See Figures 1 and 2
When adding oil to the crankcase or changing the oil and filter, it is important that oil of an equal quality to original equipment be used in your vehicle. The use of inferior oils may void the warranty, damage the engine, or both.
The Society of Automotive Engineers (SAE) grade number indicates the viscosity of the engine oil, and thus its ability to lubricate at a given temperature. The lower the SAE grade number, the lighter the oil. The lower the viscosity, the easier it is to crank the engine in cold weather but the less the oil will lubricate and protect the engine at high temperature. This number is marked on every oil container.
Oil viscosities should be chosen from those oils recommended for the lowest anticipated temperatures during the oil change interval.
Multi-viscosity oils (10W-30, 20W-50, etc.) offer the important advantage of being adaptable to temperature extremes. They allow easy starting at low temperatures, yet give good protection at high speeds and engine temperatures. This is a decided advantage in changeable climates or in long distance touring.
The American Petroleum Institute (API) designation indicates the classification of engine oil for use under given operating conditions. Only oils designated for use Service SE or SF or greater should be used. Oils of this type perform a variety of functions inside the engine in addition to the basic function as a lubricant. Through a balanced system of metallic detergents and polymeric dispersants, the oil prevents the formation of high and low temperature deposits, and also keeps sludge and dirt particles in suspension. Acids, particularly sulfuric acid, as well as other by-products of combustion, are neutralized. Both the SAE grade number and the API designation can be found on the oil container.
Your Subaru is designed to operate on unleaded fuel. The minimum octane rating of the fuels used must be at least 91 RON. All unleaded fuels sold in the U.S. are required to meet this minimum rating.
Use of a fuel too low in octane (a measurement of anti-knock quality) will result in spark knock. Since many factors affect operating efficiency, such as altitude, terrain, air temperature and humidity, knocking may result even though the recommended fuel is being used. If persistent knocking occurs, it may be necessary to switch to a slightly higher grade of gasoline. Continuous or heavy knocking may result in engine damage.
Your engine's fuel requirement can change with time, mainly due to carbon buildup, which changes the compression ratio. If your engine pings, knocks, or runs on, switch to a higher grade of fuel, if possible, and check the ignition timing. Sometimes changing brands will cure the problem. If it is necessary to retard timing from specifications, don't change it more than a few degrees. Retarded timing will reduce power output and fuel mileage, and will increase engine temperature.