Why can't my wife's Mercedes-Benz A160 compete with my Audi A4 for fuel economy?

My wife and I drive between West Cornwall and Ealing, 570 miles return with all but 10 miles on motorways and dual carriageways, cruising at an indicated 75 mph in an Audi A4 3.0 litre diesel Quattro Tiptronic, which returns between 40 and 44 mpg according to the fuel computer. We have just done the trip in my wife’s new Mercedes-Benz A160 auto returning only 34.8mpg. It was a straight run in good weather with no hold-ups. Should we have achieved better?

Asked on 5 March 2011 by DK, Ealing

Answered by Honest John

You have experienced the difference between a big, powerful engine running at very low revs and a small, far less powerful engine trying to keep up. Most of the increased consumption will have been on cruise control while ascending inclines.

Tags: fuel economy real mpg

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