What is the difference between 0w40 and 5w40 engine oil?
3 Answers
The difference between 0w40 and 5w40 engine oil lies in their state at low temperatures: 0W40 means the oil remains liquid at minus forty degrees Celsius and will solidify below that temperature; 5w40 means the oil remains liquid at minus thirty-five degrees Celsius and will solidify below that temperature. W40 indicates a viscosity range between 12.5 and 16.3, where 0 represents minus forty degrees Celsius and 5 represents minus thirty-five degrees Celsius. The number before W indicates low-temperature tolerance—the smaller the number, the lower the low-temperature viscosity and the better the low-temperature fluidity. The number after W represents the SAE viscosity range—the larger the number, the thicker the oil, and the higher the summer temperature it can withstand.
That day I helped my elderly neighbor choose engine oil and discovered the key difference between 0W40 and 5W40 lies in low-temperature performance. The number before the W indicates cold-weather viscosity - 0W can withstand -35°C while 5W only goes down to -30°C. During my last business trip to Northeast China at -32°C, cars using 5W40 had obvious starting difficulties with engine knocking sounds, whereas 0W40 worked smoothly. However, both share the same high-temperature protection (the 40 rating), performing equally well during summer highway driving. If you live in southern regions, 5W40 is sufficient and more economical; but for northern areas especially Heilongjiang province, 0W40 is mandatory. One misconception is thinking 0W40's higher price is just marketing hype - actually it uses superior base oil with better low-temperature protection, being particularly friendly to new car engines.
Having worked in the auto parts market for over a decade, I've seen too many cases of wrong engine oil usage. The biggest difference between 0w40 and 5w40 is low-temperature fluidity - 0w provides about 30% faster cold starts in winter compared to 5w. I've tested it in a freezer: at -30°C, 0w40 pours out like salad oil while 5w40 becomes slightly viscous. This difference directly impacts engine lifespan, especially for turbocharged vehicles where cold start wear protection relies on oil flow. Last year when helping a taxi fleet change oil, after switching all Harbin vehicles to 0w40, their engine overhaul rate dropped by 30%. Of course, there's no difference in high-temperature performance during summer - the 40 viscosity rating is completely adequate. If you're south of North China, choosing 5w40 is more cost-effective.
