What is the difference between 5W30 and 10W40 engine oil?
3 Answers
5W30 and 10W40 engine oils mainly differ in: 1. Applicable temperature range: The freezing point temperature corresponding to 5W30 oil is minus thirty degrees Celsius; the freezing point temperature corresponding to 10W40 oil is minus twenty degrees Celsius. 2. Oil viscosity: The high-temperature viscosity of 5W30 oil is 30; the high-temperature viscosity of 10W40 oil is 40. The performance characteristics of engine oil include: 1. Lubricity; 2. Low-temperature operability; 3. Viscosity-temperature characteristics. Engine oil grades are categorized as: 1. AB series: Gasoline and light-duty diesel engine oils; 2. C series: Catalyst-compatible engine oils; 3. E series: Heavy-duty diesel engine oils.
I've been driving in the north for over a decade, and the biggest differences between 5W30 and 10W40 lie in cold-start performance and temperature adaptability. 5W30 has lower viscosity at low temperatures, with the '5' before the W indicating it maintains fluidity even at -30°C, making winter starts exceptionally smooth. 10W40's low-temperature performance is slightly inferior, resulting in some sluggishness during cold morning starts. The situation reverses during summer highway driving—the '40' in 10W40 denotes higher high-temperature viscosity, providing thicker oil film under prolonged high RPMs and better engine protection. My uncle's 200,000-km car stopped burning oil after switching to 10W40, whereas my new car achieves better fuel economy with 5W30. Choosing oil truly depends on local climate and vehicle condition—5W30 is ideal for northern vehicles, while 10W40 is more reliable for year-round high temperatures in the south.
Over the years working in the repair shop, I've found that the most frequently asked question by car owners is about motor oil viscosity grades. The key differences between 5w30 and 10w40 lie in their viscosity index ranges. The smaller pre-W number difference (5 vs 10) indicates better low-temperature fluidity, with approximately 15% less cold-start resistance. The high-temperature viscosity numbers (30 vs 40) reflect oil film thickness at operating temperatures - 40-grade oil forms a film nearly 30% thicker than 30-grade at 100°C. This determines their different applications: new vehicles using 5w30 can achieve 2-3% fuel savings, while older vehicles benefit from 10w40's ability to fill wear gaps. Pay attention to oil certification standards too - European vehicles often require A3/B4 certified 40-viscosity oils, while Japanese models predominantly use 30-viscosity oils.
