Before its UK launch in April 2009, we were given the opportunity to test drive a the new CDI to see how it fared against the petrol version.
At 88g/km of carbon, this car is the most 'green' production car in the world and is hoping to make a real impact on on the UK market.
Externally, it bears all the same characteristics of the petrol 451.
Inside, the car looks pretty much the same as a petrol. It is even possible to upgrade all the standard parts with upgraded, or even Brabus parts.
However, all CDIs come complete with pods as the rev counter has a slightly different scale compared to the petrol.
But the real difference is under the engine cover. The Mitsubishi engine of the petrol model is now a Mercedes 800cc direct injection diesel with a pleasant return of the Mercedes-Benz emblem. This tiny block can delivery 33kW (45bhp) of power with 110Nm of torque.
Space is now at a premium!
So how does it drive? Well, given how 'clattery' the 450CDI was, I was sceptical. As you sit inside, you only really notice that it's a diesel when idling. This is by no means intrusive. However, as soon as you put your foot down, the 'torque'y engine pulls you away quite nicely.
When out on the motorway, there is no problem reaching 70mph (and above!) and it is quite easy to forget it's a diesel. Then you remember you are getting around 80-88mpg, and your wallet breathes a sigh of relief.
As you accelerate hard from stand still, there is considerable torque as you start but this seems to pull back around 30mph - possibly electronically limited. As with all diesels, the torque dies off rapidly as you approach the redline.
But, as an efficient city car, we were impressed. It will be interesting to see what modifications are possible and the question on a few people's lips is 'What about remapping?'. We'll be interested to see...