What does 5w40 engine oil mean?
3 Answers
5w40 engine oil means: 1. 'w' stands for winter, indicating it's for winter use; 2. The number 5 before 'w' represents the viscosity at low temperatures - the smaller the number, the better the fluidity in cold conditions and stronger cold resistance; 3. 40 refers to the viscosity at 100°C - the higher the number, the greater the viscosity and better high-temperature resistance. Engine oil, also known as motor lubricant, functions to: 1. Lubricate and reduce friction; 2. Assist in cooling; 3. Seal and prevent leaks; 4. Prevent rust and corrosion; 5. Absorb shock and cushion impacts. The composition of engine oil includes: 1. Base oil: The main component that determines the fundamental properties of the lubricant; 2. Additives: These compensate for and improve any deficiencies in the base oil's performance.
My Volkswagen has been running for seven years, always using 5w40 oil, simply put, it's an oil grade with a wide temperature adaptation range. The 5 before the W indicates low-temperature performance—the smaller the number, the better the low-temperature fluidity, allowing smooth starts even at -30 degrees Celsius in winter. The 40 refers to high-temperature viscosity, meaning it can still maintain a protective oil film when the engine operates at over 100 degrees. This type of oil is suitable for all seasons, especially for German cars and southern regions. During the last maintenance, the mechanic mentioned that it balances cold-start protection and high-speed wear resistance, making it ideal for someone like me who frequently drives on highways. However, if the new car manual specifies 0w20, it's best to follow the manufacturer's requirements—choosing the wrong viscosity can affect fuel consumption.
I've been dismantling and repairing engines for over 20 years, and I see the 5W40 grade every day. The 5W indicates it passes the -30°C low-temperature test, allowing quick pumping to all components during cold starts. The 40 represents a high-temperature kinematic viscosity between 12.5-16.3mm²/s, meaning it can withstand even when the turbocharger glows red. Mineral, semi-synthetic, and full synthetic oils can all achieve this grade, but full synthetics offer better high-temperature stability. During repairs, I've found this viscosity particularly suitable for older vehicles - even with worn piston ring gaps, they don't burn oil. Of course, modern vehicles tend to prefer lower viscosity oils, but this ultimately depends on the specific vehicle condition.
