Changes to the Mercedes CLS line-up bring new diesel options, but they are still not as stylish as their relations, writes Michael McAleer, Motoring Editor.
The dreaded diesel rattle was once anathema to any vehicle that didn't tow a silage trailer or come with a four-wheel drive system capable of conquering Carrantuohill.
Nowadays we're finding diesel engines creeping into the small car market and even making occasional forays into sporting coupés.
Here we are behind the wheel of the current premium market trendsetter, Mercedes' four-door coupé CLS, while up front, a 3-litre diesel engine putters away. Putters is more a figure of speech, for it manages 0-100km/h in 7 seconds and offers up enough torque - or pulling power - to beat all other engines in this model range save the flagship CLS63 AMG.
The fact that few would raise an eyebrow to the inclusion of a diesel derivative to the CLS range demonstrates just how far diesel has come in recent years.
When Audi introduced a diesel offering for its A4 convertible two years ago, many gawped at the contradictions involved. Surely, the thinking went, something as image conscious as a convertible should never be saddled with a dirty diesel engine.
In truth, there was nothing dirty about the diesel. It's strictly an outdated prejudice, up there with other snobbish pretensions about Japanese cars being cheap knock-offs.
Things have dramatically changed in the last five years. A diesel-powered car has won the last two Le Mans 24-hour races. Over at BMW, its 3-litre diesel engines offer as much fun to drive as its legendary straight-six cylinder petrol range, while Audi looks set to introduce a diesel version of its R8 supercar in the next few years.
The fact is that diesel is now as viable an option in all ranges of car as the petrol equivalent. The common-rail set-up devised several years ago makes a well-built diesel engine as flexible, and arguably more potent, in everyday driving than its petrol equivalent.
Admittedly the Germans have long been advocates of diesel technology.
They appreciated the mix of torque - even if it is rather limited to short spurts - with good fuel economy. That's understandable if you're travelling the 600km from Munich to Hamburg on the autobahn.
It's only natural, therefore, that the Germans have been keen to push out the boundaries of acceptance for diesel technologies. While they're reluctantly getting into the petrol-electric hybrid market following the successes of Toyota and Lexus, their heartfelt belief remains that diesel is the best short-term option for the future; at least until a viable hydrogen fuel cell vehicle comes on stream.
Hybrids may make sense in heavy town traffic, but out on the autobahn, even hybrids run almost entirely on their petrol engines and that's where diesel engines have their beating.
This is the latest 3-litre diesel engine from Mercedes, introduced in the CLS as part of an overall engine revamp of the model line-up.
The revamp comes nearly three years into the four-door coupé's lifecycle and is largely due to engine advances made during the development of the new flagship S-Class range. The time has come to pass these improved engines down to other Mercedes models.
It's a timely update for a model range that still looks as avant-garde as it did the day it was unveiled.
The idea of creating a four-door coupé was around for some time, but few have mastered it.
Citroën has often claimed that early models like the 1970s SM and even the CX were in fact family cars with coupé styling, but few buy these lines.
What Mercedes created instead was a car that offered saloon interior space - albeit with room for two passengers in the back rather than three - with sleek coupé lines.
If ever Mercedes needed reassuring that the idea worked, they need only look at how they caught the rest of the market on the hop.
No sooner had CLS hit the market than orders came down to the design departments of several car firms to create something similar.
In the next year or so we can expect three new additions to the four-door coupé market: Porsche's Panamera, a VW Passat coupé and a production version of BMW's gorgeous CS Concept, likely to be launched as the new generation of 8-Series.
That others may follow Mercedes down this route is perhaps the greatest vindication for the engineers who persevered with the four-door coupé project against undoubted cynicism from some within the brand.
The CLS is meant to sit between the E-Class and the S-Class. It also served as something of an exterior design study to test the water for some of the minor styling markers that came with the new S-Class, launched some time later.
As you can probably guess, we still love the styling of the CLS. Despite it's relative age, it managed to garner admiring glances and, when parked in a leafy suburb on Dublin's southside, it attracted as much attention as neighbouring Porsches.
So would we still recommend it as the flexible coupé alternative to the S-Class?
The answer to that is less clear-cut than it was when this car was first introduced.
When Mercedes opted to revamp the engine range to bring it into line with the S-Class, it could just as easily have revamped the interior as well.
After all, it introduced the new interior styling to the recently launched CL range and the end result is a car that's one of the best Mercedes has built in years.
YES, THE NEW ENGINE RANGE in the CLS is impressive and those extra 40Nm of torque will make a difference the next time you are trying to power away from that dodgy taxi driver who seems intent on weaving into the side of your car.
And yes, those smart sweeping lines and the uniquely styled rear end still catch many admiring glances as you work your way through traffic.
Yet sitting behind the wheel doesn't offer the same feeling of premium that one would expect from a car that starts at nearly €90,000 before you start to add on a few creature comforts.
The interior trim is, in effect, the same as the E-Class and that's not good enough for a car that's often pitched as an alternative to the S-Class.
There is also some inexplicable scrimping on detailing as well, such as the lack of proper lining on the inside of the boot and the tinny sound it makes when you close it.
We've heard a more premium clunk from Fiat Pandas we've tested in the past.
If we hadn't thought so highly of the new S-Class and if we hadn't been wowed by it's stylish switchgear, it's soft ambient lighting and the feeling of luxury about the whole package, then perhaps we would not be so put out by the fit and finish of the CLS. Even the "matt burr walnut" started to annoy us in the end.
It is wood veneer, but it does a great imitation of that faux plastic wood you find in Korean cars trying to pretend to be premium models.
In terms of performance, the new 3-litre impresses, but it's not at the same performance level as its direct diesel rival from BMW, which offers 280bhp and 580Nm of torque compared to 221bhp and 540Nm for the Mercedes.
It's suspension is also aimed more at comfort than performance handling, something that may not be quite in tune with the desire of potential coupé owners.
Steering remains lighter and less informative than rivals like the BMW 6-Series but it's a good package all round.
On some of the tight country roads it felt as wide as it is and that didn't lend itself to a relaxed drive, but on our growing motorway network, the car was in its element.
Those looking for a more focused drive will still opt for rivals like the 6-Series.
However, while the BMW has its beating in terms of performance and driving dynamics, there's a hefty €15,000 premium to be paid for the BMW 635d diesel over this CLS 320 CDI.
That's a significant advantage for the Mercedes that also has the flexibility of those extra rear doors and arguably more impressive exterior styling.
The CLS remains one of the best buys in the Mercedes family, after the S-Class and the fantastic CL. That's perhaps why we were so disappointed with the fit and finish.
When it launched the new S-Class, the three-pointed star began to really shine once more after a few years in the doldrums. The new CL stole our heart.
This revamped CLS retains its elegant look, but the mid-life changes aren't enough to persuade us from recommending owners to look first at the S-Class or 6-Series.
Hopefully a full revamp is in the pipeline, one that will bring the car into line with its S-Class sibling and ready to face what's likely to be a premium market punch-up with BMW's upcoming 8-Series.
ENGINE: A V6 2987cc common-rail diesel engine putting out 221bhp @ 3,800rpm and 540Nm of torque between 1,600rpm to 2,400rpm.
SPECIFICATION: Standard features on CLS include; front side and window airbags; anti-lock brakes (ABS); brake assist; electronic stability programme (ESP) with anti-skid control; 17" alloys; auto headlights; silk-matt burr walnut wood trim; automatic climate control; cruise control; six-stack radio/CD.
Optional extras on the test car included: metallic paint (€1,976); leather interior (3,240); parktronic sensor system (1,563); wool/leather steering wheel (1,236); heated front seats (816).
OFFICIAL L/100KM (mpg):
Urban: 11.0 (25.7)
Extra-urban: 6.4 (44.1) Combined: 8.1 (34.9)
CO2 emissions: 215g/km
Annual motor tax: 1,109
Price: 86,260 starting price for CLS 320 CDI