My A-Class is just coming up to 100,000 miles, and returns 70mpg on a long open motorway run, 60mpg or better on the open road.
It's the same 4 cylinder 2 litre unit you get in all the A and B Class cars, they just set the engine management system to give different power outputs. I think mine is about 110HP
What's wrong with it? poor ground clearance, especially over speed bumps, and the fact I didn't get a tow bar fitted when I bought it...
