The Mercedes CLK320 CDI won't be everyone's cup of tea but if you like your coupes big and powerful, this impressive V6 diesel should do nicely. This marque of car tends to suffer from the usual coupe complaint that it is neither a sports car nor a genuine four seater with the result being somewhere between the two. The Mercedes CLK320 CDI, however, would appear at first glance to have a lot more to offer.

Let's start with that astonishing powerplant. Unlike old Mercedes diesels, which were rather lumpy five-cylinder units, this latest is a creamy V6 with four valves per cylinder. Rated at a healthy 224bhp, it's got more than enough muscle to haul the elegant Mercedes around. What's more, it will reach its maximum torque figure of 510Nm at little more than tick over and sustain it across a broad plateau from 1,600 and 2,800rpm. This common rail direct injection engine has quickly proved a winner for the Daimler Chrysler group and it's being plumbed into all manner of Mercedes and Chrysler models to great effect but the CLK vies with Mercedes' CLS 'four-door Coupe' for being the most attractive vehicle to use the 3.0-litre unit.

Slotted beneath the low-slung bonnet of the CLK Coupe (you can't get it in the Cabriolet version), this engine will punch the car to 60mph in a smidgeon over seven seconds and on to an electronically limited top speed of 155mph. Combined fuel economy is rated at 36.7mpg which is little short of astounding given the size, weight and performance of the car. The CLK320CDI excels as a long distance cruiser, capable of notching off relatively huge distances between refuelling stops.

More impressive than the largely irrelevant performance figures is this car's real world performance through the gears.

The prodigious torque figure isn't far off that of a V8 petrol-engined CLK500. And fuel consumption of course, as we've said, is in a different league.

Unlike its smaller C-class Sports Coupe counterpart, the CLK is a proper four-seater and appeals to a more mature audience, Mercedes producing figures which indicate that the average age of CLK owners hovers around 50. It's a car that's perfect for the affluent mature buyer - smooth, luxurious, safe, good looking and with the right badge on the bonnet. There are those who claim that the latest generation CLK isn't quite as elegantly alluring as its predecessor, but beauty is in the eye of the beholder.

Compared to a BMW 3 Series Coupe or an Audi TT, the latest generation CLK feels a more grown up proposition, giving credence to the company's ownership demographic data. That's not to say its future was always quite so assured. The original version was in danger of being squeezed into irrelevance by Mercedes own product planning policies. The introduction of the C-Class Sports Coupe did for sales of entry-level CLK models, whilst the SLK and SL models made opting for upspec CLKs an act of intense soul searching. In second generation guise, many of these issues have been addressed and equipped with this impressive diesel, the CLK320 CDI more than justifies its existence.

In recent times, further efforts have been made to make this car even better to drive. As well as the adoption of the new engine, these efforts have included the adoption of what Mercedes dubs 'Direct Control' technology. This amounts to modified axle bearings, more direct steering and a shorter gearshift travel, offering a sportier, more dynamic feel to the car. Likewise, optional steering wheel gearshift buttons for models with an automatic transmission, revised audio units with Europe-wide navigation and bi-xenon headlamps with cornering light function have also been introduced. Stung by criticism of so-so interior quality, Mercedes have also taken steps to redesign many of the CLK's switches and controls. Trim changes include a redesigned front bumper and radiator, plus a smarter fascia for Avantgarde-trimmed models.

The body is a full 40% stiffer than the first generation CLK model which has allowed the engineers to get rid of the centre pillar between the front and rear windows, a design cue that harks back to classic Mercedes coupe models of the Sixties and gives this Mercedes a uniquely elegant appeal.

Inside, the improvements for second generation models are small but again, very significant. Where some of the trim in the original version felt a bit down-market, this car has much more in common with the larger S-class-based CL coupe and, like that model (but unlike the C-class Sports Coupe), can easily seat four adults in long distance comfort. The longer, wider and taller shape helps here, as does the decision to get rid of the central rear seat (instead there's a storage tray) and concentrate on pampering just two rear passengers properly. All models now come with climate control for the air conditioning, automatic headlamps with washers, all-round electric windows, rain-sensing wipers, a height and reach-adjustable steering wheel, 'Speedtronic' cruise control, twin front, side and window airbags, plus of course ABS with Brake Assist and the ESP stability control programme. There are three trim levels - plush Elegance, trendier Avantgarde and Sport.

With the CLK320 CDI, Mercedes have created the perfect match between chassis and power unit. The super smooth V6 diesel engine pulls all the way in a delightfully reassuring manner providing four full-size adults the ability to recline in true Mercedes-Benz comfort. Many in the past have tried to create the perfect coupe. It could be that with the CLK 320 CDI, Mercedes have finally cracked it. Now, all Mercedes needs to do is to import the Cabriolet version.