What is the difference between 30 and 40 engine oil?
3 Answers
30 engine oil and 40 engine oil differ in the following aspects: 1. Different viscosity: The main difference between 5W30 and 5W40 engine oils lies in their high-temperature viscosity, with 40 oil being more viscous than 30 oil. 2. Different fluidity: 30 oil has better fluidity than 40 oil, which can further reduce fuel consumption and dissipate heat from the engine more quickly. 3. Different maximum applicable temperatures: 40 oil is suitable for higher maximum temperatures compared to 30 oil. 4. Different oil stability: 40 oil exhibits better stability under extremely high temperatures in the engine than 30 oil.
I've been driving for almost ten years and found the biggest difference between 30 and 40 motor oil lies in viscosity. The 30-weight oil flows better, making the throttle feel lighter and more responsive with better fuel efficiency when dealing with frequent traffic lights in city driving. The 40-weight oil has higher viscosity, providing more stable engine sound at highway speeds and offering better protection for engine components during long summer trips. However, it depends on your vehicle model - German cars' manuals often recommend 40-weight oil, while many Japanese new cars perform well with 30-weight. In winter, 30-weight oil warms up faster during cold starts, but for older cars with over 80,000 kilometers, I'd choose 40-weight oil to reduce oil consumption. Always check your maintenance manual before switching - using the wrong oil can actually damage your engine.
As an ordinary working-class car owner, I've specifically compared these two types of engine oil. The 30-weight oil does save fuel – for city commuting, it means one less gas station visit per month. However, during my last road trip under scorching heat, the engine noise became noticeably louder, and the mechanic advised me to switch to 40-weight oil for high-temperature driving conditions. As engine components wear and clearances increase, 40-weight oil forms a thicker protective film. Newer cars run more smoothly with 30-weight oil, but vehicles over six years old should use 40-weight. Now I use 40-weight oil during hot weather and switch back to 30-weight before winter, balancing both economy and engine protection.
