Does Shell Optimax Unleaded work for MB?
I’ve used Optimax in a 1993 E280 W124 with an improvement from 10l/100km to just under 8 on long runs and from 13 to about 11 in the city. In general, Optimax offers gains where the engine management system includes a knock sensor to take advantage of the higher octane rating (98RON vs 95 or 91 here in Australia) and/or a feedback loop which corrects the mixture to run at optimum mixture or can meter the fuel injected by mass. The latter requirement is needed to take advantage of the higher specific gravity (0.78 vs 0.72 for ordinary unleaded) by reducing the volume of fuel injected to get the same energy input. And we measure our fuel economy by volume not mass, so we get better mpg or l/100km for the same volume of denser fuel. Cars without the above features rarely gain from using Optimax or similar higher octane and density fuels, eg absolutely no difference in economy with an early Land Rover Discovery. Be interesting to see how an old high performance carby engined car (Cooper S
