Dick - many here have reported better overall mpg from their 420-SELs than their 300-SELs. I'm not too surprised by that. The 300-SELs turn 3400 rpm at 70mph. All of my Asian cars are in the 2500-2700 rpm range at same speed. MB had to spin the motor faster on the 300-SEL to keep it from being a complete dog. The higher rpms drink more fuel.

My driving is primarily highway - get around 20mpg-22mpg on avg using 93 octane. Some report that 89 octane works well in 103 motors. I tried it and felt it ran better on 93 octane. Opinions vary here.

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Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"