Fuel efficiency
 

I bought a W204 2013 demo-model C200 avantgarde "blue efficiency" (turbo) petrol auto from a dealer about a year-and-a-half ago as an "upgrade" to my 2005 W203 C180 kompressor manual.

My W204 auto is a 135 kW 1.8l model as opposed to my ex 115 kW 1.8l has C180 manual. To be honest the C200 has more punch but it is overkill in everyday driving (for me at least).

The C180 returned 9l/100km on a tank on my normal commuting cycle and 7.3l/100km at a steady 120km/h on the open road.

The C200 returns 10l/100km on the same commuting cycle and 8.3l/100km at a steady 120km/h on the open road.

In the old days I would have expected auto boxes to be heavier on juice than manual boxes. But my impression from what I read was that the 7-speed box is actually lighter on fuel than a manual six thanks to more optimal shifting. At a steady 120km/h the auto/manual difference should be negated I thought. Seems like I was mistaken.

One would expect a 135kW unit to be less efficient than a 115kW unit. Unfortunately I erroneously thought that the difference would be made up by the move away from the old kompressor technology to the new turbo blue efficiency engines. Seems like I was mistaken again.

Furthermore the manufacturer's consumption figures are clearly just ugly black lies. Even what you read in the renowned Car Magazine (my favourite!) does not match what I experience in real life.

Anybody that can shed more light on this issue?

There seems to be little rhyme nor reason to fuel economies today. I just traded up to an S 450 from a CLK 500 cabriolet. The CLK was obviously smaller and lighter with the same transmission. The reality is that I'm getting better fuel economy in the S series than with the CLK. With the S series I'm getting as high as 8.5 per 100 at a speed controlled 120 to 125 ish speed. With the CLK under the exact same circumstances (same highway, same general climatic conditions and same driver) I could never do better than 9.5 per 100 ish. I don't know why but I sure am enjoying over 1000 km per tank mostly highway driving. So far I love this 4.7 litre engine.