When you look at a bottle of motor oil, you might see numbers like 5W-20 printed on the label. These numbers might seem confusing at first, but they are actually a standardized way to describe how the oil performs at multiple temperatures. This property is called fluid resistance, and it’s one of the key factors in choosing the recommended oil for your engine.

Viscosity refers to how viscous or runny a fluid is. Think of honey versus water. Honey is highly resistant to flow—that’s increased resistance. Water is light and mobile—that’s reduced thickness. Engine oil needs to be sufficiently dense to shield engine parts from friction and wear, but light enough for rapid circulation when the engine starts, especially in cold weather.

The numbers on the oil bottle are a two-tiered system. The preceding number, followed by the letter w, stands for freezing conditions. This tells you how well the oil retains mobility at winter climates. For example, in 0W-20, the 10 means the oil remains fluid in cold conditions. A lighter grade like 0W means the oil is more fluid at low temps, which helps the engine crank faster in winter. A larger value like 10W means the oil is less mobile at low temps and may struggle to circulate in sub-zero climates.

The second number, after the W, اتوسرویس داوود tells you how viscous the oil is at 100°C, which is about 212 degrees Fahrenheit. In 10W-40, the 30 means the oil has a medium thickness when under load. Heavier grades like 40 mean the oil stays thicker when the engine is in extreme heat, which can be ideal for performance cars that operate under intense heat.

The W in the middle stands for cold-weather performance, and it’s there to show that the oil has been tested for performance in extreme temperature ranges. Modern oils are called multi-grade oils because they can maintain stability across a wide range of temperatures. They contain viscosity modifiers that help them remain stable as they heat up.

Choosing the right viscosity matters. If you use oil that’s overly viscous in winter, your engine may experience delayed oil flow, leading to excessive friction. If you use oil that’s insufficiently viscous under heat, it might allow metal contact under heavy load. Always check your vehicle’s recommended lubrication chart for the specification code. Using the correct viscosity helps your engine run smoothly, last longer, and can even boost MPG.

In summary, the numbers on your oil bottle are a code to how the oil behaves in varying thermal conditions. The preceding digit before the W tells you about start-up efficiency, and the hot rating after the w tells you about high-temp stability. Understanding these numbers helps you make a smart selection for your car’s reliability.