The first number, known as the cold crank viscosity, indicates how easily the oil flows at cold temperatures. The lower the number, the better the oil will flow at cold temperatures, making it easier to start your engine in cold weather.
The second number, known as the high-temperature viscosity, indicates how well the oil resists thinning at high temperatures. The higher the number, the better the oil will protect your engine at high temperatures.
For example, a 5W-30 oil has a cold crank viscosity of 5 and a high-temperature viscosity of 30. This means that the oil will flow easily at cold temperatures but will also provide adequate protection at high temperatures.
It's important to note that the numbers in motor oil are just a general guideline. The best way to determine which oil is right for your engine is to consult your owner's manual.
