What is the difference between 5W-30 and 5W-40?

[CarolineRose]

The differences between engine oils 5W-30 and 5W-40 can be divided into three main parts, as detailed below: 1. Different kinematic viscosity: (1) Engine oil 5W-30: The kinematic viscosity of 5W-30 at 100°C is 30, which is lower than that of 5W-40. (2) Engine oil 5W-40: The kinematic viscosity of 5W-40 at 100°C is 40, which is higher than that of 5W-30. 2. Different oxidation resistance: (1) Engine oil 5W-30: 5W-30 has poorer oxidation resistance compared to 5W-40, providing weaker protection for the engine during startup. (2) Engine oil 5W-40: 5W-40 has better oxidation resistance compared to 5W-30, providing stronger protection for the engine during startup. 3. Different detergency: (1) Engine oil 5W-30: 5W-30 is more effective than 5W-40 in inhibiting the formation of carbon deposits, varnish, and sludge or in removing these deposits. (2) Engine oil 5W-40: 5W-40 is less effective than 5W-30 in inhibiting the formation of carbon deposits, varnish, and sludge or in removing these deposits.

[HaydenAnn]

5W-30 and 5W-40 are both SAE viscosity grades for motor oil, with key differences in high-temperature performance and application scenarios. 5W-30 has a thinner consistency, offering better low-temperature fluidity—crucial for cold starts in winter or frigid regions, as it allows easier engine cranking and slightly improves fuel efficiency, making daily commutes more economical. 5W-40 is relatively thicker, maintaining more stable oil film at high temperatures to better protect engine components from wear under extreme heat or heavy loads, making it ideal for frequent long-distance travel or aggressive driving. Having driven for a decade, I typically use 5W-30 for city commuting, as it ensures smoother operation; for older vehicles or frequent mountain driving, I opt for 5W-40 to prevent overheating. When changing oil, always check your vehicle manual for the recommended type—using the wrong grade may shorten engine life (e.g., thinner oil provides insufficient high-temperature protection, risking part damage). Regularly monitoring oil level and color is critical to avoid costly repairs.

[Camille]

From a performance perspective, the choice between 5W-30 and 5W-40 affects engine protection at high RPMs. As a modified car enthusiast, I prefer 5W-40 because it maintains a stronger oil film at high temperatures, better handling engine stress to prevent friction and cylinder scoring. In contrast, 5W-30's thinner viscosity suffices for normal driving, but may lead to weaker oil film and increased wear during frequent acceleration or track use. This difference becomes more pronounced as engine temperatures rise, so I insist on 5W-40 for summer or performance vehicles. The number after the viscosity grade determines high-temperature stability - higher values offer better protection. I've seen friends experience increased engine noise from using incorrect oil, so I recommend adjusting based on driving habits. While 5W-40 may consume slightly more oil, protection takes priority. For newer, healthy engines, follow the manufacturer's recommended viscosity.

[DeSienna]

The difference between 5W-30 and 5W-40 is reflected in fuel consumption and environmental protection. Personally, I prioritize fuel efficiency. 5W-30 is thinner, reducing internal engine resistance, which can improve fuel efficiency by a few percentage points, saving money in the long run and reducing carbon emissions. 5W-40 is slightly thicker, increasing engine resistance and resulting in slightly higher fuel consumption, but it offers better protection in high-temperature environments or under heavy loads. The choice involves balancing economy and protection needs. Newer cars often use 5W-30 for energy savings, while older cars or those frequently carrying heavy loads may opt for 5W-40. Climate also affects the choice; thinner oil is preferred in winter to prevent starting difficulties. Regular oil checks and changes ensure optimal performance, while mixing oil types may lead to reduced effectiveness.