What is the difference between 15w40 and 10w40?

[StJaxon]

The main difference between 15w40 and 10w40 engine oils lies in their low-temperature fluidity. Engine oil primarily serves the following functions: 1. It effectively protects internal engine components, reducing wear and preventing aging. 2. Inside the engine, it minimizes mechanical friction resistance, ensuring smoother operation. 3. It helps lower the internal temperature of the engine, aids in heat dissipation, prevents rust and aging of internal parts, and extends the engine's service life.

[DiBeau]

The difference between oil viscosity grades like 15w40 and 10w40 mainly lies in low-temperature fluidity. The 'W' stands for winter, where 15 indicates normal flow at around -20°C, suitable for warmer regions, while 10 means better flow at around -30°C, allowing quicker starts in cold weather. Both have the same high-temperature viscosity of 40, offering similar protection under high heat. In southern regions, I often choose 15w40 because winters aren’t too cold, ensuring smooth starts and slightly better fuel efficiency. However, in northern areas or during severe cold, 10w40 is definitely superior, as it helps the engine warm up faster, reducing wear. The car manual usually recommends oil based on regional conditions. Using the wrong type may lead to hard starts or short-trip wear, especially for older cars—don’t risk major damage to save a little. In short, adjust based on climate and vehicle age, and it’s best to have a mechanic evaluate during oil changes.

[DeCali]

As a seasoned driver who has tackled all kinds of road conditions, I find the biggest difference between 10w40 and 15w40 lies in cold-start performance. 10w40 provides smooth ignition during cold snaps without engine shuddering, while 15w40 works great in summer but may cause hesitation in winter. Their protective effects are actually comparable - both maintain stability during high-speed driving in hot conditions. Having tested with my in-car viscometer, I've observed 15w40 maintains viscosity better above 25°C, whereas 10w40 excels in sub-zero temperatures. Choosing the wrong oil increases fuel consumption and noise - I recommend selecting brands based on local weather patterns rather than cutting costs by ignoring seasonal impacts. Regular oil changes also extend engine life.

[AnnieAnn]

Temperature changes cause differences in oil viscosity: 10w40 is thinner at low temperatures, with strong fluidity suitable for cold starts; 15w40 is slightly less thin, performing better in warm weather. Both have the same high-temperature viscosity, offering no difference in driving protection. In extremely cold regions, 10w40 must be used, otherwise, slow starts and increased wear may occur. In warmer areas, 15w40 can be chosen. The wisest choice is to select oil based on the vehicle manual and local weather conditions, as misuse may affect fuel consumption and engine lifespan.