Mercedes and Octane Requirements - PeachParts Mercedes-Benz Forum

MB-Dude · #1 09-13-2007, 11:21 AM

While doing a little research for my posts in the thread Mercedes & Gasoline (http://www.peachparts.com/shopforum/showthread.php?t=199694), I ran across this information as to octane requirements in MB gasoline engines. I pass it along so folks will know that not all pre-1986 MB gasoline engines *require* premium gasoline.

{From the Factory Approved Service Products September 2006 bulletin, pages 7&8}

Gasoline Engines
Reformulated gasolines (RFG) and/or unleaded gasoline containing oxygenates such as Ethanol, TAME, ETBE, IPA, IBA, and TBA can be used provided that the ratio of any one of these oxygenates to gasoline does not exceed 10%. MTBE may be added up to 15%. The ratio of Methanol to gasoline must not exceed 3% plus co-solvents.

Mixtures of Ethanol and Methanol must not be used. Gasohol, which contains 10% Ethanol and 90% unleaded gasoline, can also be used. These blends must also meet all other fuel requirements such as resistance to spark knock, boiling range, vapor pressure, etc.

Gasoline Additives
Of major concern among various engine manufacturers is the carbon build-up caused by gasoline. MERCEDES-BENZ recommends using only 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, and
• power loss.

In areas where carbon deposits may be encountered because gasoline with additives are not available, Mercedes-Benz recommends the use of additives approved by us for use on Mercedes-Benz vehicles (page 15).

DO NOT blend other fuel additives with the fuel. These additional additives only result in unnecessary cost and may be harmful to engine operation.

Damage or malfunction resulting from poor fuel quality or from blending additional fuel additives other than those tested and approved by us for use on Mercedes-Benz vehicles (page 15) are not covered by the Mercedes-Benz Limited Warranty or by any pre-owned or Extended Limited warranties.

Premium Unleaded
Use only premium unleaded gasoline meeting ASTM standard D439. The octane number posted at the pump must be at least 91 min. In the U.S., this octane number is an average of the Research octane number (R) and the Motor octane number (M): (R + M) / 2. The octane number is also known as the Anti-Knock Index.

As of model year 1987
All gasoline engine models require premium unleaded gasoline.

Model year 1986
All gasoline engine models, except the 190E 2.3 require premium unleaded gasoline.

Model years 1975 - 1985 and model year 1986 190 E 2.3
Use unleaded regular gasoline meeting ASTM standard D439. The octane number posted at the pump must be at least 87 min.

Model years 1972 - 1974
Use leaded or unleaded gasoline meeting ASTM standard D439. The octane number posted at the pump must be at a minimum of 87. When only unleaded gasoline is being used, check the valve clearance on engines with mechanically adjustable valves at half the recommended interval.

Pre-model year 1972
Use premium unleaded gasoline meeting ASTM standard D439. The octane number posted at the pump must be at a minimum of 91. Check the valve clearance at half the recommended interval.

Flexible Fuel Vehicles
Flexible Fuel Vehicles - As of Model year 2003 - 2005
Use premium unleaded gasoline (see gasoline engines) or Ethanol (E85) fuel to operate Flexible Fuel Vehicles. Models capable of operating with E85 are identified by a label reading Premium gasoline or E85 only! on the fuel filler flap. For information on Flexible Fuel Vehicle operation, refer to the Operator’s Manual.

{End of bulletin excerpt}

With the except of MB’s stance on gasoline additives (2001-no, 2006-yes), this information is very consistent with the same section in Factory Approved Service Products November 2001 bulletin, suggesting there has not been a change in their view of octane requirements.

Cheers,
Jeff