The motor oil you use can significantly impact your engine's efficiency, fuel consumption, and lifespan. That means choosing the right motor oil doesn’t just protect your engine; it protects your wallet. To help you select the proper lubricant for your vehicle’s engine, read on to learn the differences between two of the most popular engine oils: 15w40 and 10w30.

What Are 15w40 and 10w30?

Engine oils are designed to minimize friction between the moving parts of your engine, and how efficiently they do so depends on their viscosity and film strength. Film strength refers to how easily the lubricant breaks down under pressure, while viscosity refers to the thickness of the oil. The lower the viscosity, the easier it flows through the engine.

The names 15w40 and 10w30 refer to the oil grade, and the letter w stands for winter. This tells buyers that the viscosity of 15w40 oil is lower (15) when it’s cold or at starting temperature and higher (40) when the engine is performing. The same applies to 10w30, as the viscosity will be lower when the engine is colder and higher when the engine is hotter. As a general rule, the higher the oil’s viscosity, the higher the oil’s film strength.

What Are the Differences Between Them?

For the most part, both oils are similar. They both provide excellent protection against sludge build-up and oxidation, do well to shield pistons, and can perform under all climate conditions. However, there are a few critical differences.

10w30 is thinner than 15w40, meaning it flows through the engine more easily but doesn’t have as high of a film strength as 15w40. While 15w50 is thicker, it has a higher film strength, offering better part protection. And just by glancing at the numbers, we can tell that 10w30 will perform slightly better in the cold than 15w40, indicating that it is more heat resistant and subsequently less volatile.

Which One Is Best for Your Vehicle?

Now that we know the differences between 15w40 versus 10w30, which one is better than the other? In truth, neither oil is better than the other, and which is best for your vehicle depends on the engine.

10w30 is better suited for passenger vehicles with gasoline engines, especially vehicles that experience low and high temperatures. These vehicles don’t need a high level of film strength as they likely won’t be making back-and-forth cross-country trips that can cause considerable wear and tear on the engine. Conversely, 15w40 is best suited for heavy-duty diesel engines such as high-way fleets, industrial equipment, and tractor-trailers, whose engines will likely see quite a lot of action.

Ultimately, before you opt for any engine oil, you should check your owner’s manual and review what it recommends just to be safe. Fortunately, no matter what oil your vehicle needs, Santie Oil Company can be your one-stop shop for all things oil and lubricant related. From biodegradable multipurpose oil to metalworking fluid synthetic lubricants, we’ve got everything to keep your parts moving and your motor humming.