1000km Road Test - Mercedes-Benz S320 CDi

Value for money

Pricing

The S320CDi costs $198,810. It shares base model status in the S-Class range with the S350 3.5 litre V6 petrol-powered model.

Warranty

Three years/unlimited kilometres.

Standard equipment

The S320 includes leather upholstery, power adjustable, heated and ventilated front seats, front and rear parking sensors, bi-xenon swivelling headlights, six stack in-dash CD/DVD/MP3 compatible player, eight airbags, automatic dual zone air, DVD navigation, digital/analogue TV tuner, voice activation, cruise control with speed limiter, sunroof, rain sensing wipers, active front seat head restraints, tyre pressure monitoring and 17 inch alloy wheels.

Selected options

It would take the entire page to list them all. Distronic Plus adaptive cruise control $4153; air seats (front or rear) with massage function $3728; night vision $4153; reversing camera $1600; rear seat entertainment system $7998.

Retained value

This is the first S320 diesel model. A 2005 W220 S350 V6 petrol retains 43-47 per cent of its new price as a trade in, according to industry valuer Redbook.

Design and function

Technical details

• The S-Class traces its lineage back nearly 50 years to the 1959 "tailfin" model.
• The current model was introduced in 2006.
• The 3.0 litre V6 turbodiesel engine uses common rail direct injection with piezo injectors that can deliver five injections per power stroke at pressures up to 1600 bar, with injector needle jet movement controlled to within thousandths of a millimetre. 
• The turbocharger has electronically adjusted turbine blades.
• Exhaust gas recirculation, two catalytic convertors and a maintenance free particulate filter minimise nitrogen oxide and particulate emissions.
• The 3.0V6 is a long stroke engine that produces 173kW of power at 3600rpm and 540Nm of torque from 1600-2400rpm.
• It's matched with a sequential seven speed automatic transmission, with gear selected electronically, using a lever on the right of the steering column. 
• Suspension is independent multilink, with air springs and adaptive dampers.
• 17 inch alloy wheels are fitted with 235/55 tyres. Our test car used optional 18 inch wheels with 255/45 (front) and 275/45 (rear) tyres.
• The S320 weighs 1955kg.

Ergonomics

When it introduced this S-Class in 2006, Mercedes returned its flagship to the traditional limo formula - thick, heavily textured, stitched trim, dark tones, aromatic leather, polished timber veneers, chrome and shag pile - to make the cabin once more feel like old money. It did the same with the C-Class in 2007.

The finishing touch in the S is an elegant analogue clock in the centre of the dash.

Power adjustable, heated and ventilated front seats are the last word in comfort. If you drive long distances, they are superb. If you get driven to work, the back seat is equally sumptuous, and of course there is no shortage of leg room.

Although the S-Class feels enormous when you first climb into the driver's seat, the control layout is easily learned. The wand-style gear lever, on the right of the steering column, has no intrinsic advantage over a conventionally located lever, but that's the luxury car business for you. Logicality is irrelevant.

Mercedes has joined BMW and Audi in replacing its squillion button COMAND system with a cursor/screen arrangement to control the audio, TV, CD/DVD, phone and navigation. It's intuitive, easy to use and the screen is clearly legible; many functions can also be operated with a simplified version of the multi-function wheel controls, and monitored by a display on the instrument panel, in front of the ingenious "virtual" speedo.

There's plenty of storage close to the driver, including a large centre console bin. Vision is OK, but the side mirrors could be larger.

The boot has a long, narrow, shallow floor with no extendibility, a couple of handy shopping bag hooks and small nets on each side. A full sized alloy spare is under the floor.

Safety

• Although it has not been tested by EuroNCAP, you can assume with 100 per cent certainty that the S-Class would score five stars.
• As Mercedes' flagship sedan, the S-Class has introduced many safety features to the market, including the passenger safety cell, crumple zones (both premiered on the 1959 model), seat belt pretensioners, anti lock brakes, traction control, stability control and airbags.
• The current model takes safety technology to a new level, although some of it is simply showing off.
• The car itself can actually assume functions until now performed by the driver.
• The optional night vision system, for example, uses two infra red lamps in the main headlamp housings to illuminate the road with invisible infrared light. The image is captured by a camera on the windscreen, then viewed as a greyscale image on the instrument panel. It's of no practical value, because it cannot be safely used while you're driving. Watching an image instead of the real road ahead is not a good idea. This particular piece of safety "engineering" is actually nothing more than a gimmick.
• The optional Distronic Plus cruise control system automatically maintains a gap between your car and those you are approaching. It will automatically bring the S to a complete stop if necessary to avoid running into a car in front.
• Brake Assist-Plus, like Distronic, uses radar to calculate the optimum braking distance in an emergency and automatically applies the required pedal pressure to - hopefully - stop safely.
• While this is happening, Pre-Safe - which debuted on the previous S-Class - gets the signal that you might be in a bit of bother and automatically tensions the seat belts, adjusts the seats to an upright position and closes the sunroof - in preparation for impact.
• If the big bang occurs, Post-Safe switches off the engine and fuel pumps, unlocks the doors and lowers the windows. If you're in deep trouble, front and rear pillars have marked cutting points for rescuers to get to you.

Security

The S-Class has not yet been rated by NRMA Insurance.

Build and finish quality

The S-Class is luxurious and opulent, of course, and the quality of materials is commensurate with its price. However it's a long car, and despite its size and weight there is some body flex on rough roads, which also prompt a few chirps and squeaks in the cabin. Mercedes quality and reliability record in independent owner surveys has also been patchy for the past five years or so.

On the road

Fuel efficiency

• In the Australian standard test, the S320 averages 11.6L/100km in town, 6.4L/100km on the highway and 8.3L/100km combined.
• CO2 emissions are 220g/km.
• The S320 scores three stars out of five in the Green Vehicle Guide.
• In our 1000km test much of the driving was on the open road, where across a range of speeds and conditions the S320 averaged 7.5L/100km, which is amazing for such a big, heavy car. It has a 90 litre tank, so a range of up to 1200km is possible.
• It's worth noting that Mercedes has just introduced an even more fuel efficient S320 in Europe, called the Blue Efficiency model. It has fuel saving features like an on-demand, electrically driven power steering pump, decoupling of the automatic transmission's torque converter as the car comes to a stop, and low rolling resistance tyres. The S320 Blue Efficiency averages 7.6L/100km and produces 199g/km of CO2.

Performance

In a super sized car that weighs nearly two tonnes, the 3.0 litre V6 turbodiesel delivers acceptable performance in the context of real world roads and speed limits.

In terms of outright acceleration, the diesel is comparable with the 3.5 litre V6 petrol S350. It takes 8.5 seconds to drive the big S to 100km/h. The 5.5 litre V8, which we tested earlier, took 6.6 seconds.

Mercedes offers the S in Europe with a 4.0 litre V8 diesel, which produces 235kW and 730Nm. Shame it's not available here.

Still, the 3.0 litre is a fine engine, with more character than your average diesel, too. It sounds a bit like an old Falcon under load; once you reach cruising speed, though, it's very smooth and quiet.

The S320 has a typically lazy Mercedes accelerator, so you have to give it a bit of a shove to get good responsiveness from a standing start. On the move, though, a gentle squeeze releases vast amounts of torque, giving the S320 effortless performance in all situations.

The seven speed auto uses a small wand on the right of the steering column as the lever. It has Comfort, Sport and Manual shift modes, the latter operated by buttons on the back of the wheel. Sport mode also adjusts the air suspension to a firmer setting.

The seven speed shifts smoothly, and lets the engine rev to 4000rpm or so before it changes up. Manual mode is redundant; the timeliness and refinement of the shifts are fine in Comfort or Sport mode, though quite slow in the context of the latter. When crawling along in traffic, downshifts were occasionally a bit clunky as the car rolled to a stop.

Handling, steering and braking

The S-Class takes a while to get used to because it's a big, intimidating machine. In tight corners, it's no sportster. However on the open road it does what a Mercedes-Benz should do - gains your confidence, then rewards it with precise steering, and the highest levels of stability and confidence.
 
Sport mode is preferable on the open road, where Comfort mode is a touch loose and can transmit some road shock, giving the body a shake. Sport mode exercises tight control over body movement, produces more secure roadholding, and still provides a comfortable, compliant, quiet ride.

The test car was fitted with optional 275/45 (rear) and 255/45 (front) tyres on 18 inch alloys, and the ride was much more absorbent than on the S500 tested earlier, which had 19 inch wheels and 40 aspect ratio tyres.

Comfort mode is the way to go in town, where it's exceptionally smooth and supple.

The steering is light and precise, albeit with Mercedes' usual lack of feedback, and a hint of kickback on very choppy surfaces.

The brakes have ample power and a more responsive, firm pedal than usual from Mercedes. Hit it hard and the S320 pulls up fast.

Smoothness and quietness

No problems at all here. Few cars can emulate an S-Class's hushed cabin.

Summary

The S-Class is the car that made Mercedes reputation and sets the standard in this class. The current model is the best for some time. The S320, like any luxury limo, is indulgent, but that's why people buy these cars. The fact that it returns better fuel consumption figures than a Camry allows you to enjoy yourself with a clear conscience.

BMW has a new 7 Series due for launch in 2009, though at the time of writing with no diesel engine in the Australian model lineup. This may change, given the growing popularity of diesel.

Audi's ageing A8 has 3.0 litre V6 and 4.2 litre V8 diesels, but in this class the S320, for the time being at least, really is in a class of its own.

Test by Bill McKinnon, November 2008.

The writer of this report does not necessarily represent the views of the NRMA and this report is provided for you as an alternative to our own NRMA car reviews.