What is the difference between fully synthetic engine oil 5w30 and 5w40?
2 Answers
Here are the specific differences between fully synthetic engine oil 5w30 and 5w40: 1. High-temperature stability: The number after W indicates the kinematic viscosity of the engine oil at 100°C. A larger number means higher viscosity, which provides better protection and stability at high temperatures, meaning it is less likely to thin out at high temperatures. In other words, 5w40 is more stable at high temperatures than 5w30. 2. Applicability: 5w40 has better viscosity than 5w30, making it more suitable for older cars. 5w30 is more effective in reducing fuel consumption, allowing the engine to dissipate heat faster and better, while also producing less noise, making it suitable for new cars or naturally aspirated engines.
I've been driving for over a decade and have used both these engine oils. The main difference lies in the high-temperature viscosity, indicated by the numbers 30 and 40. 5W30 has lower viscosity at high temperatures, offering better fluidity, making it suitable for new cars or cold winter regions like northern areas. The advantages include reduced engine resistance, better fuel efficiency, and more responsive acceleration. However, during summer long-distance drives or in older vehicles, the oil film might be too thin, increasing wear. 5W40 has higher viscosity, providing stronger protection at high temperatures, especially suitable for hot southern regions or high-mileage older cars where thicker oil is needed to fill enlarged engine clearances. I currently use 40-grade oil myself because my car is eight years old, and it gives me more peace of mind during summer highway driving. For new cars that originally require 30-grade oil, don't change it arbitrarily – always refer to the owner's manual for the most reliable guidance.
