What Do Engine Oil Specifications Mean?
3 Answers
The specifications such as "15W-40" and "5W-40" can be explained as follows: The "W" stands for Winter. The smaller the number before the "W," the better the oil's low-temperature fluidity, indicating it can be used in lower environmental temperatures and provides better engine protection during cold starts. For example, 5W can withstand external temperatures as low as -30°C, while 20W can only withstand -15°C. Here is some relevant information: Viscosity: The number after the "W" represents the oil's kinematic viscosity at 100°C. A higher number indicates higher viscosity. For instance, 40 means the kinematic viscosity standard at 100°C is between 12.5mm²/s and 16.3mm²/s. It absolutely does not mean the oil can be used below 40°C, as some misconceptions suggest. Oil Classification: Engine oils can be categorized into different specifications based on viscosity and quality. If a car is used in cold regions like Northeast China and has undergone routine maintenance before winter, the oil used is likely a low-temperature-resistant type with better performance in cold-start conditions. However, as temperatures rise, switching to an appropriate oil grade ensures the engine operates in its optimal state.
I've been driving for over a decade and have deep feelings about the meaning of motor oil grades. For example, in 5W-30, the 5W indicates low viscosity during cold starts - the smaller the number, the easier it flows at low temperatures, with W standing for winter. The 30 represents viscosity at high temperatures - higher numbers mean thicker oil with better protection. API ratings like SP indicate oil quality, with more additives reducing engine wear. Choosing the wrong grade, like using 10W-40 in winter, makes the oil too thick, causing difficult starts and higher fuel consumption. I once did this and ended up with louder engine noise. Regular oil checks and following the manual's recommendations keep your car running smoothly and extend its life. You can slightly adjust grades between seasons but avoid major changes. Synthetic oils flow better but cost more, suiting new cars; mineral oils are cheaper and better for older vehicles. Remembering the correct grade saves fuel and money while reducing maintenance hassles.
From the perspective of engine oil specifications, they indicate the performance indicators of the oil. For example, in 5W-30, the number before the W in the SAE standard, such as 5, represents the low-temperature viscosity—the smaller the value, the faster the engine starts in winter. The 30 denotes the high-temperature viscosity value; a higher value means stronger protection at high temperatures. API ratings like CK-4 indicate higher oil quality with more additives. Fully synthetic oils have stable molecules, excellent oxidation resistance, but are more expensive; semi-synthetic or mineral oils are more economical but prone to degradation. Using the wrong viscosity can increase friction, fuel consumption, and damage the engine. I often help people inspect cars, and it's crucial to match the oil specification to the vehicle manual—don't switch randomly. Modern oils also focus on low ash content to reduce emissions. In regions with significant temperature variations, choosing the right specification ensures proper lubrication. Regular oil changes maintain cleanliness and prevent engine issues. Good oil can make driving smoother and save fuel.
