engine oil

10w30 vs 10w40 Engine Oil – What’s the difference?

In Engine Oil by Magnus Sellén2 Comments

10w30 vs 10w40

Proper lubrication is necessary for all mechanical components of the vehicle to function smoothly.

Among the most commonly used motor oils are the 10w30 and 10w40. Although the difference between the two oils is not great, it is important to understand how they differ in viscosity.

In this article you will find information about the differences between the 10w30 and 10w40 engine oils, and you will get detailed information about engine oils that can be very useful when choosing the engine oil for your car.

10w30 vs 10w40 Differences

So what is the difference between these oils and which oil should I have for my car?

The short answer to this question is – 10w40 is a thicker oil than 10w30 at higher temperatures. 

But unfortunately, the answer is not so easy to really answer in a short sentence. To find out the real differences, you have to understand the basics of the parameters in the engine oil. So let’s continue with finding out what these numbers really tell us.

Understanding Oil Viscosity

engine oil

Viscosity is not just a physical term, and every automotive specialist knows the oil viscosity. Compared to water, oil is much thicker, i.e. if you pour water and oil at the same time, the water flows much faster compared to oil. This means that the oil is more viscous or has a higher viscosity than water.

Viscosity is a common term in connection with liquids and is influenced by several factors including temperature. For example, if a bottle of oil remains in the refrigerator for a long period of time, it can turn into a solid wax-like material. The relationship between the viscosity of the oil and the temperature is inversely proportional. When the temperature is increased, the viscosity of the oil decreases and vice versa.

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The engine and other internal components need engine oil for effective operation, and the oil should be able to handle different temperature variations. For example, if the engine generates extreme heat, the oil should not become too thin, as it will no longer protect the internal components. Similarly, when the engine is cold, the oil should not be so thick that it cannot flow evenly inside.

To learn more about oil viscosity, it is important to understand how each oil is named and graded.

Deciphering the Oil Grade

The start number of both oils is the same and is ’10’. This indicates how easily the oil can be filled in at low temperatures, typically during the winter season. The lower this number is, the easier it flows in cold weather. An oil that starts with ‘5’ will, therefore, pour faster than the oil with the number ’10’.

The W stands for “winter” and specifies that the first number is given at winter temperature. The last number indicates how easily the oil can flow at the optimal engine temperature or during the typically hot summer season. The higher this number is, the better the oil protects the engine components under extreme pressure and heat.

Here is a detailed video if you want to learn more about the different types of oil:

Should my car have 10w30 or 10w40?

The best way to find out which oil to use is to consult the owner’s manual of your car. The manufacturer usually specifies a range of oil viscosities that are best suited to the engine of your car.

The 10w30 engine oil works best if you live in colder regions, as the heat from the outside is not too great and the only heat acting on the engine is the heat generated by the engine itself.

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However, if you live in a hotter region, we recommend that you choose 10w40 engine oil.

In areas with a warm climate, both the heat generated by the engine and the heat from the sun will affect the engine. You can still use 10w30 engine oil, but it dilutes much faster and damages the internal components of the engine. The 10w40 engine oil will do a much better job by providing sufficient lubrication and protecting the metal components.

Again, the best way to find out is to either refer to the owner’s manual or call your dealer. Remember that automakers have invested millions of dollars in research to build and optimize your engine. They have probably done thousands of tests in both cold and hot conditions, and if you follow their oil guidelines for your engine, you will probably get the best results.

Which brand of the engine oil should I use for my car?

This is another question that cannot be answered quickly, and you will probably get 10 different answers if you ask 10 people. There are so many parameters about the engine oil to consider before you choose your engine oil. Again, refer to your owner’s manual and follow their guidelines. You have spent a lot of research and money to select the right engine oil for your engine under your conditions.

I do not recommend not choosing a cheap oil just because of the price. The engine oil is a very cheap option, but poor-quality engine oil can cause major damage inside your engine. Choose some of the big brands like Castrol or Liqui Moly.

Should I use thicker oil in my old car?

There is a widespread misunderstanding among people that as your engine gets older, you should replace the current engine oil with a higher viscosity engine oil. This was true for old vehicles, as over time the oil flow through friction expanded and the choice of a thicker oil seemed a sensible option.

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In modern vehicles, however, these oil channels remain the same size throughout the life of the engine. The use of a higher-viscosity oil may not be beneficial as it can cause damage to internal parts.

Now that you have all the important information about the engine oil and viscosity level, you can easily distinguish between the 10w30 and 10w40 engine oil. However, if you are still not sure, you can consult your car’s owner’s manual or the car manufacturer for more information.

If you have further questions about the car, you can leave a comment below and I will answer these questions as soon as possible.

Hello I'm Magnus, the owner and the writer of this website. I have been working with cars since I was 16 and I'm specialized with in-depth Automotive diagnostics. Also been driving drifting for the last 6 years. I'm here to give you answers to all your automotive questions and I hope that you enjoy our content.

2 thoughts on “ 10w30 vs 10w40 Engine Oil – What’s the difference? ”

Comments
  1. hello, i live in a country with a tropical climate with more warm temperatures and drive a lexus is250 which has about 80.000 km on it. so my question is if i can use the 10w40, 5w40 instead of the 10w30. at this point i am using the 10w30 but the oil after 3000 km gets black smells a little burned. so any advice what to use because i read the last piece of your article about the new engines types how the oil passages through the engine

  2. in owners manual it recommends 10w30 engine oil.
    our climate is ranging 32 – 37 degreescelcius.i’m really confuse if i’ll use 10w40 to match the outside temp. or follow the manual.
    advice pls.
    thanks

  3. Due to a very high demand and high ammount of comments, you have to wait for some time for your car questions to get answered. If you want to get fast answers from a certified master technician you can ask your questions here:
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