When your vehicle is used in high temperature climates, hauling trailers or heavy loads, synthetic ATF is highly recommended. The type and condition of the oil chosen is important. Oil comes in a wide variety of ratings and viscosities, designed for particular applications or vehicle age. In fact, just starting the engine places extreme stress on the engine's oil, especially in winter weather. The way you define your driving habits, environment and the loads you haul or tow, plus the age of your car or truck, will help determine which type and grade of oil you select.
Viscosity is defined as the physical property of any fluid to resist flow when pressure is applied.
The higher the number, the more resistant it is to flow. Obviously, the ability to flow readily is critical to start your vehicle's engine in brutal cold, and calls for a lower viscosity, such as 0W or 5W viscosity grade. For protection against high engine operating temperatures, oil must be able to function and provide the needed lubrication. When the vehicle is operating in summer heat, with temperatures above 80 to 90 degrees day after day, the need is for a high viscosity oil. These oils carry the low temperature flow, and high temperature lubrication properties of the two oils, such as a 0W-30.