You can improve your gas mileage by 1-2 percent by using the manufacturer*s recommended grade of motor oil. For example, using 10W-30 motor oil in an engine designed to use 5W-30 can lower your gas mileage by 1-2 percent. Using 5W-30 in an engine designed for 5W-20 can lower your gas mileage by 1-1.5 percent. Also, look for motor oil that says "Energy Conserving" on the API performance symbol to be sure it contains friction-reducing additives.The viscosity grade (for example, 5W-30) tells you the oil*s thickness, or viscosity. A thin oil has a lower number and flows more easily, while thick oils have a higher number and are more resistant to flow. Water has a very low viscosity * it is thin and flows easily. Honey has a very high viscosity * it is thick and gooey. For a low viscosity oil such as 0w20 it produces less "drag" on the motor, which in turn can use less fuel because less work is required to be efficient.
Vehicles are developed and tested to determine what fluids are well suited for performance and
durability. If Toyota recommends 0w20 I would use that, they know best. Also there could be a warranty issue if you don*t use what they recommend.
〉 Answered on Oct 17th, 2008 by Donna Burmeister, Service Manager at Classic Nissan
The numbers used to identify different oils refers to the oils viscosity - basically how thick or thin the oil is. The difference between zero and five is very minimal. I wouldn*t see a problem with using 5. However, I always suggest that the maker of the vehicle knows best. Also, if you ever have any engine problems and it is known that you*re not using the recommended oil, it could void the warranty.
〉 Answered on Oct 17th, 2008 by Suzanne Grego, Technician at City of Philadelphia Fleet Management