5W20 vs 5W30

5W20 vs 5W30 – What’s the Best Oil For Your Car?

We compare 2 of the most common motor oils for cars: we will be exploring the similarities and differences between 5W20 vs 5W30.

The motor oil is a critical part of the car. Its main focus is, as you would probably expect, lubrication. It keeps everything running smoothly. Your oil is also partially responsible for cooling and, in some way, assists the coolant system. We’ll go into this in more detail later on down the page.

For the purposes of today, we’ll try to keep everything focused in on 5W20 vs 5W30.

If you’re familiar with how multi-grade motor oil is graded, click here to skip down to the section where we compare 5W20 vs 5W30. Also, if you have any questions or comments, feel free to leave one at the bottom of the article and we’ll get back to you.

Right then. Let’s get started.

5W20 vs 5W30 – What Do the Numbers Mean?

Someone who isn’t familiar with the way motor oil is graded might be immediately put off by the strange “number”, “letter”, “number” system that manufacturers use to describe their products. It’s true. It can be very overwhelming.

Don’t worry, though – we will walk through it step by step.

This way of “grading” oils was standardized by the Society of Automotive Engineers – or the SAE. It refers to multi-grade oils – that is, oils with more than 1 grade.

If we use one of the above oils as an example, say “5W30”, this might help.

You can see that there are 2 separate numbers used to describe this product – a “5” and a “30”. These are the 2 different “grades” which make the oil “multi-grade”.

(Technically, the “W” is attached to the “5”, so it reads “5W-30”, but don’t worry about that just yet. We’ll come to it.)

These numbers represent relative viscosity. Let’s now look at viscosity in greater depth.

What is Viscosity?

Viscosity, in simple terms, is how thick a liquid is.

The thicker a liquid is, the more viscous it is. For example, you might think of custard or a good, thick, beef gravy.

And, vice versa, the thinner a liquid is, the less viscous it is. Water or skimmed milk would be good examples of this.

To define it properly – scientifically – we would say that viscosity relates to the amount of internal friction as it moves. Check out princeton.edu for a full definition.

Liquids become less viscous at higher temperatures. That is, when they’re cold, they are thick, but as they’re warmed up, they become thinner. Motor oil is no exception to this.

In terms of engines, this is kind of the opposite of what we want. When a car starts up, it has to be able to pump oil all round the engine quickly. If the oil was to be too thick, this puts much more strain on the oil pump and also means that it won’t be able to flow all around the engine as efficiently as if it was thinner. Therefore, when the oil is cold, we generally want it to be as thin as possible.

Also, once the engine is up to temperature, the oil naturally becomes thinner, but we want it to be as good at lubricating as possible. In most motors, this requires an oil that is as thick as efficiently possible.

This is why we use synthetic multi-grade motor oils. Viscosities can be modified to whatever the manufacturer needs for the car and the climate it is being sold in.

What Does the “W” Mean?

We mentioned earlier that, technically, the oil is made up of 2 gradings – the first number and the second one. In the case of 5W30 oil, this is made up of “5W” and “30”. So, we’ve looked at the numbers and how they represent relative viscosity, but what does the “W” mean?

The W is indicative of the viscosity in cold temperatures. It quite literally stands for “winter”.

The number before shows the oil’s relative viscosity in winter. Going back to our 5W30 example, we can see that this oil has a relative viscosity of 5 in the cold.

By contrast, the other number is often thought of as, quite simply, “not winter”. 5W30 would have a relative viscosity of 30 in “not winter” conditions.

In reality, these 2 numbers are really talking about the motor’s starting and running temperatures.

These 2 numbers are not related to each other! “5W” is actually more viscous than “30” at their own measured temperature rating.

When you come to a car in the morning, it is typically cold – unless you live in a particularly warm climate, of course. When you start the car at this time, it is referred to as a “cold start”. Don’t ask me where automotive engineers get their inventive terms from. The first grading number in the oil, in symbol, is referring to the oil’s viscosity at this moment.

Once the car is running, it has to get up to its optimal operating temperature. This is the gauge you see on the dashboard and is usually about 100 degrees C. The second number of the oil is (approximately) the relative viscosity of the oil at this time.

5W20 vs 5W30 – How Do They Compare?

Using the above definitions, then, we can describe these 2 oils in comparison to each other. 5W20 vs 5W30. Which is best?

Both have a winter rating of 5W. This means that, when your motor is cold, for example when you come to it in the morning, it will have a relative viscosity of SAE 5. This is nice and easy to pump around your motor quickly, while things are getting warmed up.

Since both oils are the same in these conditions, there isn’t much to compare.

At operating temperatures, however, there is a difference. 5W20 has a lower viscosity at this point than 5W30. This is as simple to know as “20 is less than 30”. This means that 5W20 is thinner than 5W30 when your motor is running at its operating temperature.

For this reason, 5W30 is more likely to be used in bigger engines that reach higher internal temperatures – at least, in comparison to 5W20. The vice versa is also true, obviously – you would be more likely to find 5W20 in a smaller-engined vehicle than 5W30.

This is the only real difference between 5W20 vs 5W30.

There may be other differences, but these will come from the manufacturers. Multi-grade oils are usually made with a variety of additives. These help with things such as keeping the engine clean, free from sludge, environmentally-friendly, etc. Different manufacturers will use different additives and different amounts of them, too.

Overall, there is very little difference between 5W20 vs 5W30.

You should always consult your owner’s manual for the correct information regarding which oil to put in.

Motor Oil Disposal

5W20 vs 5W30 – Why Are There So Many Different Types of Motor Oil?

We have been thinking about 5W20 vs 5W30, but there are a whole range of multi-grade motor oils that you could come across. Some motors take oils with viscosities as low as 0W20 – or even less – while some need 15W40. So, why are there so many?

The answer is perhaps an obvious one – because there are lots of different types of motor.

A car’s engine is designed alongside it – it is supposed to be as complementary to the car’s purpose, style, and shape as possible, giving a smooth drive.

In general, the larger the motor is, the more viscous the oil has to be when at operating temperature. This helps to keep everything lubricated and running well.

There are now many exceptions to this rule.

The main one is probably the increased dependence on forced induction, better known to most of us as superchargers and turbochargers.

These are used more and more in the design of cars to reduce environmental impact. Using them allows for the motor to spend less force “sucking” air into the engine, and by this process means that the car is more environmentally-friendly. There are also other benefits, and this means that the engines are more efficient. Read about these on Supercharger Forums here.

As these engines become more efficient, the motor oil is not required to be so viscous. This is why many small, modern cars use multi-grade oils with very low viscosities, such as 0W20.

By contrast, in large, diesel trucks, an awful lot of lubrication is needed. For example, the compression ratios inside diesel engines are much higher.

As a result, you are more likely to find more viscous oils, such as 15W40, in vehicles like these.

5W20 vs 5W30 – What Would Happen If I Used the Wrong Motor Oil?

If you were to use the wrong kind of motor oil in your car, you should immediately stop the engine, drain the oil, and replace it with the right kind. Of course, don’t do this on the side of the highway!

If you find yourself in that situation, there’s probably little choice other than to keep on going. Drive as slowly as is safely possible and keep a close eye on your engine’s temperature gauge. If it starts going up into the red, pull over and switch the engine off for a while to allow it to cool. Should the situation require it, you should call for roadside assistance.

In the specific situation of 5W20 vs 5W30, putting the wrong oil would certainly have a negative effect – but it probably wouldn’t be an immediate worry. You should change the oil as soon as you can, but it wouldn’t be an emergency situation.

Putting 5W20 in when it should be 5W30 is likely to lead to a slightly hotter motor than usual. Putting 5W30 in when it should have been 5W20 could lead to a marginally warmer motor. Both of them could lead to mechanical parts and components wearing marginally more quickly than they would otherwise.

It would be more dangerous to put 5W20 in an engine designed for 5W30 than the other way around, but you shouldn’t do either.

No fret. Check your owner’s manual to make sure you’ve put the right oil in. If not, find a safe, level place to work, away from any drains, and change your oil. We will explain how to do this later on in the article.

What’s the History of Multi-Grade Oil?

In the past, cars had to have 2 oil changes per year. 1 at the start of winter, 1 at the start of summer.

There was a lot of oil changing going on. This was going on up until the 1960s.

You can read more about it on Addinol‘s website.

The invention of multi-grade oils meant that this was no longer necessary.

Are There Any Disadvantages to Multi-Grade Oil?

Compared to monograde oil… not really, no. Very few, at least.

Multi-grade oils don’t “hold” their viscosity for as long as a monograde oil. The oil ages faster, as well.

However, since it saves you changing your oil twice a year (and old oil should always be thrown away), these disadvantages are reasonably negligible.

The only exception might be if you live somewhere with a relatively constant year-round climate. In places like these, using a monograde oil may suit you better, as it will last longer. As always, consult your owner’s manual, local manufacturers and local mechanics – advice will vary depending on the car, too.

Why Do Cars Have Engine Oil?

5w20 vs 5w30 oil between metal

Motor oil is there as a lubricant.

Within your engine, there are many moving parts – the vast majority of them made of metals. As metals get hotter, they expand too. If this was to be left unchecked, eventually they would begin to hit one another. With the extreme forces found inside engines, this would result in major, likely irreparable damage.

Motor oil is there to prevent that. It essentially forms a barrier between 2 surfaces, absorbing the forces and keeping them as frictionless as physics allow. This is why it is important that the oil is as viscous as possible (but not so viscous that it can’t be pumped around the motor efficiently!).

Oil also has a role in the cooling department.

Although it’s not its primary purpose, the constant oil flow around the engine helps to regulate its temperature. Of course, the coolant is the main system responsible for this, and it does the majority of the work.

How To Change Your Motor Oil

Before changing your oil, you will need a few things. It’s also recommended to slightly warm your motor first, by running it for a few minutes. This will help the oil to flow through and drain out.

You should find a level surface, away from any drains. Any oil spills which leach into the public water system can carry some serious fines, not to mention be a serious pollutant and block up drains. (As an aside, this is also why you shouldn’t pour cooking oils and fats down the drain either – they block up the drains).

Anyway, coming back to it – yes, a level surface is very necessary, for 2 reasons.

  1. Safety – if you’re working under a car which isn’t on a level surface, it won’t be secure. This is a risk of serious injury or death, so always be careful. Always work safely.
  2. To actually allow the oil to drain – as the diagram shown below illustrates, if the sump isn’t flat, some oil will puddle in the corners and not drain out. This could be sludge, which is the sort of goo-looking-stuff your motor could develop over time, which clogs up the system. It’s basically the cholesterol of the automotive oil system. You want to make sure it’s all out, so make sure the car is flat.
5w30 vs 10w30 why car must be level
Diagram showing why motor oil must be drained from a car on a flat surface.

Note: It is often worth changing your oil filter at the same time as the motor oil. This is because you will need to drain the oil to change the filter anyway.

Equipment You Need

  • A 4-post or 2-post ramp (this makes the job easiest, if you have access to one. If not, 4 axle stands and an appropriate trolley jack are a must if your car doesn’t have much space underneath it).
  • The new oil and filter, in the correct quantity.
  • A funnel, for pouring the new oil in.
  • Rags, for cleaning.
  • An oil pan, for catching the waste oil.
  • PPE – gloves, especially.
  • A wrench or ratchet, to remove the sump plug.
  • A mid-range torque wrench (probably 3/8″). This is to reapply the sump plug to the correct level of torque.


  • Parts cleaner, also known as brake cleaner – this stuff is great for removing oil drip stains on metal.
  • A magnetic tray – to make sure you don’t lose the sump plug or washer.


  1. Make sure the ignition is off and the keys are well away from it.
  2. Remove the oil cap on the top of the motor. This will allow the oil to flow through the system more easily.
  3. Get underneath the car and put an oil pan in place, ready to catch the oil. Beware of the angle at which the oil will come out. It may surprise you.
    • If you can’t find the oil pan comfortably under the car, you’ll need to jack it up high. Make sure to do so safely and to put it on axle stands. Never spend long under the car yourself, to minimize any risk.
  4. Use the spanner or ratchet to remove the sump plug. It’ll be tight at first, but should loosen up fairly quickly. Once it’s loose, remove it and allow all the oil to drain into the pan.
    • Don’t be too harsh with it – the sump plug will be on pretty tight, but it should loosen up. The last thing you want to do is shear the bolt off. That’s a whole new level of problem.
    • The pressure of the oil inside the sump might push the sump plug out of place before you’re expecting it. To prevent this, you should keep pushing the sump plug in towards the sump while undoing it. When you’re ready, pull it away.
    • It’s very common to get oil all over your hand and wrist at this point. Make sure you move it away from the upcoming oil stream, instead of into it. If you do get oil on your hands, wait a minute before you change your gloves. Don’t stop watching the oil until it’s trickling. This is because the direction will change as the pressure in the sump gets less and less, as the oil drains out. After this, change your gloves – this reduces any dermatological risks.
  5. Once all the oil has drained out, replace the sump plug. Use the owner’s manual or an online website to check what the level of torque should be.
  6. You can now pour the exact quantity needed of new oil into the motor through the oil cap at the top, which should still be off. Make sure it’s the right oil multi-grade as well, as we looked at earlier in the article.
  7. Run the engine for a few moments. This fires up the oil pump and shoots the oil around the motor.
    • It might sound a bit scary for the first couple of seconds. Don’t worry – this is just the sound of the motor when there’s no oil in it. The oil should get pumped round soon enough, and the noise will go back to normal. If it doesn’t after 10 seconds, switch the engine off. There’s a big problem, probably with the oil pump. You will likely need assistance.
  8. Check the level on the dipstick. It should be between the minimum and maximum levels.
    • If it isn’t, just add more or drain more as required. No biggy.
  9. You’re all set. Clean up the car with rags and parts cleaner, and make sure to get rid of any spillages on the ground.
  10. Keep an eye on the dashboard lights and temperature gauge over the next 50 miles or so, and check the car for leaks when it’s parked up. Other than that, you’re good to go.

5W20 vs 5W30 Conclusion

We hope this article has been useful if you weren’t sure about the differences between 5W20 vs 5W30.

Motor oil is a vital part of the car and should be always be taken care of.

In short, the lesson to take away is to always trust your owner’s manual. The internet is full of weird and wonderful ideas which might be great… but might cost you a whole lot of money in the long-run as well.

Thank you for reading. Check back soon for more content.

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