When you look at a bottle of motor oil, you might see numbers like 15W-50 printed on the label. These numbers might seem confusing at first, but they are actually a simple way to describe how the oil performs at multiple temperatures. This property is called thickness rating, and it’s one of the essential factors in choosing the correct oil for your engine.
Viscosity refers to how heavy or runny a fluid is. Think of corn syrup and mineral oil. Honey is highly resistant to flow—that’s elevated thickness. Water is light and mobile—that’s low viscosity. Engine oil needs to be sufficiently dense to shield engine parts from friction and wear, but thin enough to flow quickly when the engine starts, especially in winter temps.
The numbers on the oil bottle are a dual system. The initial number, followed by the letter w, stands for low-temp. This tells you how well the oil flows at cold conditions. For example, in 5W-30, the 0 means the oil flows well in chilly starts. A lighter grade like 5W 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 lag in cold starts in sub-zero climates.
The second number, after the W, tells you how resistant the oil is at 100°C, which is about 100 degrees Celsius. In 5W-30, the 30 means the oil has a balanced thickness when under load. Greater values like 40 mean the oil stays thicker when the engine is running hot, which can be more effective for older engines that experience thermal stress.
The W in the middle stands for اتوسرویس داوود winter, and it’s there to show that the oil has been tested for performance in wide thermal spectrums. Modern oils are called broad-range lubricants because they can function optimally across a diverse environmental conditions. They contain viscosity modifiers that help them adapt to temperature shifts.
Choosing the ideal thickness matters. If you use oil that’s too thick when cold, your engine may face increased friction on ignition, leading to premature engine damage. If you use oil that’s too light for high temps, it might allow metal contact under performance driving. Always check your vehicle’s service guide for the factory-approved grade. Using the proper grade helps your engine function reliably, extend service life, and can even enhance economy.
In summary, the numbers on your oil bottle are a guide to how the oil responds in different temperatures. The first number before the W tells you about low-temp fluidity, and the hot rating after the w tells you about thermal resistance. Understanding these numbers helps you make a optimal lubricant choice for your car’s reliability.