15W40 oil is thicker than 10W30.
Understanding motor oil viscosity helps determine which oil is thicker. Motor oil viscosity is indicated by numbers like 10W30 or 15W40. The 'W' stands for 'Winter', and the number before it (10 or 15) indicates the oil's viscosity at cold temperatures. A lower number means it's thinner when cold. The number after the 'W' (30 or 40) represents the oil's viscosity at higher operating temperatures (specifically, 100°C). A higher number here indicates a thicker oil at operating temperature.
According to the provided information, "10w30 is thinner than 15w40". This confirms that 15W40 has a higher viscosity compared to 10W30, especially when the engine is at operating temperature. While the 'W' number indicates cold thickness, the second number is the primary indicator of how thick the oil is when the engine is hot and running under normal conditions.
Viscosity Comparison: 10W30 vs. 15W40
Viscosity is a measure of a fluid's resistance to flow. A thicker oil has higher viscosity, meaning it flows more slowly.
- 10W30: Has a cold viscosity rating of 10 and a hot viscosity rating of 30. It is relatively thinner than 15W40 at both cold and hot temperatures. This allows it to flow more easily, particularly in colder climates or during startup.
- 15W40: Has a cold viscosity rating of 15 and a hot viscosity rating of 40. It is thicker than 10W30 at cold temperatures (15 vs 10) and significantly thicker at operating temperatures (40 vs 30). This increased thickness can provide a stronger protective film between engine parts.
Why Viscosity Matters
The correct oil viscosity is crucial for engine performance and longevity.
- Protection: Thicker oils generally provide a stronger protective film between moving parts, which can be beneficial for reducing wear, especially in engines operating under heavy loads or high temperatures. The reference highlights this, stating that while 15w50 is thicker, it has a higher film strength, offering better part protection. Similarly, the thicker 15W40 tends to offer better film strength than 10W30.
- Flow: Thinner oils flow more quickly, which means they can reach critical engine components faster, especially during cold starts. This is where the lower 'W' number of 10W30 might offer an advantage in very cold conditions compared to 15W40, though 15W40 is still formulated to flow adequately in winter temperatures.
- Engine Type: The manufacturer specifies the recommended oil viscosity based on the engine's design tolerances, operating conditions, and expected temperatures. Using the wrong viscosity can lead to excessive wear, reduced fuel efficiency, or even engine damage.
Summary Table
Here's a quick comparison based on typical viscosity properties:
| Feature | 10W30 | 15W40 |
|---|---|---|
| Cold Viscosity | Thinner (Lower) | Thicker (Higher) |
| Hot Viscosity | Thinner (Lower) | Thicker (Higher) |
| Overall Thickness | Thinner | Thicker |
| Flow (Hot) | Flows more easily | Flows less easily |
| Film Strength | Lower | Higher |
Choosing between 10W30 and 15W40 depends on the specific engine requirements, the climate, and the vehicle manufacturer's recommendation. Always consult your vehicle's owner's manual.
