2005 Mercedes CLK-Class Owner's Manual - Page 308

Operation At the gas station Warning! G i Only use premium unleaded gasoline with a minimum Posted Octane Rating of 91 (average of 96 RON/86 MON). Information on gasoline quality can normally be found on the fuel pump. For more information on gasoline, see "Premium unleaded gasoline" ( page 450) or the Factory Approved Service Products pamphlet. i Leaving the engine running and the fuel cap open can cause the ú malfunction indicator lamp (USA only) or the ± malfunction indicator lamp (Canada only) to illuminate. More information can be found in the "Practical hints" section ( page 356). Overfilling of the fuel tank may create pressure in the system which could cause a gas discharge. This could cause the gas to spray back out when removing the fuel pump nozzle, which could cause personal injury. Replace fuel cap by turning it clockwise. You will hear when the fuel cap is tightened. Close fuel filler flap. 306