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

2 Answers

CarolineRose

07/29/25 4:30am

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.

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HaydenAnn

08/12/25 8:12am

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.

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