It depends. Some vehicle manufacturers provide a range of recommended motor oil viscosity grades based on the outside temperature in which the car is driven. Other manufacturers recommend the use of only one motor oil viscosity grade. For best engine performance, always follow the manufacturer's recommendations found in your vehicle’s owner’s manual.

The "w" in motor oil stands for winter. The first number in the oil classification refers to a cold weather viscosity. The lower this number is, the less viscous your oil will be at low temperatures. For example, a 5W- motor oil will flow better at lower temperatures than a 15W- motor oil. The higher number, following the “w” refers to hot weather viscosity, or how fluid your oil is at hot temperatures. The higher the number, the thicker the oil at a specified temperature.

The starburst symbol means that the oil meets the requirements of the International Lubricants Specification Advisory Committee (ILSAC) in addition to the requirements of API, as stated in the API starburst symbol on the back of the bottle. Only certain viscosity grades are eligible for the starburst symbol.

Some motor oil brands claim 20,000-mile oil change intervals. But it comes down to individual driving habits, conditions, and ultimately what’s recommended in your vehicle owner manual. Valvoline recommends referring to your owner’s manual for oil change intervals.