2009 Jeep Grand Cherokee Owner's Manual - Page 358

356 STARTING AND OPERATING for optimum performance. The use of premium gasoline is not recommended, as it will not provide any benefit over regular gasoline in these engines. Light spark knock at low engine speeds is not harmful to your engine. However, continued heavy spark knock at high speeds can cause damage and immediate service is required. Poor quality gasoline can cause problems such as hard starting, stalling and hesitations. If you experience these symptoms, try another brand of gasoline before considering service for the vehicle. Over 40 auto manufacturer's worldwide have issued and endorsed consistent gasoline specifications (the Worldwide Fuel Charter, WWFC) to define fuel properties necessary to deliver enhanced emissions, performance, and durability for your vehicle. The manufacturer recommends the use of gasoline that meets the WWFC specifications, if they are available. Reformulated Gasoline Many areas of the country require the use of cleaner burning gasoline referred to as "Reformulated Gasoline." Reformulated gasoline contains oxygenates, and are specifically blended to reduce vehicle emissions and improve air quality. The manufacturer supports the use of reformulated gasoline. Properly blended reformulated gasoline will provide excellent performance and durability of engine and fuel system components. Gasoline/Oxygenate Blends Some fuel suppliers blend unleaded gasoline with oxygenates such as 10% ethanol, MTBE, and ETBE. Oxygenates are required in some areas of the country during the winter months to reduce carbon monoxide emissions. Fuels blended with these oxygenates may be used in your vehicle.