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Although it is recommended by vehicle manufacturers to use the same oil every time you change your motor oil, there are some instances where you might need to use something different. Maybe you are even tempted to mix two oils together. If you’ve ever found yourself wondering, “Can you mix 5w30 with 10w30?” you’re not alone. The world of engine oils can be a bit confusing, especially when it comes to mixing different grades. Let’s look at the details to see if blending 5w30 and 10w30 is advisable, as well as how to mix oils of similar viscosity together.

Table of Contents

black and white plastic bottle of 5w30 motor oil

Can You Mix Engine Oils of Similar Viscosity?

The viscosity of an engine oil, as indicated by the numbers before and after the “w” (winter), plays a crucial role in determining how well the oil flows and lubricates your engine. Oils with similar viscosities, such as 5w30 and 10w30, are designed to offer optimal performance in various temperature conditions. When it comes to mixing engine oils with the same viscosity, you’re on safer ground. Oils of the same viscosity share similar flow characteristics, ensuring that they can blend seamlessly within your engine’s components. This compatibility reduces the likelihood of encountering compatibility issues or adverse reactions.

Can You Mix 5w30 and 10w30?

Yes, you can mix 5w30 and 10w30 oils. You can do so for the same reason you can use 10w30 instead of 5w30 in most vehicles. These oils share a close viscosity profile, making them compatible for blending. The concern often centers around potential engine damage, but when it comes to oils of similar viscosities, there is no need for worry. Mixing 5w30 and 10w30 will not harm your engine; in fact, it’s a safe practice.

Potential Impact of Mixing Engine Oils

While you can generally mix engine oils of a similar viscosity, such as 5w30 and 10w30, there are some things you need to keep in mind. You ideally want to stick to the same brand to ensure the proprietary additive blends remain the same. Sometimes mixing oils of different brands—even when they are the same viscosity—can introduce additives that do not play well together. This could potentially cause performance issues. Furthermore, always mix synthetics with synthetics, never a synthetic and conventional oil, for the same reason: additives.

Secondly, while you can mix 5w30 and 10w30 with minimal risk, avoid mixing oils with different weights. Engine oils with different weights may not provide the desired level of lubrication under certain conditions.

This video provides some further information on mixing oils:

Differences Between 5w30 vs 10w30

There are not many differences between these two motor oils, except for the “5w” and “10w.” These numbers represent the viscosity at cold temperatures, particularly during winter months. In this context, lower numbers signify thinner oils that can flow more easily during cold starts, safeguarding critical engine components.

Both 5w30 and 10w30 oils share a comparable viscosity range when your engine is running at its normal operating temperature. This characteristic ensures that, once the engine warms up, both oil grades provide effective lubrication and protection to the various moving parts within the engine.

However, their properties vary when its cold. The “5w30” designation indicates that the oil maintains its fluidity at cold temperatures down to approximately -35°C (-31°F). Similarly, 10w30 oil is slightly thicker when cold. It remains fluid even at temperatures as low as approximately -30°C (-22°F).

How Should You Mix 5w30 and 10w30 Together?

Mixing 5w30 and 10w30 oils is a straightforward process that can be done directly in your vehicle’s engine. You can do this when changing your oil or when topping off. Just remember to let the engine cool slightly after running it, as some of the parts and oil may be hot.

Here are the steps to ensure effective blending:

  1. Prepare the Oils: Gather both 5w30 and 10w30 oils. Ensure that you have the correct quantities of each oil based on your engine’s capacity.
  2. Choose a Funnel: Using a clean funnel designed for pouring oil into the engine is crucial to prevent spills and contamination.
  3. Start with 5w30: Place the funnel in the oil filler hole and pour the 5w30 oil directly into the engine. This lighter-weight oil will serve as the base for the mixture.
  4. Add 10w30: After pouring the 5w30, directly pour the 10w30 oil into the engine through the funnel. Always add the denser oil after the lighter oil. This will assist with the blending process.
  5. Mix Naturally: Turn on your car for a few minutes. As the engine runs, the movement of the oils and the heat from the engine will naturally blend the two oils together.
  6. Check Oil Level: Once again, let the engine cool for a few minutes to let the oil settle. After adding the oils, use a dipstick to check the oil level and ensure it is within the recommended range.

What Happens When You Mix 5w30 with 10w30 Oil?

Although you are already aware of some of the potential impacts of mixing motor oil together, let’s consider what happens when blending 5w30 and 10w30 specifically. While no significant damage will be done, it’s important to understand how the oil may change once mixed.

From a technical standpoint, the resulting blend tends to lean more towards the characteristics of 10w30 oil and may not fully exhibit the distinctive benefits of 5w30 oil. The difference lies in their viscosities at different temperatures. Though both maintain the same weight and flow at operating temperature, they function differently in the cold.

Given that 10w30 has a slightly higher density than 5w30, the flow may concentrate towards the top of the engine. This is a characteristic of higher viscosity oils in colder temperatures.

As such, you won’t get the benefit of 5w30 in cold weather. This may lead to compromised performance in colder climates. You may also have a shorter oil change interval. That said, if you plan on going on a road trip or hauling something substantial, 10w30 characteristics may be beneficial. The heavier 10w30 oil is well-suited for handling heavier loads in cold conditions, while the lighter 5w30 oil excels in providing superior lubrication. By recognizing the strengths of each oil type and selecting them based on your specific needs, you can make the most of their individual advantages.

When Should You Mix 5w30 and 10w30 Together?

There are plenty of scenarios that call for mixing oil. Here are some instances when you can mix these two oils and receive some benefits:

  • Fluctuating Temperatures: If you live in an area with significant temperature variations throughout the year, mixing these oils can provide consistent engine lubrication. The lighter 5w30 oil will aid in cold start-ups, while the slightly thicker 10w30 oil will offer protection during warmer conditions.
  • Moderate Climate: In regions with moderate climates where extreme temperatures are rare, using either 5w30 or 10w30 oil might suffice without the need for mixing.
  • Heavy Load and High Temperatures: If you regularly operate your vehicle under heavy load or in hot conditions, the additional viscosity of 10w30 oil could offer better protection for your engine.
  • Topping Off: You are running low on oil and need to top it off before you can get to the mechanic. Even if you can’t get a hold of the recommended oil, mixing 5w30 and 10w30 will not harm you vehicle. This ensures you get to where you are going without running low on motor oil.

Final Thoughts on Mixing 5w30 with 10w30

Can you mix 5w30 and 10w30 oil without causing damage to your vehicle? The answer is yes. That said, it is important to consider the trade-off. The resulting mixture will be a blend, meaning that it may not protect your engine as well as 5w30 or 10w30 would. Therefore, while mixing 5w30 and 10w30 is acceptable and sometimes advantageous, it is also prudent to maintain your engine’s functionality and performance in the long term with routine oil changes.


What happens if you put 10w30 in a 5w30?

Putting 10w30 in a vehicle designed for 5w30 is generally safe. The difference in viscosity between the two oils is minimal, and modern engines are designed to tolerate slight variations.

Are 5w30 and 10w30 interchangeable?

Yes, 5w30 and 10w30 oils are interchangeable in most cases. Their similarities in viscosity at operating temperatures make them compatible for use in similar conditions.

What happens if you put 10w oil in 5w?

Putting 10W oil in a vehicle designed for 5W oil might slightly affect cold-start performance. The 10W oil may be slightly thicker in cold temperatures, leading to slower initial flow. However, the difference is usually negligible and won’t cause significant harm to your engine.

What happens if you put 5w oil in 10w?

Using 5W oil in a vehicle designed for 10W oil can lead to better cold-start performance. The 5W oil is thinner at lower temperatures, allowing it to flow more easily during start-up. Yet, for heavy machinery or larger trucks, 5w may be too thin to provide adequate lubrication.

Does mixing different types of engine oil damage your motor?

Mixing oils of the same viscosity and API rating generally doesn’t damage your engine. However, mixing oils with different viscosities or brands can have unpredictable effects.