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Can You Mix 5W40 And 15W40? The Truth Unveiled.

Published by Dustin Babich on

Yes, it is possible to mix 5w40 and 15w40, but it is not recommended as it could compromise the performance of both oils. Motor oil is an essential component in ensuring your engine runs smoothly and efficiently.

However, using the wrong type of oil or mixing different oils can significantly affect engine performance. One common question that arises among car owners is whether they can mix 5w40 and 15w40 oils. While it’s technically possible to mix these oils, it’s not advisable.

Mixing oils with different viscosities can affect their performance, reducing their overall effectiveness in keeping your engine running smoothly. In this article, we’ll dive deeper into the potential problems that can arise from mixing these two oils and what you should do instead.

Understanding The Differences Between 5W40 And 15W40

Mixing 5w40 and 15w40 oil is a common concern for many car owners. Knowing the differences between these two viscosity grades is important. The viscosity rating indicates the oil’s resistance to flow at different temperatures. 5w40 has a thinner consistency at low temperatures, while 15w40 is thicker.

5w40 oil is best for cold weather conditions, but 15w40 is suitable for warmer temperatures. Additionally, 5w40 oil provides better fuel economy and improved engine performance. On the other hand, 15w40 oil is commonly used in diesel engines and provides better engine protection against wear and tear.

Mixing these oils is not recommended, as the different viscosity ratings can affect the oil’s performance. It’s best to use the recommended viscosity grade for your car’s engine.

The Pros And Cons Of Mixing 5W40 And 15W40

Mixing 5w40 and 15w40 oils can have advantages and disadvantages. The primary advantage is that it can improve your engine’s performance. The mixture of these oils provides better lubrication and viscosity to your engine. This blend may also lead to better fuel efficiency and fewer emissions.

However, there are potential consequences to mixing oils. One of the most significant risks is the impact on your vehicle’s warranty. If your car requires an oil change, using a different oil weight than what is recommended could void your warranty.

You should always stick to the manufacturer’s recommended oil type. Mixing different weights of oil can also create problems and potentially harm your engine. Ensure that you carefully examine and understand the effects of mixing different oils before making any decisions.

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Myth Or Truth: Can You Mix 5W40 And 15W40?

There are common misconceptions regarding the mixing of 5w40 and 15w40 engine oils. Some say it’s fine, while others caution against it. Expert opinions include manufacturers and mechanics who advise against it due to the potential for engine damage. Scientific evidence suggests that even if the mix may not cause immediate harm, it affects the oil’s viscosity and ultimately the engine’s performance.

It is important to stick with the manufacturer’s recommended oil type and grade to ensure the best engine protection. Mixing oils is not worth the risk of damage or engine failure. Always consult with a professional if unsure about which oil to use.

How To Safely Mix 5W40 And 15W40

When it comes to safely mixing 5w40 and 15w40 motor oils, there are certain guidelines to follow. Firstly, it’s vital to mix oils of the same brand and api rating. Additionally, experts agree that mixing should be done in small ratios, such as 1:1, to avoid any engine damage.

Best practices recommend checking oil levels after mixing, and replenishing oil if necessary. Furthermore, manufacturers advise against mixing synthetic and mineral oils. And lastly, if in doubt, it’s always best to consult your owner’s manual or seek advice from a reputable mechanic.

Following these recommendations will ensure the longevity and optimal performance of your engine.

Final Verdict: Should You Mix 5W40 And 15W40?

Mixing 5w40 and 15w40 can compromise the oil’s effectiveness. Factors to consider when mixing include the temperature and engine type. Diesel engines may handle mixing better than gasoline engines. Benefits of mixing may include improved fuel efficiency and engine protection.

Risks include damage to the engine and decreased oil longevity. While it may be possible to mix oils in some instances, it is generally recommended to stick to the manufacturer’s recommendations and avoid mixing. Mixing can have unpredictable effects on your engine’s performance, and may not be worth the potential risks.

Make sure to consult a professional if you are unsure about using two different types of oil in your engine.

Frequently Asked Questions On Can You Mix 5W40 And 15W40

Can I Mix 5W40 And 15W40 Oils?

Yes, you can mix 5w40 and 15w40 oils because they are both multigrade oils. But it’s important to note that the resulting viscosity will be somewhere between the two. Mixing oils can affect the performance, so it’s best to stick to using one type of oil.

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What Happens If I Mix 5W40 And 15W40 Oils?

When you mix 5w40 and 15w40 oils, the resulting viscosity will be somewhere between the two. This can affect the performance of your engine and lead to increased engine wear. It’s best to stick to using one type of oil for optimal engine performance.

Can I Mix Synthetic And Conventional Oils?

Yes, you can mix synthetic and conventional oils, but it’s not recommended. Mixing oils can affect the performance of your engine and lead to increased engine wear. It’s best to stick to using one type of oil for optimal engine performance.

Can I Mix Different Brands Of Oil?

Yes, you can mix different brands of oil, but it’s not recommended. Mixing oils can affect the performance of your engine and lead to increased engine wear. It’s best to stick to using one type of oil for optimal engine performance.

What Is The Recommended Oil For My Engine?

Consult the owner’s manual for your vehicle to find the recommended oil type and viscosity for your engine. Using the recommended oil will help to maintain optimal engine performance and prolong the life of your engine.


Overall, the answer to the question of whether you can mix 5w40 and 15w40 depends on a few factors. While both oils have similar compositions, it’s important to consider the specific circumstances with your vehicle. Mixing the two types of oils could potentially affect the thickness and performance of the engine oil.

It is not recommended to mix oil types unless the manufacturer indicates otherwise. It is always best to refer to the owner’s manual or consult with a mechanic before making any oil changes. Ensuring that you have the proper oil for your vehicle is essential in maintaining its longevity and performance.

By taking the proper precautions and doing your research, you can rest assured that your vehicle will be in good condition and will be able to perform at its best.

Dustin Babich

Dustin Babich

Dustin Babich

As the passionate author behind, Dustin Babich is a knowledgeable expert in all things automotive. With a deep understanding of car tools, equipment, engines, and troubleshooting techniques, Dustin Babich shares invaluable insights, practical tips, and effective solutions to empower readers in overcoming car-related challenges.


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