You won't get anywhere near 30mpg, but you can expect high 10's low 20's depending on your foot. 29mpg from the 400E on the freeway....was it going downhill all the way? After 7 years reading w124 boards consistently I have never heard anybody getting that type of mileage.

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2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
2014 Jeep Wranger Unlimited Sahara - 62k
2003 Gray Mercedes ML350 - 122k