5W30 vs 10W30

5W30 vs 10W30 – Which Engine Oil Should I Use?

In this article, we will be comparing 2 different engine multi-grade oils: specifically, 5W30 vs 10W30.

If you’re new to the terminology surrounding the oils used for cars, don’t worry. It’s not as complicated as it might look. As we go through the explanation today, we’ll think about a few things:

To jump to any section, in particular, feel free to click on one of the links above.

Otherwise, let’s jump into it.

5W30 vs 10W30 – What Do the Numbers Mean?

5W30 vs 10W30? What’s the difference? And what’s all the fuss about?

Here, we are thinking about multi-grade oils.

Mechanical multi-grade oils are always written in the following format, as you’ll have seen:

  1. Number
  2. “W”
  3. Number.

These numbers refer to the relative viscosity of the oil. We will explain viscosity in more detail in the next section of this article. This multi-grade system was developed and implemented by the Society of Automotive Engineers.

It is referred to as a “multi-grade” system because, well, there is more than 1 grade of oil. At different temperatures, the engine oil behaves differently.

All cars are designed to use a certain type of oil. If you open your owner’s manual (which is absolutely vital whenever you’re doing any work with your vehicle), it will tell you which engine oil you should be using. Almost every car in the world will require a multi-grade oil of some kind.

Most manufacturers also include a “manufacturers recommendation”, or something along those lines. If you have a new car, it’s important to use the exact producer and grade that they say – otherwise, you could void the warranty.

The majority of cars will run fine on any one of 2 or 3 similarly-graded oils, but you should always use the recommended one and follow what the owner’s manual says.

Although we will usually be talking about engine oil, other oils (such as gearbox oil) use the same kind of specification. We will explain a little more about gearbox oil later on in the article.

What is Viscosity?

As mentioned in the previous section, the numbers in oil gradings represent the level of viscosity. For example, in “5W30”, we are looking at the “5” and the “30”.

So, what is viscosity?

The best way to think of it is “thickness” – how “thick” the liquid is.

The more viscous a liquid is (in this case, automotive oils), the “thicker” it is. The “thicker” it is, the slower it will flow in its natural state.

Check out the official definition from Encyclopedia Britannica. Technically, viscosity is a measure of the amount of internal friction resisting its own flow. You could, therefore, also think of it as meaning “how much the oil slows itself down”.

The higher the number is on your engine oil, the more viscous it is. The “thicker” it is, if you like.

So, now we know what the numbers represent, but what’s the “W” about? To explain that, we need to take a quick dip into the bay of physics…

What Does the “W” Mean?

Let’s start by giving you the answer, before explaining it. The “W” stands for “winter”.

The first number in your multi-grade engine oil grade refers to its viscosity in winter. The second number refers to the oil’s viscosity at is operating temperature of 100c.

For example, let’s dissect what “5W30” means.

  • “5W” – the oil has a relative viscosity of “5” in “winter”, which means it will flow quite easily in cold temperatures.
  • “30” – in operating temperature (100C), this is how viscous (how “thick”) the engine oil is.

By contrast, 10W30 is slightly more viscous in cold temperatures but runs at the same viscosity under normal temperatures.

So, why do we use multi-grade engine oil? That is, why do we use oils that specifically have a higher viscosity when hot, and lower when cold?

It’s because natural oil becomes less viscous when heat is added. You can think of it as being “thick” when cold and “thin” when hot, in its natural state.

In terms of cars, this isn’t what we want.

Think about it.

  • When you start your car, the oil pump starts up and begins sending oil around your engine. Everything is cold and just starting to warm up. You have to get oil around the engine as quickly and efficiently as possible. That’s quite hard to do if the oil is thick and doesn’t flow easily.
  • Likewise, when the engine is up to temperature, you would have the opposite problem. The oil is there to provide lubrication between moving mechanical parts – it’s essentially just a slippy surface in between 2 hard ones, preventing friction between them. The thinner the oil is, the less good it would be at doing this.

To get around these problems, we use synthetic multi-grade engine oils. These are designed and created to be thin at low temperatures (helping the car to start) and thicken at normal operating temperatures (allowing for sufficient lubrication in the engine).

5W30 vs 10W30 – How Do They Compare?

When thinking about 5W30 vs 10W30, it’s important to realize that they are very similar. In fact, as we discussed above, the only real difference is to do with cold-weather viscosity.

10W30 oil will be slightly more viscous in “winter” conditions – when the engine is cold. This means that, on cold days, the car will be under marginally more strain when the engine is starting.

You should take “marginal” as the keyword there, though. Although it does make a slight difference, it’s minimal and unlikely to affect you, unless you live in arctic conditions.

Let’s get something out there, as well. Unlike what many click-baiting articles would have you believe, there is no such thing as “the best engine oil”. Every oil is made for a specific purpose. Your car is built with an oil specification in mind. Never trust a random blog article more than your owner’s manual.

5W30 and 10W30 will probably both work in your car, but to know which you should use, simply consult your owner’s manual. If you have lost that, you could either

  • take your car to the local auto shop and ask them to find out for you – or,
  • check on one of many vehicle statistics databases on the internet.

There may be a small fee for either of these methods, but it shouldn’t be more than $10 or $15.

Many cars will happily run on both oils. It will also vary within a manufacturer’s range, from model to model, depending mostly on the engine size and the geographical selling locations. For example, cars in Alaska are more likely to have lower winter-grade ratings for the oil than cars sold in Texas.

5W30 vs 10W30 – Why Are There So Many Different Types of Engine Oil?

Although many cars use either 5W30 or 10W30, some newer cars are heading towards lower oil viscosity ratings. For example, 0W20 oil is no longer an uncommon sight.

In the past, engines tended to be built with higher viscosity levels in mind. This can be thought of as due to the bigger, less polar-bear-friendly V8s of days gone by. These monsters relied on huge, heavy powertrains and internal components, meaning that more lubrication was necessary when they were running. For example, if you have a Ford Mustang from the ’60s, it probably runs on 10W30 or 10W40.

It also wouldn’t be unusual to see modern diesel trucks running on high-grade oil such as 15W-40.

All of these beg the question, why are there so many different types of engine oil?

Well, as previously alluded to, it all boils down to a few different factors, including the following.

  • The size and power of the engine (and how much friction it produces as a result).
  • The geographical climate for the region the car is sold in (in short – hot, warm, or cold?)
  • The temperature range the engine internals are expected to go through.
  • The regional availability for the type of oil required.

All cars are built for oil rated to a certain SAE specification. It’s important to use the right one because otherwise it wouldn’t be able to do its job properly. The oil is a critical part of the engine, as the following YouTube video from Castrol explains.

5W30 vs 10W30 – What Would Happen If I Used the Wrong Engine Oil?

If you live in an area with a moderate climate, the answer is – probably not much.

Although it’s not recommended, the majority of cars will get away with a variation of 5 for each number. It would often be okay to replace 5W30 with 0W25 or 10W30, for example. However, we wouldn’t recommend this in most situations, just in case.

Using oil with dramatically different numbers is another thing altogether.

If your car was built for 0W20 and you put 15W40 in it, make sure you change the oil out as soon as possible, replacing it with the correct specification. Not doing this is likely to result in the following 2 problems.

  1. You will have difficulty starting the car and getting it running, especially on cold mornings. Following on from above, this would be because the cold oil is too thick to get around the engine quickly.
  2. When the engine is running, the oil may not lubricate the parts efficiently enough, leading to the engine overheating and, in serious cases, seizing up. In the example mentioned above, the viscosity of the oil is too high, and so it wouldn’t be getting around the engine quickly enough.

Basically, stick to the owner’s manual, not some random blog or YouTube video you find. It’s for the best.

If your car is having trouble with starting on cold mornings, it could be related to the electrical ignition system. This involves the battery, the alternator, and the starter motor, as well as all the related wiring. On that note, click here to check out our articles on White Smoke From Engine – What Might Be Causing It? and Car Won’t Turn Over.

What’s the History of Multi-Grade Oil?

Multi-grade oil has been around for the last 50 years or so.

It was invented because, in the past, people often had to use a “thick” oil in summer and a “thin” one in winter, meaning 2 oil changes per year.

The introduction of certain polymers into the oils leads to these multi-grade oils. It removed the issue of having to change your oil twice a year and therefore led to cars being easier to maintain. Read more about the history of multi-grade oil here on transdiesel.com. It also includes a very useful table you can check out.

Nowadays, multi-grade oil is classified by 4 separate viscosity tests, 2 measurings at “W” (winter) temperatures and 2 measurings at (100c) operating temperature.

The winter tests check the Low-Temperature Cranking Viscosity and the Low-Temperature Pumping Viscosity. These make sure that the oil isn’t too thick for both the starter motor and the oil pump, respectively.

The first operating temperature test checks the viscosity at 100 degrees Celcius, where the oil must fall within a certain range. The second is called the HTHS (High Temperature/High Shear) test, where the oil is heated to 150 degrees Celcius and then shear forces are applied to it. This mimics some of the surfaces, components, and positions that the oil will have to lubricate in the engine.

Once these tests have been done, the oil gets its official SAE grading.

Why Do Cars Have Engine Oil?

As mentioned above, it’s primarily for lubrication. Engine oil helps to remove friction from inside the engine, keeping everything ticking over smoothly. This stops heat from building up within the components.

5w30 vs 10w30 oil between metal

Its secondary purpose is direct heat removal, although it’s not directly responsible for this task. The aptly-named coolant system is what has the main job of getting all the excess heat out of the engine.

If internal combustion engines didn’t have engine oil, they would, in laymen’s terms, break. Technically, they would either seize or self-destruct, as the excess heat caused by friction would lead to the metals within the engine unit becoming warped. Once this has happened, it’s game over for it, and you’ll need a completely new one.

How To Change Your Engine Oil

If you aren’t sure about how to change your oil, we recommend taking your car to a professional.

Here are the basic steps required to perform it yourself.

Before you start, you will need (as a minimum) the following:

  • Your new oil and oil filter (check the specification and amount).
  • Socket or hex key (also known as “Allan key”) for the sump plug, along with the ratchet.
  • Pan or tray to catch the waste oil.
  • Funnel to put the new oil in.
  • A medium torque wrench for torquing up the sump plug.
  • Granules or other clean-up kits, in case of any oil spills.
  • PPE.

Steps

Park the car on a level surface with the parking brake on. Run the engine for 5 minutes, before switching it off and removing the key from the ignition. This means that the oil will flow out more easily, but make sure it is not hot.

Don’t start anything until the engine is off.

If your vehicle is particularly low, you may need to borrow a small ramp from a local garage or friend. Jacking the car up to change the oil will only work if you place axle stands under, so the car remains level. Always be careful and safe when working under cars. If in any doubt, it’s better to be safe than sorry.

The car needs to be level so that the oil can collect in the sump to drain out efficiently. If it’s not level, some oil may not drip out, as demonstrated in the diagram.

5w30 vs 10w30 why car must be level

Open the oil cap at the top of the engine. This leads to airflow through the system, from top to bottom, helping the oil on its way out. Put the oil tray underneath the sump plug and then remove it, being careful to damage or lose the sump plug

The oil will then drain into the pan. Leave it for 10 minutes or so, but don’t stop watching it. As the flow rate decreases, the angle of the oil coming out will change, and so you will have to constantly move the oil pan to make sure you don’t make a mess on the floor.

It’s also worth noting that there are heavy fines for polluting the drains with oil or any other toxic substance, so make sure not to.

Once all the oil has drained, put the sump plug back in and use a torque wrench to tighten it to the correct amount. Swap out the oil filter.

Then, drop your new oil in through the open oil cap. Make sure you put the right amount in. You can find all this information in the owner’s manual.

After that, replace the cap until it clicks on. You should then start the engine. For the first couple of seconds, it might make a couple of scary sounds. This is because the oil is all in the sump – it hasn’t been pushed around the system yet. After a couple of seconds have passed, it should go back to sounding normal.

If everything has gone okay, great. Make sure you check for any leaks by leaving the car parked up for a while and coming back to it after a few hours. Make sure you check the oil level is correct before test driving and check it again after.

Dispose of the oil legally – this may involve calling someone up to come and take it off your hands.

What About Gearbox Oil?

10-Speed Automatic

As mentioned earlier, here is a brief section on gearbox oil.

Gearbox oil is, to me, the worst smelling thing ever. I absolutely can’t stand it. And the worst thing is if you get it on your skin and have to deal with the smell for the next 2 weeks. Call me a baby, you’d be right, but I can’t stand it. I always double glove and cover my wrists when working with the stuff.

Anyway, gearbox oil is also multi-grade, but it’s usually much more viscous than engine oil. This is because there is much more going on within a smaller space. Lots of components are moving and meshing with each other all the time, and so it requires thicker oil.

A typical gearbox oil might be 75W140. You can see how that is much higher than your typical engine oil.

It can help to visualize it, to some extent. Imagine a thin, runny liquid passing by hot metal, and then a thick one. You can see that thicker oils are required to keep the friction levels down.

Read more about gearbox oils on total.co.uk here.

The above video is a promotional clip from Shell, nicely explaining why you need to make sure to look after your gearbox oil.

Conclusion

Comparing 5W30 vs 10W30 is pretty basic, fundamentally. There is very little difference between the two, apart from 5W30 being slightly thinner when cold.

You will probably be fine with either oil in your car but, as always, follow the manufacturer’s advice. Everything has been designed to be as safe and secure as possible, and also modified to your typical national climate.

If you’re experiencing a freak weather situation (such as a snowstorm here in England – not something that we see very often!), it’s certainly not worth changing your oil for a few days, although there’s nothing to stop you if you wanted to. You might just have to treat the car gently over the next few mornings.

In conclusion, if you’re wondering whether to use 5W30 or 10W30, go with what your owner’s manual suggests. Otherwise, we hope this article has been useful for explaining the differences between these oils.

Check back regularly for more content.

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