2008 Subaru Outback Owner's Manual - Page 359

Maintenance and service 11-13 In choosing an oil, you want the proper quality and viscosity, as well as one that will add to fuel economy. The following table lists the recommended viscosities and applicable temperatures. When adding oil, different brands may be used together as long as they are the same API classification and SAE viscosity as those recommended by SUBARU. & Recommended grade and viscosity under severe driving conditions If the vehicle is used in desert areas, in areas with very high temperatures, or used for heavy-duty applications such as towing a trailer, use of oil with the following grade and viscosities is recommended. API classification SM: SAE viscosity No.: 30, 40, 10W-50, 20W-40, 20W-50 ILSAC Certification Mark (Starburst Mark) SAE viscosity number and applicable temperature *: 5W-30 is preferred. API Service label 1) Indicates the oil quality by API designations 2) Indicates the SAE oil viscosity grade 3) Indicates that the oil has fuel saving capabilities Engine oil viscosity (thickness) affects fuel economy. Oils of lower viscosity provide better fuel economy. However, in hot weather, oil of higher viscosity is required to properly lubricate the engine.