Can You Mix 5W-30 and 5W-40 Engine Oil?

Internal combustion engines require an input of engine oil now and then. Engine oil lubricates engines and protects them against seizing up and rust. However, some people recommend 5W-40 oil while others advocate for 5W-30 oil, but what happens when you mix the two?

You can mix 5W-30 and 5W-40 oil. You can use various mixtures of the two oils as they are miscible, which means that they easily mix into one solution. You can mix several types of engine oil as long as the same brand produces them. But, the base oil needs to be the same.

You’ll want to keep reading to learn more about engine oil, specifically the differences between different types of motor oil and how to use them effectively and safely. By the end of this article, you will have gained insight into how motor oils interact with one another and how you can best maintain your car engine.

Is It Recommended to Mix 5W-30 With 5W-40?

We’ve already established that you can mix 5W-30 with 5W-40 without causing catastrophic damages to your engine. However, we still haven’t explored whether you should mix these oils in your engine. Is it a wise decision to mix 5W-30 and 5W-40 in an operational combustion engine?

It is not recommended that you mix 5W-30 with 5W-40 in your engine. However, if you are low on engine oil, using 5W-30 instead of 5W-40 is better than continuing without oil. As long as the engine oils you mix are manufactured by the same brand, they should be fine to mix.

The issue with mixing different forms of engine oil is the unknown properties of the mix of oils.

As a result, this may lead to issues in your engine if you continue to mix oils or use inappropriate engine oil for an extended period.

Engine oils are precisely manufactured to be of a specific weight and viscosity. Viscosity is how thick a liquid is and how it resists deformation. As a result, mixing the oils may sauce the properties of the oil, which could have adverse side effects that are hard to predict.

Therefore you should use the correct engine oil for your car’s engine to prevent any potential issues.

What’s the Difference Between 5W-30 and 5W-40?

There are various types of engine oils available for you to buy. When you are presented with so many options, it can be difficult to decide, especially when you don’t really know the difference between engine oils. So what differences, if any, are there between 5w30 and 5w40?

The difference between 5W-30 and 5W-40 is that they perform differently at higher temperatures. 5W-40 outperforms 5W-30 at high heat, which makes this oil ideal for use in warmer climates.

5w40 operates better at high temperatures due to its viscosity properties when heated to a specific high temperature.

To better understand what 5W-30 and 5W-40 are, you can break down their names to learn about their properties. They both have “w” in the middle of their names, and they both start with the number 5.

We’ll get to more of that later, but for now, let’s focus on the last number in their names.

The last numbers in 5W-30 and 5W-40 are 30 and 40, which represent the viscosity of the oils when heated to a high temperature. Ensuring that the engine oil you use is the correct viscosity is essential.

If your engine oil is too viscous, it will harm performance as it will slowly meander through the engine. At the same time, engine oil with low viscosity will facilitate performance while failing to protect moving parts in the engine.

If you are considering buying engine oil for your car any time soon, check out these great options available to buy on

Is 5W-30 or 5W-40 Better for Winter?

Now that you know what the differences between 5W-30 and 5W-40 engine oil are, it’s time to figure out when you should use each type. For instance, should you be using 5W-30 during the cold winter months as we already know that 5W-40 is better for the summer in hot climates?

5W-30 and 5W-40 are both good in the winter, and as a result, neither version of engine oil is better for winter. The “5W” at the start of their names means that they have the same viscosity at low temperatures and are winter-suited engine oils suitable for cold climates.

Both engine oils have a cold-weather viscosity of 5, which is relatively low.

The w means winter, and the number before it refers to how well it will flow in the wintertime. A low number means that it flows better. Engine oil that starts with a 10 or 15 would not perform well at lower temperatures, unlike when it starts at 5.

The names given to engine oils were developed by the Society of Automotive Engineers (SAE).

SAE names show the properties of the oil, with the first number indicating performance at low temperatures and the numbers at the end indicating performance at high temperatures. As a result, the climate can influence which engine oil is best for your car.

Will the Wrong Engine Oil Damage Your Car?

When damages occur to a vehicle’s engine, it likely means an expensive trip to the shop is soon to follow. Taking care of your car correctly is essential in protecting yourself financially and avoiding inconvenience. So can using the wrong engine oil result in a trip to the mechanic?

Using the wrong engine oil on your car won’t cause extensive damage on a one-off. However, if you use low viscosity engine oil in a hot climate, the engine will not receive proper lubrication, which can cause severe damages to moving components within the engine.

In contrast, using high viscosity engine oil in cold climates may cause blockages in the engine. This likely won’t cause any severe harm to the engine, however, or the vehicle will be slow to start if it does at all.

Ensuring that your car engine is continuously topped up with engine oil is vital in protecting the engine and increasing the longevity of your car’s life.

Adding motor oil is one of the most critical maintenance on your car engine.

Can You Mix Synthetic Oil and Conventional Oil?

When choosing which engine oil is best for your car, you will likely come across synthetic and conventional options. Synthetic oils typically outperform conventional engine oils in protection and lubrication. So is it safe to mix synthetic and conventional oils in your engine?

You can mix synthetic oil and conventional oil in an engine without causing damage to the vehicle. However, the performance of the mixture of oils will be inferior to the synthetic motor oil performance by itself.

Mixing 5W-30 and 5W-40: Final Thoughts

You can mix 5W-30 engine oil with 5W-40 engine oil inside the engine of your car.

However, you should avoid doing so to protect your engine against potential issues that could arise. Ensuring that you use the proper engine oil is essential in protecting your car while allowing for the best performance. 

The main differences between 5W-30 engine oil and 5W-40 engine oil are seen at higher temperatures. At low temperatures, both of these oils perform and behave almost identically. As a result, both variations are ideal for cold climates.



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