2008 Mercedes R-Class Owner's Manual - Page 541

Technical data Fuels, coolants, lubricants, etc. Fuel requirements Gasoline engine Only use premium unleaded fuel. The octane number (posted at the pump) must be 91 min. It is an average of both the Research Octane Number (RON) and the Motor Octane Number (MON): (RON+MON)/2. This is also known as the ANTI-KNOCK INDEX. Unleaded gasoline containing oxygenates such as ethanol, IPA, IBA and TBA can be used provided the ratio of any one of these oxygenates to gasoline does not exceed 10%; MTBE must not exceed 15%. The ratio of methanol to gasoline must not exceed 3% plus additional cosolvents. Using mixtures of ethanol and methanol is not allowed. Gasohol, which contains 10% ethanol and 90% unleaded gasoline, can be used. These blends must also meet all other fuel requirements, such as resistance to spark knock, boiling range, vapor pressure, etc. Diesel engine Only use commercially available vehicular ULTRA-LOW SULFUR HIGHWAY DIESEL FUEL (15 ppm SULFUR MAXIMUM). To prevent malfunctions, diesel fuel with improved cold flow characteristics is offered in the winter months. Check with your fuel retailer. Gasoline additives (gasoline engine) A major concern among engine manufacturers is carbon build-up caused by gasoline. Mercedes-Benz recommends only the use of quality gasoline containing additives that prevent the build-up of carbon deposits. After an extended period of using fuels without such additives carbon deposits can build up, especially on the intake valves and in the combustion area, leading to engine performance problems such as: Warm-up hesitation Unstable idle Knocking/pinging Misfire Power loss ! Do not fill the tank with gasoline. Do not blend diesel fuel with gasoline or kerosine. The fuel system and engine will otherwise be damaged, which is not covered by the Mercedes-Benz Limited Warranty. 540