What is the difference between 5W-30 and 5W-40 engine oil?
3 Answers
The differences between 5W-30 and 5W-40 engine oil: 1. Different viscosity: The viscosity grade of 5W-30 engine oil at 100°C is 11cst; the viscosity grade of 5W-40 engine oil at 100°C is 14.5cst. 2. Different stability: Under high-temperature conditions, 5W-40 is more stable than 5W-30. 3. Different sealing properties: 5W-30 has lower sealing performance; 5W-40 has higher sealing performance. Engine oil, motor oil, or engine lubricant is a substance enhanced with additives in base oil, mainly containing anti-wear additives, detergents, dispersants, and multi-grade viscosity index improvers. Engine oil is used for lubricating internal combustion engines. The main functions of engine oil are to reduce friction and wear of moving parts and to remove sludge (one of the functions of dispersants) and varnish (function of detergents) from the engine.
I've observed many engine issues over time, and the biggest difference between 5W-30 and 5W-40 lies in their high-temperature viscosity. 5W-30 flows faster during hot weather driving, helping to reduce fuel consumption, especially saving energy in new cars. 5W-40 is slightly thicker, providing better protection for engine components during high-speed summer driving and reducing wear. In terms of cold starts, both use 5W, so there's little difference in winter startup. Older cars or turbocharged engines are recommended to use 5W-40, otherwise, the oil film may be too thin and cause leaks. New car manuals typically recommend 5W-30—don't casually switch to thicker oil as it may waste fuel money or even damage the engine. When engine temperatures are high, closely monitor oil pressure, and regular checks are crucial.
As someone who has driven for over a decade, I've tried different motor oils. Both 5W-30 and 5W-40 perform similarly during cold starts, flowing easily. However, during long-distance drives or in hot weather, 5W-40 has stronger viscosity, providing more stable engine operation—my old SUV runs quieter with it. 5W-30 is thinner, offering better fuel efficiency for city driving and saving some money on gas. Never mix them or switch randomly based on sales pitches—always check your car's manual for safety. Good car maintenance affects longevity, so I always remind friends to check the dipstick monthly.
