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When you look at a bottle of motor oil, you might see numbers like 5W-30 printed on the label. These numbers might seem confusing at first, but they are actually a standardized way to describe how the oil moves at various temperatures. This property is called thickness rating, and it’s one of the critical factors in choosing the recommended oil for your engine.

Viscosity refers to how heavy or runny a fluid is. Think of corn syrup and mineral oil. Honey is thick and flows slowly—that’s increased resistance. Water is thin and flows easily—that’s low viscosity. Engine oil needs to be sufficiently dense to shield engine parts from friction and wear, but fluid enough for instant lubrication when the engine starts, especially in low-temperature environments.

The numbers on the oil bottle are a two-part system. The initial number, followed by the letter w, stands for winter. This tells you how well the oil flows at low temperatures. For example, in 10W-40, the 5 means the oil performs efficiently in cold conditions. A smaller value like 0W means the oil is more fluid at low temps, which helps the engine start more easily in winter. A heavier grade like 15W means the oil is more viscous in chill and may lag in cold starts in freezing temperatures.

The trailing number, after the W, tells you how viscous the oil is at normal engine operating temperature, which is about engine’s optimal thermal range. In 10W-40, the 40 means the oil has a balanced thickness when hot. Heavier grades like 40 mean the oil stays thicker when the engine is in extreme heat, which can be better for performance cars that generate more friction.

The W in the middle stands for low-temp rating, and it’s there to show that the oil has been rated for performance in both cold and hot conditions. Modern oils are called all-season oils because they can maintain stability across a extensive climate zones. They contain thermal stabilizers that help them adapt to temperature shifts.

Choosing the correct grade matters. If you use oil that’s overly viscous in winter, اتوسرویس داوود your engine may not get enough lubrication, leading to extra wear. If you use oil that’s too light for high temps, it might fail to maintain film strength under heavy load. Always check your vehicle’s service guide for the specification code. Using the correct viscosity helps your engine run smoothly, last longer, and can even improve fuel efficiency.

In summary, the numbers on your oil bottle are a guide to how the oil performs in varying thermal conditions. The W-prefix value before the W tells you about start-up efficiency, and the following digit after the W tells you about operating viscosity. Understanding these numbers helps you make a smart selection for your car’s reliability.