Can I use 10w40 instead of 5w30 in a car?

10w40 instead of 5w30 Oil

Technically speaking, 5w-30 engine oil can be replaced with 10w-40 engine oil. But we don’t recommend it and here’s why.

Do not use 10w-40 instead of 5w-30

Yes, we know that every auto mechanic can have a different opinion on this. But let’s try to get to the bottom of this issue.

Everyone knows that engine oil, in addition to its main task – to lubricate engine parts, to minimize its wear – has a number of other functions. The additives that are added to the oil, are able to prevent oxidation and corrosion, and clean from soot deposits and small chips.

Manufacturers always recommend using a particular oil for their vehicles to improve their performance in the operating environment. However, some car owners use non-recommended motor oils for different makes and models of cars at their discretion.

5w30 vs 10w40 Motor Oil

As a car enthusiast or mechanic, you should understand that 10w40 and 5w30 oils have two different viscosities. The whole difference is the viscosity levels almost entirely determine their use in car models.

Oil viscosity refers to the density of the fluid and is measured using water as the standard viscosity level. This means that any fluid can have a higher or lower viscosity than water. In addition, the thickness or viscosity is known as the weight of the fluid. Two numbers define the viscosity of engine oil when naming it.

  • Castrol Edge 5W-30 Advanced Full Synthetic Motor Oil
  • Amsoil Signature Series 5W-30 Synthetic Motor Oil
  • Idemitsu Full Synthetic 5W-30 Engine Oil
  • Mobil 1 Extended Performance 5W-30
  • Shell Rotella Gas Truck 5W-30
  • Red Line Motor Oil 5W-30
  • Castrol GTX 10W-40 Motor Oil
  • Red Line Synthetic Motor Oil 10W40
  • Pennzoil High Mileage Conventional 10W-40
  • Valvoline High Mileage 10W-40
  • Pennzoil Conventional 10W-40
  • Quaker State Conventional Motor Oil 10W-40

What does viscosity denote?

  • The first number refers to viscosity at low temperatures, and the second number, which comes after “w”, refers to the viscosity level at higher or warmer temperatures.
  • The letter “w” also refers to winter or low temperature. For example, 10w40 with a higher viscosity level is thicker and heavier than 5w30.

How does viscosity affect vehicle performance?

The viscosity and thickness of any engine oil are always a compromise. This is because not every part of the car, especially the engine, requires the same level of thickness or viscosity. Some parts of the car need a thinner film to protect it from external influences, while others need a thicker film.

Both liquid and thick engine oil are needed for optimal performance of the car. But you can’t use two different car engine oils at the same time. So it’s best if you can find a brand of motor oil that has the best balance between the recommended thickness and thinness of the oil.

Why do people use different types of oil?

Engine oil cost

10w40 motor oil is much cheaper than 5w30. That’s why some car owners try to save on the cost of motor oil.

Reduce oil consumption

10w40 oil is thicker than 5w30 oil, so it’s used to reduce oil consumption.

We’ve seen many car owners swap out their 5w30 engine oil for 10w40 engine oil. So it’s not surprising that many people ask, can I use 10w40 instead of 5w30?

What is better for an engine 5w30 or 10w40?

Most 5W-40 oils, are synthetic oils and are recommended for use in newer engines, as such engines are demanding not only the viscosity of oils but also their composition. The 5W-40 is inferior in viscosity, due to the reduced winter coefficient. The car will start better in wintertime. But when reaching operating temperature, the oils give exactly the same protection.

10W-40 is recommended for cars that have more than 150,000 miles and is often a conventional oil. There are some fully synthetic 10w40 viscosity motor oils on the market, but their cost is quite high and their use is not always paid for.

If we talk about the viscosity of the oil, 10W-40 is a bit thicker than 5W-30.

Which oil is better?

The best oil for your engine is the one specified by the manufacturer. For older engines, 10W-40 is better. It, due to its higher viscosity, will reduce oil consumption. For newer engines, it is better to use 5w.

What oil is better for summer conditions?

The 5w40 oil most often has a higher viscosity index (it doesn’t change viscosity so much when the temperature changes) than the 10w40, so it has higher viscosity at high temperatures. And these temperatures are present on the cylinder walls and on the exhaust valve stems. Therefore it protects better than 10w40 these parts working under extremely adverse conditions, especially in the summer heat.

Can these oils be mixed?

It is possible to mix these oils, but they should not be abused. And if you mix them, you should choose oils of the same manufacturer. When you mix oils, you can lower or raise the viscosity, depending on the amount of oil of the same brand. You also have to consider the composition of the oil.

Everyone makes his or her choice, based on what he or she is pursuing and what he or she wants to get from the engine oil and from the car as a whole.

What is Engine Oil 10w40?

It is a base engine oil. At higher temperatures or when the engine is warm, its viscosity level is 40, and at normal or lower temperatures its viscosity level is rated as 10. Thus, 10w40 motor oil is preferred at higher temperatures because its viscosity at low temperatures is quite high.

What Is 5w30 Motor Oil?

5w30 is synthetic motor oil. However, judging by its number, it is much thinner than 10w40. We also get from the number that 5w10 has a viscosity index of only 5 at low temperatures, which is half the viscosity of 10w40 at low temperatures.

Conversely, at higher temperatures, 5w30 has a viscosity rating of 30, which is also less than 10w40.

What is the difference between 5w30 and 10w40 oil?

After considering the characteristics of oils, and understanding the markings and classifications, it is possible to draw conclusions and conclusions.

The difference between 5w30 and 10w40:

  1. In the temperature range of winter use, 5W is a more “winter” oil, but it also happens that 10W from some manufacturers withstands lower frosts than 5W from others. Everything is relative, look not only at the SAE but also directly at the yield point and dynamic viscosity.
  2. The difference in viscosity at operating temperature. And now this is important. If it is recommended to pour only 5w-30 into your car, you should not pour 10w-40, and vice versa. You can see with your own eyes how different the viscosity of these oils is after engine warm-up.
  3. Important difference: 5w30 is most often synthetic, 10w40 – conventional oil, but the opposite happens, but very rarely.
  4. Price: 5w30 is more expensive, 10w40 is cheaper.


In new engines with up to 100,000 miles, 5w30 is recommended. After 100,000 miles, it is wise to change to 10w40. But when choosing the viscosity, be guided not only by the mileage of your car, but also by the recommendations of the engine manufacturer.

What viscosity to choose?

Having all the above information, the choice is up to you. The main thing is to provide a smooth start of the engine, which will increase its service life.

We will summarize, when and what viscosity to choose:

  • High mileage – 10w40, engine new – 5w30, but first of all we look at the recommendation of the engine manufacturer.
  • For northern regions, low winter temperatures better suit 5w30, but it all depends on the loss of fluidity temperature and the dynamic viscosity of a particular oil brand.
  • Operating conditions. Oils with the same high-temperature index SAE may have slightly different viscosity within the limits set by the standard. Thinner oils give you fuel economy, thicker oils give you more protection. If you have close to the sports driving style, it is better to choose thicker oils, but within the limits of SAE viscosity recommended by the automobile manufacturer.


Before choosing an oil, check the car’s manual, it is necessary to use the one recommended by the manufacturer.

The difference between 5w30 and 10w40

Judged by their viscosity, 5w30 tends to be more liquid and better suited for cold weather use.

Conversely, 10w40 is a higher viscosity oil designed for warmer conditions.

With its lower viscosity, 5w30 flows better at low temperatures. Thus, it protects various parts of your car’s engine in colder temperatures. It’s best when starting the car, as the internal temperature of the engine is relatively low at this time when starting.

A 10w40 oil with a higher viscosity protects engine parts better at higher temperatures or when the car is running at full speed.

But these numbers can sometimes be misleading. For example, 5w30 is not always recommended at low temperatures and not for all car models. Also, not all cars in hot regions use 10w40.

So it’s always best to go by the manual and use what your car manufacturer suggests.

Can I use 10w40 instead of 5w30?

Our verdict:

We believe that you should never use 10w40 instead of 5w30.

Since these oils are designed to work under different conditions, so they function differently. If you use 10w40 instead of 5w30, it won’t perform as well as 5w30 at low temperatures.

Therefore, your car may experience a certain amount of inconsistency.

Also, with a higher viscosity, it will have a lower flow rate. Thus, your car may not reach the desired vehicle speed. In addition, it will cause wear and tear on the engine parts.

You should not use 5w30 instead of 10w40, especially in warmer conditions. The only recommended use of 5w30 is when temperatures are exceptionally low or freezing.

But you can also bypass such conditions with 10w40, as it continues to provide good performance even at 32°F.

My friends and I created this site to tell you a lot of useful things from the world of cars. I worked as a salesman in a big auto parts store and gained a lot of experience in this field, now I am sharing my experience with you.

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