I am a bit OCD on MPG and have only used one tank of fuel in my new C180 auto.
First if all, this is a 1.6l engine, not 1.8 as someone posted on page 2.
I am coming from a 318 BMW that consistently put out 33MPG on mostly town trips. The on board computer was very good at calculating true MPG and matched my own calculations.
I have been driving my new C Class on Eco gears, not much Air Con, and with annoying StopStart switched off. Driving for economy it returned only 30mpg, which disappointed me to be honest.
In about every respect I prefer this engine to the 2litre in the 318, but it is clearly going to be thirstier, and driving normally with a mix of frugal and fun is obviously going to be well under 30mpg.
Personally I can live with that because as a package this car beats my outgoing 318, but I can't say I'm not disappointed with the economy.