Type Conventional Conventional
Maximum Operating Temperature (°C) 180 180
Maximum Operating Temperature (°F) 356 356
Minimum Operating Temperature (°C) -35 -35
Minimum Operating Temperature (°F) -31 -31
Pour Point (°C) -39 -48
Pour Point (°F) -38 -54
Flash Point (°C) 200 200
Flash Point (°F) 392 392

How is 5w20 Different From 5w30 at Operating Temperature?

5w20 vs 5w30 – what is the difference?

At 100 degrees Celsius, 5w30 is going to be slightly more viscous than a 5w20. Because the viscosity of the 5w30 oil will cause less drag and allow for smoother movement around your engine parts it can also have a negative impact on your horsepower, but you can get slightly lower fuel economy.

The difference in the two grades of motor oil is minimal, and you probably won’t notice a decrease in fuel efficiency by switching from one to the other. However, over time savings at the pump can add up. That said, it would not be advisable to switch if there’s an engine-factory specification that prohibits it.

5w20 vs 5w30: Which Oil Ensures Better Gas Mileage?

Oils with lower viscosity like 5w20 build a thinner block of protection at normal temperatures. As the lesser amount of oil is in between the moving details of your motor, it will provide better performance due to low friction. Thus, the application of low viscosity engine oil leads to enhanced fuel efficiency.

Though the raise in your MPG maybe not be evident, still, it will have some enhancements. Some automotive forums and blogs claim that better fuel efficiency demands extra investments. Actually, many experts assure that usage of 5w20 instead of 5w30 will inevitably ruin your motor and lead to its shorter lifespan.

So, 5w20 and other low viscosity oils will give less protection to the motor than the ones with higher ratings in regular conditions.

Simultaneously, it’s more reasonable to apply them in regions with cold climates and frosty weather as they will guarantee more efficient motor functioning under low temperatures.

What Is Better: 5w20 or 5w30?

Seeking the best oil for your car, several factors must be considered. Though both these oils have approximately the same level of protection provided, they still differ in their viscosity index. If you dwell in a hot region, 5w30 is most appropriate as it functions better at high temperatures and protects your motor more efficiently.

However, 5w20 is a better option for a cold climate as it’s more fluid and heats up faster. If you live in a region with a mild climate, both oils are appropriate.

Can You Mix 5w20 and 5w30 motor oils?

Many vehicles can operate on either 5w20 or 5w30 grade oil, so mixing the two types of motor oils won’t cause any damage to your engine.

However, if your engine is not made for 5w-30 oil, mixing in that with 5w-20 will cause it to strain and wear more quickly.

Keep in mind that you might void your warranty if you use the wrong kind of oil in your engine while your car is still under warranty. That’s why checking the owner’s manual before doing anything like this is so important.

Is 5w20 Oil Good for High Mileage?

So, in most cases, it means NO!

The type of oil that’s best for your vehicle is one you should consult with the manual. If it specifies 5w20, then that is always the best option, regardless of whether or not you drive a lot because your car and engine were designed to work with this formulation.

Of course, there are a number of potential different oils you can buy as well as some that claim to include additives, but these things can at best only be theorized to improve performance. In reality, it’s all about the oil and motor vehicle engine formulation and manufacturer specs.

Stick with the recommended 5W30 in your owner’s manual. If unsure about any gear or gadgets claiming improved performance for high mileage vehicles, make sure you research specific brands and variants beforehand to ensure they work with your vehicle before purchasing anything.

To Sum It Up

Synthetic motor oils are versatile. Thus, both 5w20 and 5w30 will function properly to ensure the necessary level of protection for your engine no matter what climate you live in. However, if you are still contemplating on what option is the best for your automobile, give preference to 5w30.

Compared to 5w-20, 5w-30 keeps a greater level of film and shear strength. Moreover, it operates smoothly regardless of automobile type, ambiance, and temperature. Though, it’s important to keep in mind that the difference is rather mild and so, you are free to opt for 5w20 if you fail to find 5w30.

Motor Oil FAQs

What Motor Oils Do and Don’t Do?

Motor oils lubricate the engine to help reduce friction and prevent heat from building up. It also protects the engine by reducing wear and corrosion, as well as preventing air pollution inside an automobile’s combustion chamber. Motor oil is essential for a car, but this doesn’t mean that the best motor oil can prevent leakages unless you take care of your engine.

Can I Use 5w30 Instead of 5w20?

Industry experts recommend 5w30 motor oil because it is a more viscous medium that provides higher level of engine protection than the 5w20.

What If I Use 5w20 on a 5w30 Car?

This is unfortunate, but 5w20 engine oil is not an appropriate choice. This type of oil will be too thin for your engine and cannot provide the required protection. In general, a 5w20 motor oil will have less additives as they shear less under normal operating conditions.

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