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When you turn the ignition key, you wind up the mechanical heart of your vehicle. Yet, the heart can’t function without lubricating motor oil—the lifeblood of your car. As such, you want to regularly change your vehicle’s oil and ensure that you are using the right kind. However, you may find yourself at a crossroads when your car is low and the correct oil is nowhere in sight. You may find yourself asking, “Can I use 10w40 instead of 5w30?” The answer is not a simple yes or no; it depends on some factors that you are going to learn about in this article.

Table of Contents

Be sure to ask can I use 10w40 instead of 5w30 before you pour oil

What Do The Numbers Mean?

When comparing motor oils, it’s essential to understand what the numbers and letters in the formula mean. The numbers are associated with motor oil grades and tell you valuable information regarding the oil’s viscosity, or thickness. That thickness determines the flow characteristics of the motor oil at different temperatures.

The first number in the formula, such as 10w or 5w indicates the viscosity of the oil in cold conditions. The second number—such as the 40 in 10w40—represents the viscosity at operating temperatures (typically between 75-105ºC. The larger the second number, the more viscous the motor oil will be.

This video discusses viscosity in more detail:

Depending on your vehicle and how it is used the thickness may either benefit or be a detriment to the engine and overall performance. As such, it is highly important that you select the appropriate oil.

What is 10w40 Oil?

10w40 is a versatile grade of motor oil, as it has applications for high-mileage passenger cars (mainly ones from the 1990s or earlier), light trucks, agricultural and industrial equipment, SUVs, and utility vehicles. Looking at the numbers, you can tell that 10w40 is going to be thicker than 0w20 or 5w30. Because 10w40 is more viscous, it will provide enhanced protection to engines in conditions where more heat is generated, such as in severe driving conditions.

What is 5w30 Oil?

5w30 motor oil is a well-rounded grade that’s commonly employed in a wide array of vehicles, making it a popular choice among vehicle owners. If you drive a compact car, crossover, light truck, minivan, or a hybrid vehicle, the manufacturer will likely recommend 5w30. The 5w shows that this oil will be thinner and smoother than 10w in colder weather. The oil’s ability to circulate swiftly upon ignition is vital for preventing excess wear during cold starts.

The “30” shows that, compared to a “40,” that this oil will have a thinner consistency when at standard operating temperature.

How are 5w30 and 10w40 Oil Different?

When you look at 10w40 and 5w30 side-by-side, you can see visible differences in their behaviors when exposed to different temperature ranges. Even if you don’t have both oils available for a visual comparison, the numbers alone can explain quite  a bit about their characteristics.

Here’s a glimpse at how 5w30 and 10w40 compare to each other:

Characteristic5w30 Oil10w40 Oil
Cold Temperature FlowFlows easily at start-up in cold temperaturesThick at start-up, moderate cold-start protection
Operating TemperatureThinner consistency for high-temperature lubricationEnhanced high-temperature protection and friction resistance
SuitabilityIdeal for cold start protection and cold climateIdeal for moderate climates and protection from high heat
AdvantagesReduced friction at high temperatures and superior cold-flowReduced wear on hard-working engines

Let’s take a deeper look at some of these differences:

Cold Temperature Protection

The main difference between 10w40 and 5w30 is how well they protect your vehicle’s engine in the cold. During the winter, your engine is exposed to excessive wear every time you put the key in the ignition. The harder the engine has to work to turn over, the greater the chance of friction and damage. That is why you want a motor oil that is able to flow despite the cold. With a lower first number (5w), 5w30 oil boasts superior flow characteristics during cold starts. In frigid conditions, when the engine is just ignited, 5w30’s lower viscosity allows it to quickly circulate and lubricate critical engine parts.

10w40 can’t compare, as it runs thicker in the cold. That said, while 10w is not going to flow as quickly or efficiently as a 5w, it still provides decent protection in the cold.

Operating Temperature

5w30 functions ideally between -30ºC and 40ºC. For 10w40, it’s between -25ºC and 40ºC. While 5w30 is good for cold weather protection, 10w40 is going to offer more in hotter climates. Although both will protect your engine in the summer, the trade-off with 5w30 excelling in the cold is that its thinner consistency is not as protective as an oil with greater viscosity.

The added viscosity of 10w40 oil means that it provides an additional layer of protection to engine components under high-temperature conditions. The thicker oil film adheres well to engine parts, minimizing wear and enhancing engine longevity.


5W30 vs 5W40 Engine Oil – What’s the Difference?

Can I Use 10w40 Instead of 5w30 in my Vehicle?

The answer is “it depends.” While it is technically possible to use 10w40 oil in place of 5w30, there are important aspects to bear in mind. Because 10w40 is thicker than 5w30, it may not provide the same level of lubrication as the thinner oil would in a colder climate. Or as synthetic oil manufacturer AMSOIL puts it: Some oil is “too thick to flow quickly enough to fill the spaces” between cranks and bearings.

That said, there are some instances where using 10w40 instead of 5w30 could lead to greater wear and friction. Let’s look at some scenarios:

Instances When You Can Use 10w40 Instead of 5w30

1. Moderate Climate: If you live somewhere with moderate temperatures throughout the year, where it is neither extremely hot nor cold, then you may be able to use 10w40 instead of 5w30. A slightly thicker viscosity will not cause significant issues during startup.

2. Heavy Loads and Towing: If you frequently tow heavy loads or engage in activities that put additional stress on the engine, using 10w40 could provide better protection. 10w40 has a thicker viscosity, meaning it can withstand higher temperatures and pressures.

3. High Mileage Engines: High-mileage engines with increased wear may benefit from the slightly thicker protection provided by 10w40. The higher viscosity can help compensate for gaps and wear in the engine components.

Instances Where You Shouldn’t Use 10w40 Instead of 5w30

1. Cold Climate: In colder climates, using 10w40 instead of 5w30 can lead to poor cold-start lubrication. Thicker oil can struggle to flow through the engine’s components during startup, leading to wear.

2. Newer Engines: Many modern engines are designed to operate optimally with specific oil viscosities. Using 10w40 instead of 5w30 in a newer engine could result in reduced fuel efficiency, decreased performance, and potentially void warranties.

3. Short Trips and Stop-and-Go Traffic: If your driving pattern consists mostly of short trips and stop-and-go traffic, using 10w40 might not allow the oil to reach its optimal operating temperature. This can lead to increased engine wear and decreased fuel efficiency.

Can I Mix 10w40 and 5w30?

Mixing motor oils with different viscosities is generally not recommended. Motor oils are carefully formulated to provide specific properties at different temperature ranges, and mixing different viscosities can alter these properties in unpredictable ways.

For instance, mixing 10w40 and 5w30 will create a blend that may not be suitable for your engine. The resulting blend might be too thick for optimal cold-start lubrication and too thin to provide effective high-temperature protection.

Furthermore, mixing different viscosities may impair lubrication. Doing so could compromise the oil’s function, leading to increased friction, wear, and reduced engine efficiency.

Lastly, mixing oils like 10w40 and 5w30 is unpredictable. You never know what you are going to get. The resulting mix may not have the properties you desired. The additives and other components in the oil may also become unstable. This will reduce the overall performance of the oil and negatively impact your vehicle.


Now You Can Choose the Right Motor Oil for Your Vehicle

If you ever wondered, “Can I use 10w40 instead of 5w30?”, you should now have your answer. The numbers on the label of the oil bottle are more than just symbols. They tell you how the oil will behave in your engine at a given temperature. Therefore, if your vehicle is designed to use 5w30 throughout the year, switching to 10w40 may not always be the wisest decision. On the other hand, if you are driving a pickup truck, hauling equipment, and racking up the miles on your engine, using 10w40 could benefit the engine.

FAQs on 10w vs 5w

Can you mix 10w40 and 5w30 oil?

It is not recommended. Mixing oils with different viscosities often yields unpredictable results that may do your engine harm.

Can I substitute 10w40 for 5w30 in my car?

While it is possible to use 10w40 instead of 5w30 in your vehicle, using 10w oil in place of 5w oil could lead to thicker oil at start-up (which can strain the engine). It may cause damage to the engine.

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

Using 5w oil instead of 10w might result in thinner oil at operating temperatures. This could impact engine protection, especially in high-temperature conditions.