10W30 vs 15W40: Differences, Performance, Compatibility, and More!

Last Updated on May 10, 2024 by Azim Uddin

With the rise of modern engines with smaller oil passages, thinner engine oils are now preferred by drivers. This is why more people are choosing 10W30 motor oils over 15W40 oils. In our 10W30 vs 15W40 guide, we’ll discover which one is actually better for your vehicle.

As 10W30 grade oils are thinner, they flow faster and offer more fuel economy. They are great for cold starts and proper lubrication of medium-sized vehicles. 15W40 oils are thick, so they provide better protection even at higher temperatures, especially for heavier vehicles.

Let’s dive in and find out the key differences and similarities between 15W40 and 10W30 engine oils.

15W40 Vs 10W30: A Quick Overview

Before we jump into the details, here’s a quick look at the comparable features of 10W30 and 15W40 engine oils:

Comparable Features	10W30	15W40	Winner
Viscosity and Thickness	Low viscosity; thinner	High viscosity; thicker	Depends on the engine type
Cold Temperature Performance	More effective due to its low viscosity	Less effective as it’s thicker	10W30
High-Temperature Performance	Breaks down faster than 15W40	More effective in high temperatures	15W40
Film Strength and Oxidation	Weaker film strength and more prone to oxidation	Stronger film strength and more resistant to oxidation	15W40
Compatibility with Vehicle Types	More versatile; suitable for most passenger cars and SUVs	Less versatile; best for heavy-duty vehicles	10W30
Fuel Efficiency	More fuel economical	Less fuel efficient	10W30
Price	Costs less than higher viscosity oils	A bit pricey for the added additives	10W30

Basic Understanding of 15W40 and 10W30

Let’s start with the key difference between the two oil grades. According to the SAE oil codes, the ‘W’ in a grade refers to ‘Winter’.

• First Number: In the codes 10W30 and 15W40, the first numbers refer to the viscosity or thickness of the oil at cold temperatures (tested at 0°F). As the 10W30 has a lower first number than the 15W40, it’s less thicker in extreme cold.

Meaning, the 10W30 flows more easily through the engine components and lubricates them faster.

• Second Number: Similarly, the second number stands for oil viscosity or thickness at high temperatures (tested at 210°F). The 10W30 has a lower viscosity rating, so it’s thinner than the 15W40 when the conditions are hot inside the engine.

A thin oil like the 10W30 is more likely to break down and not offer sufficient lubricant in high heat. With its high viscosity rating, 15W40 withstands higher temperatures and offers more protection for the engine parts.

15W40 Vs 10W30: Side-By-Side Comparison

Now that you understand the significance of the oil grades, let’s find out how they differ. Here’s a detailed comparison of 10W30 and 15W40 SAE oil grades.

Cold Temperature Performance

With a lower viscosity, the 10W30 flows more easily at cold temperatures. It allows the engine to start faster and reduces wear and tear on the engine components.

On the other hand, 15W40 oils show more resistance to flow in extreme cold. Therefore, they can potentially cause more wear on engine components.

High-Temperature Performance

At high temperatures, thinner engine oils tend to break down faster and fail to offer sufficient lubrication. 15W40 oil has a higher viscosity in extreme hot temperatures than 10W30 oil. Therefore, it lubricates the engine parts better and offers greater protection under high shear stress.

While not as thick as 15W40 oils, 10W30 oils are usually sufficient for modern engines operating at standard temperatures.

Film Strength and Oxidation

The film strength of engine oils indicates how well they resist breakdown under pressure and shear stress. A strong oil film protects the engine components from wear and tear.

While 15W40 oils have a stronger film strength and provide better protection, 10W30 oils also offer sufficient protection for the engine. However, thicker lubricants like the 15W40 motor oils are more oxidation-resistant.

Hence, they don’t form sludge and deposits, which easily clog the engine and reduce the engine’s lifespan. So, when it comes to offering protection and extending the engine’s life, 15W40 oils are a better choice.

Fuel Efficiency

According to research, when you reduce the viscosity of gear oil by only one SAE grade, the fuel efficiency increases from 0.4% to 2.5% at high and 0.2% to 1.5% at cold temperatures.

The same applies to engine oils, and going for an engine oil with a lower viscosity grade will be more fuel-economic and environment-friendly. This means 10W30 oils offer better fuel efficiency as they flow more smoothly and reduce internal friction.

Compatibility With Vehicle Types

Generally speaking, 10W30 motor oils are more versatile as they are compatible with a wide range of vehicles. Modern vehicle engines come with small oil passages, so thinner oils easily reach the moving parts of such engines.

Hence, 10W30 oil is more suitable for modern passenger cars and light- to medium-sized trucks.

On the other hand, 15W40 oils are preferred for older and heavy-duty vehicles, like trucks, agricultural equipment, and some diesel engines. If you own a high-mileage model or an older engine, go with 15W40-graded oils.

Price Range

10W30 oils are typically cheaper than 15W40 oils as they contain a lesser amount of additives. 10W30 oils are thinner and less expensive to produce.

However, the price can vary depending on the oil brand, type of oil (synthetic, conventional, or blended), and oil quality. On average, each quart of 10W30 oils costs $4.49. For every quart of 15W40 oil, you need to spend $4.75.

Pros and Cons of 10W30 SAE Grade Oils

Now, let’s take a look at the advantages and disadvantages of using 10W30 SAE-grade oils. It will help you understand whether this oil is the right pick for your vehicle.

Pros

• Highly Versatile; suitable for most modern vehicles, including passenger cars and SUVs
• Flows better and faster than higher-graded oils at extremely low temperatures
• Offers great lubrication for the engine parts and withstands wear and tear for a long time
• More cost-effective compared to some specialized synthetic oils or lower-viscosity oils
• Designed for everyday driving and mixed driving conditions, including city and highway driving

Cons

• Not as effective as high-viscosity oils at high temperatures
• More prone to oxidative damage, which decreases the engine’s lifespan

Pros and Cons of 15W40 SAE Grade Oils

What are the benefits of using higher viscosity 15W40 oils? And when not to choose them? Let’s weigh their good sides and drawbacks to find out!

Pros

• Its high viscosity offers excellent protection for the engine components against friction
• Great for high-performance engines and heavy-duty vehicles
• Doesn’t easily break down at high temperatures, avoiding potential wear
• It is more resistant to oxidation, so it reduces the amount of sludge and deposits
• Handles high-pressure and heavy loads better than thin oils

Cons

• It is less suitable for modern engines with small oil passages
• Increased fuel consumption when compared to thinner oils

Final Verdict

Still stuck in the 10W30 vs 15W40 debate? Let’s choose the better one, then. After considering all the features and drawbacks of both SAE grades, we’ve chosen the 10W30 as the better grade. It’s more versatile, handles a wide range of temperatures, and offers great protection.

Moreover, 10W30 oils are cheaper and more fuel-efficient. However, if you own a high-performance vehicle or carry heavy loads regularly, 15W40 is definitely a better option. This oil is great for high temperatures and maximum protection against wear.