Can I Use 10W40 Instead Of 10W30?


Any lubricant is as essential for the engine as the blood in the human body. It prevents the engine components from grating roughly with each other.

Grating causes wear and tear in engine components, that accumulate in the base of the engine as well in crankshaft called debris. If you don’t use any good and proper lubricant, these debris particles can seize your engine.

We use good quality engine oil (motor oil) as a lubricant in our engines to protect them from wearing and tearing.

Generally, every vehicle comes with an owners’ manual, in which there is a proper guideline regarding the choice of engine oil that suits your engine best. There is a wide range of engine oil available in the market regarding its viscosities. 0W-20, 5W-20, 5W-30, 10W-30, and 10W-40 are some commonly available viscosities in engine oil.

But the question is: Can I use 10W40 instead of 10W30 in my car’s engine? There are many things to understand to clear this concept.

What does the viscosity index of motor oil mean?

Viscosity index is simply a viscosity range of any fluid that relates its changes in viscosity to the relative temperature changes.

Since engine oils are needed to lubricate different parts of the engine, they also need to be able to withstand engine temperature fluctuations. This means that if the engine is cold, the engine oil should not increase its viscosity too much so that it can no longer move efficiently in the engine (remember that a cold temperature means more viscous oil or thicker). This can lead to excessive oil temperatures while increasing friction.

On the other hand, since the engine is already running and generating enormous heat, the engine oil should also not be too thin or less viscous than it should, as it has a similar viscosity to that of water. If this happens, the engine oil will no longer be able to protect critical engine parts from overheating because the oil is too liquid. This means that the different moving parts of the engine will rub against each other without any protection.

This is why the engine oil viscosity index is a very important parameter to protect your engine. In general, the higher the viscosity index, the more stable its viscosity in these temperature changes, and the more the spectrum range here, the better is the engine oil.

XW-YY – What do these numbers mean?

Probably you must have seen these SAE viscosity index numbers on almost every canister of engine oil.

Years back, there is only single graded motor oils, whose performance was low as compared to now modern multi-graded viscosity index motor oil. All of these multi-graded engine oils are now available in every kind of engine oil, i.e., conventional oil, synthetic oil, synthetic blend oil, and high-mileage engine oil.

The first number represents the viscosity of engine oil at a lower temperature. The lower the number here, the higher its ability to maintain its optimum viscosity at a lower temperature (while starting the engine). This means it would not become so much viscous/thick that hurdle its ability to keep flowing in the engine.

“W” stands for winter, which relates its lower viscosity to winter.

The second number after “W” represents the viscosity of it at a higher temperature (i.e., at the running condition of the engine). The higher the number here, the higher its ability to maintain its optimum viscosity at the operating temperature of the engine. This means it would not become too thin, which causes wear in the engine due to depletion in viscosity.

10W30 vs 10W40 – Difference

The main difference between both oils is their viscosity index. The lower viscosity of both oils is 10. It means that at lower temperatures both oil show the same behavior.

The oil with lower viscosity of 10 considers good for the areas where the average temperature in the whole year remains medium to a lower extent. But not good for an extremely cold climate, where the average annual temperature remains below the 0°C.

So what is the difference between both oils?

The main difference between both oils is their upper viscosity, which is 30 and 40.

As discussed above, the higher the number here, the more its ability to perform better at the operating temperature of the engine. Thus 10W40 oil performs better than 10W30. It resists more to get thin at engine operating temperature and maintains its viscosity at the optimum level to provide better lubrication between engine moving parts and lessen the wear and tear between moving parts.

Can I use 10W40 instead of 10W30?

The areas where the average weather temperature is higher would better to use 10W40 oil in their engines than 10W30. But we would recommend you it’s better to consult your owners’ manual to check the recommended engine oil according to the prevailing weather temperature in your area.

The 10W-30 synthetic oil range is -25°C / -13°F to 30°C / 86°F (sometimes -30°C / -22°F to 35°C / 95°F) while that of 10W-40 is -30°C / -22°F to 40°C /104°F.

So check the climatic condition in your area, and choose the best-branded engine oil according to the recommendation, also displaying the starburst symbols confirming that it is an API tested engine oil.


See Also: How Often To Change Engine Oil?

Factors affecting choosing a better engine oil.

The following factors should be taken under consideration when you’re deciding to use one motor oil over another.

1. Ambient temperature

Cooler weather conditions require thinner oils (winter grade) to reduce friction and facilitate cold starts. In contrast, higher temperatures require thicker oils (summer grade), which have better film resistance and sealing properties due to their higher viscosity.

The 10W-30 oil considers good for colder temperature areas while the 10W-40 oil performs better in a warmer climate area.

2. Manufacturer specifications

For better lubrication of your engine’s components, it is better to refer to the rating recommended by your manufacturer.

Almost all the engine manufacturers recommend more than one viscosity grade, providing you the option to pick the one that is best suited to your riding condition.

3. Fuel economy

10W-30 oil tends to be more common and widely available, making it less expensive to use. Since the motor uses less energy to pump it, many vehicle owners prefer the 10W-40. However, the use of this type of oil for gasoline mileage is not recommended if it is not what the manufacturer recommends. Consider the possible trade-off between engine longevity and fuel economy when choosing the cheapest option.

4. Engine oil mixture

Despite near to negligible, 10W-30 and 10W-40 motor oils still have performance differences. This is especially true for conventional and synthetic motor oil variants. Synthetic blends provide more effective engine protection and temperature stability than conventional blends. That said, a synthetic 10W-30 can beat a conventional 10W-40 in protecting your ATV’s bearings and piston skirts.

Also, choosing between a standard combination of high mileage 10W30 vs 10W40 depends on the age of your vehicle’s engine. Using more viscous oil for older engines, which is supposed to prevent wear and tear on the oil passages, is a mistake. Modern engines (produced in the last decade) do not benefit from high viscosity oil, as it only adds stress to the oil pump. Choosing a high mileage variant provides older engines with adequate lubrication while resolving seal aging.

5. Viscosity

This aspect is essential when choosing between 10W30 and 10W40 motor oils (and is the focal point of this reading). While both winter oils work the same and reduce drag on cold starts, 10W-40 motor oil is more viscous in warmer climates and has a better temperature spectrum. The 10W-30 synthetic oil range is -25°C / -13°F to 30°C / 86°F (sometimes -30°C / -22°F to 35°C / 95°F) while that of 10W-40 is -30°C / -22°F to 40°C /104°F. Inside your engine, both oil formulas can withstand temperatures up to 100°C / 212°F. But you know what kind of oil will work best.

6. Starburst certification

Look for the oil labels with the correct viscosity and display the API circle with the Starburst symbol. The latest API service standards include SJ, SL, SM, SN, and SP for gasoline engines and CH-4, CI-4, CJ-4, CK-4, and FA-4 for diesel engines. The exploded star symbol indicates that the oil has passed SL service tests and has been verified by the American Petroleum Institute. Some manufacturers may also recommend motor oils under the ACEA and JASO labels.

API-donut-stamps, API-starburst-stamp, API-donut-marks, API-starburst-mark
API Donuts and API Starburst Stamps

7. Your owners’ manual

It is essential to consult your service manual. This reference tells you which lubricant to buy and specifies the level of quality testing the oil should pass. If you have a new vehicle, you should follow the recommendations in the manual.

The car manufacturer always recommended a certain viscosity index for a reason. It is always in your best interest to adhere to this recommendation unless you have a better understanding of the viscosity level that your engine actually requires.


See Also: What Are The Primary Functions Of Motor Oil?

When should you use which?

Ideally, use a 10W30 motor oil if you live in colder climates. Since the ambient temperature will not increase the heat generated by the operation of the engine, you should still be able to maintain the optimum protective characteristics of the engine oil, even when the engine is already at the full accelerator.

However, if you live in warmer areas, you may want to bring 10W40 motor oil. This is especially important on hot summer days when the flaming heat from the sun can amplify the heat generated by your engine.

A 10W30 engine oil will still be able to protect your engine, but it will dilute very quickly and may no longer be able to prevent moving metal parts from getting scratched. So, you will have a much better chance of protecting your engine if you use a 10W40 in hot climates.

10W-40 vs 10W-30 Oil FAQs

  • Will thicker oil stop engine knocking?

Commonly there are different types of engine knocking, that can be cured with different methods. If we talk about piston rod knocking, we can say that it can be stopped by using thicker oil, because it increases the oil pressure.

Although it works temporarily. Whenever the engine oil becomes thin, it will again produce knocking. The final solution is to repair or replace the engine box as soon as possible.

  • Is 10W40 oil thicker than 10W30?

The main difference between 10W30 and 10W40 engine oil is their high-temperature viscosity. Of course, a 10W40 engine oil is thicker than a 10W30 due to its higher viscosity at high temperatures. It has a high ability to maintain its optimum viscous level at the operating condition of the engine.

  • Should I use thicker oil in my old car?

There is a common misconception among people that as the engine getting old, you should replace the current motor oil with a higher viscosity motor oil. This was true for older vehicles, as over time oil flow through friction channels, gets increased in size, and choosing a thicker oil seemed like a smart choice.

In modern vehicles, however, these oil channels remain the same size for the life of the engine. Using a higher viscosity oil may not be beneficial as it can damage internal parts.

See Also: Can I Use 10W-40 Instead Of 5W-30?

10W30 vs 10W40 – Summarizing the whole concept…..!!!!!!!

Both the engine oils can provide proper lubrication, and can efficiently protect your engine against corrosion

There is little difference between these two types of engine oil. What separates them has more to do with temperature fluctuations, engine health, and consumer preferences.

For average weather conditions, any engine oil is an excellent choice. But depending on engine makeup, fuel budget, vehicle usage, and driving style, one can outperform the other.

You can choose any one of them by keeping these precautionary measures in your mind. Again, I’ll recommend you, must consult your owner’s manual to check the better-recommended engine oil according to your riding and weather situation.

Does this article help you better to get the answer to your question? You can ask any other query relevant to the automobiles. We’ll try our best to answer your question as soon as possible.


Your comments are valuable for us.