2024 Mercedes-Benz S450d Driven: Forbidden Fruit Writ Large

As it happened, I'd just driven an S450d 4Matic some 230 miles from Stuttgart down into the Swiss Alps. Much of the drive had been on German autobahn and Swiss motorway, though the last 30 miles had been on roads that wriggled and writhed through the mountains. A lot of the autobahn and motorway running had been through lashing rain and high winds, and snow was falling heavily as we climbed the 7,493-foot Julierpass and snaked down into St. Moritz. But the big Mercedes had felt utterly imperturbable through it all.

Launched in late 2020, the W223-series S-Class debuted the rear-drive vehicle architecture known internally at Mercedes-Benz as MRA2, which now also underpins the recently launched W214-series E-Class sedan and All-Terrain wagon models. Effectively an evolution of the hardware that supported the previous generation S-Class, MRA2 was engineered under Hubert Schneider's direction to package a new rear-steer axle to improve low-speed agility and a larger battery pack to give plug-in hybrid models longer range on pure electric power. The wheelbase was increased by two inches to 126.6 inches, and overall length went up by 1.3 inches to 208.2 inches. Width grew by 2.0 inches, and height increased by 0.4 inch.

Though U.S.-market Mercedes-Benz S-Class models are restricted to three powertrain options: the 3.0-liter inline six and 4.0-liter V-8 mild hybrids in the S500 and S580 models, and the six-cylinder plug-in hybrid in the 510-hp S580e. The S-Class is also available in its home market with a less powerful plug-in hybrid powertrain (the 402-hp S450e) and with a 3.0-liter, mild-hybrid, inline-six turbodiesel in two states of tune.

In the S350d, the powertrain makes 308 hp and 479 lb-ft, with the 48V mild-hybrid system adding an extra 23 hp under full throttle. In the S450d, power has been increased to 362 hp, and torque to 553 lb-ft, with an extra 23 hp again available on demand under full acceleration. For context, the S450d's powertrain has 44 percent more torque than the S500's, seven percent more than the S580's, and exactly the same amount as the S580e's hybrid setup. And it's the torque makes the S450d the pick of the S-Class lineup, says Hubert Schneider.

"The torque allows you to accelerate very smoothly from very low speeds," he says, "and it gives you very good fuel economy. At constant speeds on the highway, you can get 39 mpg, no problem, and that means a cruising range of more than 700 miles."

Sure enough, I had been impressed by the smooth and powerful torque delivery on my drive down to St. Moritz. No, the S450d isn't as quick as the S500 from a standing start; Mercedes-Benz's own figures put the diesel S-Class three-tenths of a second slower to 60 mph than its gas-powered sibling, stopping the clock at 4.8 seconds. But once you're rolling, the nine-speed automatic transmission just surfs a tidal wave of torque.

At 100 mph on the autobahn the S450d's inline six was spinning at just 1,750 rpm. On the twisting climb into St. Moritz, before the snow closed in, I switched to Sport+ mode (the quicker throttle and transmission responses are the same as in Sport mode, but it stiffens the air suspension slightly more and drops the car slightly lower to the tarmac) and just left the nine-speed auto to its own devices. Not once did the big Benz feel wrong-footed by the terrain, surging out of tight turns and up steep inclines as the computer adroitly shuffled through the transmission's ratios to ensure the diesel six was kept spinning between 2,000 rpm and 4,000 rpm.

A couple of days later, on dry autobahns heading back to Stuttgart, the velvety muscle in that 2,000 rpm rev band would get the S450d to its 149 mph winter-tire speed limit with insouciant ease. The assertiveness with which the big Benz would accelerate from 80 mph to 120 mph made it easy to hustle along in the fast lane. I could wait patiently for slower traffic to move aside before getting back on the throttle and rapidly resuming our imperious progress back to the hometown of the three-pointed star at triple digit speeds.

Through it all, the trip computer readout reinforced Herr Schneider's point about fuel economy. On the run down to St Moritz it showed the S450d had averaged 28 mpg. The big Benz had used a fraction over a quarter of a tank of diesel for the 230 miles, and the trip computer predicted it would travel a further 375 miles before refueling was required. On the way back, the readout was 27 mpg. That's impressive for an all-wheel-drive luxury sedan weighing nearly 5,000 pounds, with the climate control on and driven as quickly as weather conditions, speed limits, and traffic would allow.

Given my long personal experience with diesel Benzes—my 2021 E220d wagon regularly returns 43 mpg cruising at a constant 75-80 mph, while the 2018 C250d wagon I owned before that would get 50 mpg—I have no reason to doubt the S450d would indeed get 39 mpg under similar conditions. By way of comparison, the six-cylinder S500 is EPA rated at 28 mpg highway, 20 mpg city, and 23 mpg combined.

Quiet and comfortable and packed full of cutting-edge technologies, including the availability of the world's first officially approved Level 3 autonomous drive system, the Mercedes-Benz S-Class is still the blue-chip buy in the luxury limousine segment. In the U.S. last year, the S-Class outsold BMW's 7 Series by nearly two-to-one, and Audi's A8 by six-to-one.

Though, on German pricing, the S450d is more than seven percent cheaper than the S500 and costs 10 percent less than the S580e, there are entirely logical reasons why a diesel-powered S-Class isn't available in the U.S. America's long disdain for diesel-powered cars has been exacerbated by the recent cheating scandals involving diesel emissions testing. Diesels, no matter how efficient, are simply a non-starter here. But after more than 450 miles in the Mercedes-Benz S450d, it's hard to shake the feeling we're missing out on the best all-rounder in the S-Class lineup.