[Detailed] Can I Use 10w40 Instead Of 5w30 +Other FAQs

Manufacturers always recommend using a particular oil for their automobiles to boost their performance in all conditions. The same is true for lubricants or power steering fluid. Yet, many car owners and even quite a good number of motor mechanics will use non-recommended motor oils for different car brands and models.

One such case is with 10w40 and 5w30. We have seen many car owners interchanging between 5w30 motor oil and 10w40 motor oil. So Can I use 10w40 instead of 5w30?

Technically speaking, 5w10 graded motor oil is replaceable with 10w40 motor oil. But it is not recommended and won’t bring any substantial performance boost to your car’s performance and lifespan.

Also, both these motor oil feature different viscosity levels and are suitable for working under different temperatures. So, using one in place of another isn’t practical either. But for this, firstly, you have to understand the relation of viscosity of motor oil with its performance in different situations.

10w40 Instead Of 5w30

Does viscosity in oil matter much?

As a car buff or mechanic, you should understand that both 10w40 and 5w30 graded oil have two different oil viscosities. The difference in their viscosity level almost entirely defines their applications in car models’.

But what is the viscosity of motor oils? and, why does it matter?

To answer it shortly, viscosity refers to the thickness of any liquid and is measured with water as the standard viscosity level. It means any liquid might have a higher or lower viscosity number compared to water. Also, the thickness or viscosity is known as the weight of the liquid. Two numbers define the viscosity of motor oil at their naming.

The first number refers to viscosity at low temperature and the second number, which sits after “w,” refers to the viscosity level at a higher or warm temperature. Also, the letter “w” refers to winter or low temperature. For instance, 10w40 with a higher viscosity level is thicker and weightier than 5w30.

Read also >> Is it ok to use 10w40 instead of 10w30? Does it affect performance?

how does viscosity affects car performance?

First off, the viscosity and thickness of any motor oil are a tradeoff. It is because not every part of the car, especially the engine, requires the same level of thickness or viscosity. Some car parts will need a thinner film to protect against external elements, while others will need thicker films.

For instance-

  • Piston and cooling nozzles require increased oil flow. Applying thicker oil such as 10w40 on these parts will slow down the flow speed. So, they won’t be able to cool off the engine parts effectively. Car manufacturers, therefore, recommend using a thinner oil in cooling nozzles and pistons to improve its flow rate so that it can cool down the parts better.
  • On the contrary, different bearings and rods in the car will go through constant wear and tear due to abrasion and external elements. So, the thicker the protective film will be, the better it will be for these parts. So, thicker oil is preferable to protect these car parts.

It should be clear that a car needs both thin and thick motor oil for optimal performance. But you can’t apply two different motor oils for the cars simultaneously. So, it would be best if you found a motor oil grade that has the best balance between the recommended oil thickness and thinness.

The manufacturers thus choose a good thumb or rule-

First, they measure the parts that need higher viscosity and the parts that need lower viscosity oil. Then, after calculation, they choose the motor oil that has the least tradeoff so that your car gets the maximum profit.

It simply implies that choosing motor oil other than manufacturers’ recommended cars increases its chance of damaging parts. And when it happens, you need to replace the part, and car parts aren’t cheap.

So, when you use non-recommended oil for a car with higher or lower viscosity, you run the risk of choosing the highest tradeoff.

What Is 10w40 Motor Oil?

It is synthetic motor oil. Ata higher temperature or when the engine is warm, its viscosity level is at 40, and at normal or low temperature, the thickness level is rated at 10. Thus, 10w40 motor oil is preferable at a higher temperature since its viscosity at a low temperature is pretty high.

What is 5w10 Motor oil?

5w30, too is synthetic motor oil. However, as its number suggests, it is much thinner than 10w40. Also, from the number, we get that at low temperature, 5w10 has a viscosity rating of only 5, which is half the viscosity of 10w40 at low temperature.

On the contrary, at a higher temperature, 5w30 has a viscosity rating of 30, which is also fewer than 10w40.

what is the Difference between 5w30 and 10w40?

As their numbers suggest, in general, 5w10 is thinner and better for use in cold weather. On the contrary, 10w40 with its higher viscosity is designed for warmer conditions.

  • With lower viscosity, 5w10 flows better in low temperatures. So, it will protect the different parts of your car’s engine at a lower temperature. It suits better when you start the car as, during this time, the engine’s internal heat is relatively low.
  • 10w40 with higher viscosity will protect the engine parts better in warmer temperatures or when the car is running at full speed.

But, these numbers can be confusing and tricky. For instance, 5w30 isn’t always recommended in low temperatures for all car models. Similarly, not all cars in the tropical regions use 10w40. Instead, it is always better to go by the book. So, use what your car manufacturer suggests.

Read also >> Difference Between 75w90 And 80w90: (5 Key Differences)

What happens if you put 10W40 oil instead of 5W30?

What happens if you put 10W40 oil instead of 5W30

You should never use 10w40 instead of 5w30. Both motor oils are designed to work in different conditions, so they function differently. If you use 10w40 in place of 5w30, it won’t perform as well as 5w30 in low temperatures. So, your car may experience inconsistency.

Also, with higher viscosity, it will have a decreased flow rate. So, your car may not reach the desired car speed. Also, it will cause wear and tear of the engine parts.

Also, you shouldn’t use 5w30 in place of 10w40,especially in warmer conditions. The only recommended use of 5w30 is when the temperature is exceptionally cool or freezing. But you can also bypass such conditions with 10w40 as it continues to deliver good performance even at 32°F temperature.

So, long story short-

Use 10w40 for those cars which accept it. And use 5w30 for those cars that accept it. It may be harmful to your car and the engine.

people also ask (FAQs)

1. Is 5w30 better for fuel economy?

5w30 is thinner than 10w40. So, it will face less friction with the engine parts and get a boost in fuel efficiency. But its thinner properties aren’t good to stop the engine parts from wear and tear. Thus, you have to choose between the increased fuel efficiency and the cost of wear and tear for the engine parts while opting for 5w30.

2. Is 10w40 good for cars with higher mileage?

When you have driven your car for an extended period, its engine will have more wear.  As the engine is worn out and hotter, 10w40 with its higher viscosity offers better lubrication. So, you can expect an improved mileage with it in hotter temperatures.

closing thoughts:

Here we will end our discussion, You should never use 10w40 instead of 5w30 unless your car accepts the motor oil. It is always best to follow the user manual for the optimal performance of your car and its engine.

The manufacturer chooses and recommends motor oil grade for your car after a lot of research. So, following it will be your best bet even if mechanics recommend applying other motor oils. The last thing you won’t want is a damaged engine that needs a replacement for applying non-recommended motor oil by breaching the user manual.

It will cost you dearly.

Who Worked on This?



I'm the guy responsible for ensuring that every blog post we publish is helpful for our reader.

Mahir Ahmed


I'm the guy responsible for ensuring honest, informative, accurate and helpful guide to the reader.

Leave a Comment