What is the difference between 10w50 and 10w40?
3 Answers
The following are the specific differences between 10w40 and 10w50: 1. Different viscosity: The number after 'w' represents the high-temperature viscosity of the oil. The larger the number, the higher the viscosity. Therefore, 10w50 oil has higher viscosity. 2. Different usage periods: 10W40 is generally suitable for all seasons, while 10W50 is more suitable for large-displacement vehicles in summer. 3. Different sealing performance: 10W50 has better sealing performance. 4. Different fuel consumption: The higher the viscosity, the higher the fuel consumption. Therefore, a 10W50 engine consumes more fuel, while lower viscosity has the characteristic of saving fuel.
I did quite a bit of research when helping my neighbor choose engine oil. 10W50 and 10W40 look like siblings, with the difference lying in the last two digits. Both have 10W viscosity for cold starts in winter, so their low-temperature fluidity is similar. But during summer road trips or off-roading, the 50 offers significantly better high-temperature protection – it clings tightly to pistons, making it ideal for older high-revving vehicles or those frequently driven on mountain roads, like his 200,000-km Jeep. The trade-off is about half a liter higher fuel consumption compared to 40-weight oil. It's somewhat wasteful for city commuting, but still better than engine seizure. However, never use high-viscosity oil in new cars – excessive oil pump pressure can actually cause damage.
Last time I squatted at the repair shop watching the mechanic change oil and learned: The '10W' in both oils refers to their fluidity at -25°C, ensuring smooth starts in winter. The difference lies in the high-temperature shear value, with 50-grade oil forming a thicker film than 40-grade. Since I love revving high in my manual transmission car during mountain runs, the mechanic filled it with 10W50, saying it can withstand 120°C at 5,000 rpm for solid protection. My eight-year-old hot hatch hasn't shown the oil light since. But using this oil in a new car is like wearing shoes two sizes too big—wastes fuel and hampers performance. For daily grocery-getters, 40-grade is sufficient—don't copy my reckless tinkering.
