Sedan Ramblings - Reviews, comparisons and all things sedans

Diesel Luxury Sedans - What's the Point? (16/12/00)
by Traian Popescu

It seems no one in the world is unaware of the skyrocketing fuel prices. Even in the US people complain, where fuel rates are only a fraction of those found in Europe. In Canada, a person driving 25,000 km (15,625 miles) in a year with a car that gets 17 mpg consumption will pay in the neighbourhood of $3000 CDN only for gas. The new trend, which seems to have caught on in Europe, is diesel. True, the general assumptions that diesel engines are noisier than their gasoline counterparts and provide poorer performance are true, to a degree. So why in the world would any manufacturer build a luxury sedan powered by a diesel engine? How could it overcome those flaws? Read on.

The newcomers in this previously non-existent category are the Mercedes S320 and S400 CDI. The smaller brother uses a 3244cc inline-6 engine that produces 197 horsepower and a mammoth 346 lb-ft of torque at 1800 rpm, even more than the gorgeous S500, which only serves up 339 lb-ft at a higher rpm. Result: the S320 CDI easily accelerates as well as the V6 "petrol" powered S320, even better actually considering the responsiveness provided by the low-end torque. The only way to tell the two cars apart is the deeper engine note exerted by the diesel model with the pedal to the metal. Outside, there is more racket than a gasoline model, but the sound-deadening material that seals the cabin filters almost any extra noise out.

In the UK, one of the countries where Mercedes markets its diesel sedans, the price for a S320 CDI at 45,840 GBP is actually 3,300 GBP cheaper than that of its gasoline sibling. Considering that the CDI also gets a fuel economy figure of 35.5 mpg over the combined cycle, compared to 24.6 for the S320, the savings really start to add up after a while. And the performance is virtually identical: the S320 CDI reaches 62 mph in 8.5 seconds and continues to a top speed of 141 mph.

Of course, all the standard S-Class goodies are still there. The gorgeous design, inside and out, AIRmatic air suspension and adaptive damping system and all the on-board computers and stereo speakers anyone could wish for are all present.

Next up on the food chain is the S400 CDI. Usi ng a 3996cc V8 powerplant, it develops 250 horsepower at 4000 rpm and an astounding 413 lb-ft of torque at 1700 rpm. The engine is a 32-valve unit and uses VNT (variable nozzle turbine) twin-turbochargers. To reduce the mass, the engine bloc is cast from aluminium and correspondingly the whole unit weighs only 510lb (245 kg).

The outcome is a trip to 62 mph that takes only 7.2 seconds, a time that is identical or possibly even a couple tenths quicker than its gasoline counterpart, the S430, and a top speed of 155 mph.

Through the various feats performed by the German engineers, including balancing techniques to reduce vibration and better sound-deadening material, noise levels are actually lowered to the point where they are fitting for a true luxury sedan. Not only that, but the S400 CDI achieves an average consumption rating of 25 mpg, compared with about 19 mpg for the S430. And we all know diesel fuel is less expensive as well, right?

Considering that the excessive noise syndrome of typical diesel cars is solved and performance differences are non-existent between them and their gasoline counterparts, the tables have finally started to turn and it is the latter group that will have to play catch-up. Better fuel mileage and an unbelievable torque curve should become the trademarks of diesel engines, rather than the unfavourable labels they were given before. The only problem remaining is this: are Mercedes and other luxury sedan manufacturers providing answers to a question no one is asking? Will a person who spends nearly 50,000 GBP on an automobile be willing to overlook the bad rap diesel vehicles have held in the past in order to save some money? Nevertheless, while in a way it pains me to say this, and there will of course always be the snobs who will never admit it, the S320 and S400 CDI are actually better all-around cars than their S320 and S430 counterparts.

© Traian Popescu , World's Fastest Sedans (http://www.fantasycars.com/sedans/), 2000.

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