comparing oils on the shelf in store

5W20 vs 5W30 Oil: What’s the Difference?

For those that are not mechanically-minded, basic car maintenance can sometimes be a significant source of stress. Cars are expensive and dangerous pieces of machinery, and we all understand the importance of keeping them running smoothly for a long time.

But somehow we’re expected to change oil and gas, diagnose faults, and even blow up our own tires! Filling up gas is easy enough, but oil can get confusing. Not only do you have to figure out how to open up the bonnet and use the dipstick, but you also need to effectively choose the right type of oil to put in!

In this post, we’re going to examine two extremely common types of car oil:

  • 5W20 – This oil is really “fluid” at lower temperatures, making the process of starting your cold engine much easier. It is recommended for use at -35°C up to +25°C (outside temperature).
  • 5W30 – This oil has the same viscosity at lower temperatures. However, it is a little bit thicker at higher temperatures than 5W20. It is recommended for use at -35°C up to +35°C (outside temperature).

We’ll explore the differences and help you to make the right choice for your engine. And in doing so, you should gain a better understanding of the differences and even how oil is graded.

5W20 vs 5W30

What do the Numbers Mean?


The first sequence of numbers (before W) refers to the viscosity of the oil at low temperatures. 


The letter W refers to the word “winter” & is used to differentiate the oil’s viscosity at cold & hot temperatures. 


The second sequence of numbers (after W) refers to the viscosity of the oil at high temperatures (100 °C). 

First: you may be wondering what the difference between these two types of oil is. What do these numbers mean, and what do they tell you about the type of oil you’re choosing?

Essentially, all this grading system tells you about is the viscosity of your oil. Here, a lower number denotes a lower amount of viscosity, while a higher number represents a higher amount!

Viscosity is thickness and stickiness.

An example of a viscous liquid is honey, for instance, whereas water has a very low viscosity. The faster a liquid pours then, the lower its viscosity.

The reason you have two numbers is that the chemical properties of oil alter depending on temperature. When it is cold, oil is typically less viscous. It then thickens up when it gets hot.

This is important, seeing as your car may well be sitting outside for long periods when it’s cold outside. At the same time, though, when an engine runs, it gets very hot and thereby heats up the oil in the engine.

The first number then is the viscosity when it is cold – during winter, or when the car isn’t moving. In fact, the “W” stands for winter.

Both these types of oil, therefore, have a low viscosity during winter and when not in use. That’s because both types of oil are 5W, rather than 10W or 15W – both of which also exist.

5W is a good starting point when choosing an oil, as it means the oil will be runny when the engine starts, helping it to move more quickly through the system. Moreover, it also means that the oil will be able to withstand cold temperatures better than a 10W or 15W oil. Those latter types are generally only suitable to warmer climates.

The second number is what we’re interested in. This tells you the viscosity of the oil under operating temperatures. So when the engine is running, and the oil heats up, a 5W30 oil will get much thicker than a 5W20 oil.

Why Viscosity is Important

What it Does for Your Engine

If a runny oil travels more quickly to the engine, why would you choose a thicker oil at all? The answer is that once inside the engine, the thicker oil is better able to do its job.

The purpose of oil is essentially to coat the surfaces of the different components in an engine.

By doing this, those components won’t be able to come into direct contact. This allows them to glide over each other, due to the well-lubricated surfaces. In contrast, if the oil were not there, then the metal surfaces would grind against one another, which would lead to a more rapid breakdown and degradation of the metal.

This is how a higher quality oil – and particularly a thicker oil – can help to maintain the performance of your vehicle for longer.

In fact, if your oil is very runny, then it may even get thrown off of the mechanical parts as they move. This can leave those parts virtually naked, and thereby more likely to get damaged. Another consideration is that a very runny oil will leak more quickly if there is any damage to the engine.

In fact, if you do have a minor oil leak, switching to a slightly higher grade of oil can actually be enough to stop the leak in some cases!

Choosing The Best Oil For Your Generator?​

Which is Right for You?

Should you use 5W20 or 5W30?

As mentioned, runnier oil will move more quickly when it is cool. This can additionally mean that it moves more easily inside the engine once heated up.

However, in very high temperatures, thinner oils can break down more quickly.

You may be wondering where oil goes when you run your car! While some will get thrown from the vehicle, a lot of it will remain in the engine but can break down to form a kind of thick sludge. With proper maintenance, you can keep this at bay and ensure your car has a long and happy life – but there is no way to entirely prevent that sludge build up.

It’s for this reason, that you may choose a higher grade of oil during hotter climates.

Moreover, some types of engine will prefer a thicker type of oil in order to provide more protection. This, combined with greater chemical stability, means that 5W30 is the slightly more widely used oil of the two.

To break it down then:

  • Use 5W30 in warmer climates
  • Use 5W20 in cooler climates
  • Most people will fall into the first category

The One Simple Rule

You need to follow

With that said though, there is one straightforward way to make this decision much easier: follow the manufacturer’s guidelines.

You’ll find that when you take a look in the manual that came with your vehicle or generator, it will tell you the ideal oil to use, and a range of oils that you can choose from.

Not only that, but it may well let you know whether to change your oil type in particular weather conditions.

This makes it very clear which oil you should use, and that in turn will guarantee that your vehicle enjoys the best economy, while also protecting the engine, so it runs better, for longer.

If in doubt, just follow the instructions that came with your car! It’s easy!

Can you mix these

Will it cause any damage?

One question a lot of people have about 5W20 and 5W30 oil is whether they can be mixed. The answer is that they can indeed be mixed, though this shouldn’t be your preferred strategy.

When you mix 5W20 and 5W30, you will be left with some of the downsides of both types of oil.

That is to say that the oil you’re left with could still be quicker to freeze, while also breaking down in warm temperatures. But with that said, the difference is not great enough for this to be an issue in most cases – as long as your vehicle will accept both types.

This certainly won’t be an issue if you are forced to change oil and you have to switch to a different type – they will mix, and no harm will be done!

Mineral vs Synthetic Oil

What is the difference

Another decision you need to make when choosing either type of oil is whether you want to use synthetic or mineral. Mineral oil is also called “regular” oil, seeing as it is made from natural resources just like oil has been for the longest time.

Synthetic oil is slightly newer.

This is an artificially created (synthesized) oil that has been designed to offer more benefits to the driver. In some cases, the synthetic oil started as a mineral oil but had additional ingredients added in.

In other cases, the oil is entirely artificial.

The additives included in synthetic oil have a number of different jobs. They help to slow the breakdown of your oil, they help to coat the mechanical parts better, and they may even be able to plug a leak.

Generally, synthetic oil is, therefore, better for your car AND lasts much longer. Whereas a refill of regular oil might be good for 200-500 miles, a synthetic oil change could last you 700 miles up to 1,500 miles!

This means that you will get your money back in the long term.

Conclusion: Don’t Fret

While there may be a lot of different factors to consider when choosing oil, the simplest instruction is just to follow the guidelines in your manual.

They are there for a reason, and this will ensure you get the most efficient oil that protects your car or generator in the long term.

But with that said, if you use the “wrong” type of oil, this won’t normally be a problem unless you live in extreme weather conditions. Mixing oils isn’t a big deal either. 

So now you know, you can buy with confidence!

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About the author

Hands behind everything you see around. Matthew is the main workforce that puts all ideas into realization. So, do not feed him bad ideas.


handyman, loves science

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