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Third-generation four-door coupé is the first to get hybridised AMG powertrain

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Is the world ready for a grand touring performance saloon, powered by a hybrid powertrain and from Mercedes-AMG?

Perhaps it would be better to ask if there is another performance car maker whose emergence has depended more squarely on the raw, unreconstructed allure of the V8? It’s doubtable. Ten years ago, the idea would have been laughable. Plenty might still laugh at it today.

If Mercedes UK decided to import the 53 version of the AMG GT 4-Door to the UK, I’m sure it would sell. But I’m not sure I could find 25,000 good reasons — or whatever the price difference might be — to buy it over this car.

And yet it’s happening. Mercedes’ in-house performance marque, right now in 2018, is in the final stages of preparing to launch a ‘halo’ hybrid hypercar with more than 1000bhp while already filtering a new breed of petrol-electric options into several strata of its showroom range that’s probably even more relevant and interesting to the majority of AMG owners than its incredible range-topping One will be.

Affalterbach’s first petrol-electric powertrain has, in fact, been squeezed snugly under the bonnet of this week’s road test contestant: the ‘C257’, third-generation Mercedes CLS, here to bid for your interest in new and intriguing ‘AMG 53’ suffixed form. So now we find out if Mercedes’ hybrid technology is mature enough to stand up to the kind of examination through which the Autocar road test team expects to put a proper super-saloon.

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The CLS isn’t the only Mercedes-AMG model into which this hybrid powertrain – consisting of a 3.0-litre straight six with an intriguing system of forced induction and an electric motor hooked up to it – is being squeezed. There’s an Mercedes-AMG E 53 coupé and convertible, too, with most of the same vital statistics on power, performance, economy and emissions – although, for the moment, no other 53 models.

Mercedes-AMG is sticking broadly to the strategy of offering a hybrid 53 model on derivatives of its longitudinally engined cars where it doesn’t offer a 43 and 63; which means we shouldn’t expect one on any of its traditional saloons, at least for the time being.

What Car? New car buyer marketplace


Mercedes-AMG CLS 53 2018 road test review - hero rear

The headline here is that no longer does a thunderous eight-cylinder 63 derivative of the CLS exist. Those who crave a four-door coupé armed with such an engine will now be directed to the new four-door version of the AMG GT, while the CLS range climaxes with the straight-six 53 tested here.

Displacing just under three litres, AMG’s new 53 powerplant uses a single yet substantial conventional twin-scroll turbocharger, but it compensates for the inevitable latency of such a turbo with a smaller secondary, electrically powered ‘compressor’ mounted adjacent to the inlet ports. What results, on paper, looks like a quite spectacular spread of torque, with 384lb ft available between 1800rpm and 5800rpm, and peak power arriving reassuringly far around the tachometer, at 6100rpm.

While far from unattractive, this latest CLS has lost the visual wow factor of the original 2004 model. A four-door coupé isn’t as radical an idea now as it was then, but this execution isn’t overwhelmingly pretty

And yet on top of that comes an extra layer of motive power supplied by an electric motor that also serves as starter-alternator for the car. Mounted between the engine and nine-speed automatic gearbox, it’s fed by a 48V system and an enlarged battery. And, as well as allowing the car to save fuel by coasting ‘engine off’ for prolonged periods and supplying the current necessary to drive that electric blower, the 48V system and drive motor combine to supplement the engine’s 429bhp and 384lb ft with up to 22bhp and 184lb ft (although, because it does most of its assisting at low crank speeds, you shouldn’t simply add two and two together and conclude this is a 568lb ft powertrain).

The car’s bodywork – less distinctive than earlier CLS generations but in no danger of being mistaken for an Mercedes-Benz E-Class saloon – rests on firmer, AMG Ride Control+ air springs with adaptive dampers, and has multi-link suspension front and rear. It’s a self-levelling set-up that lowers at speed but can be manually raised for steep driveways and the like. There are three pre-sets for the suspension ranging from Comfort to Sport+, and two that alter the assistance of the electromechanical steering. Along with similar pre-sets for the engine, driveline and transmission, it should be possible to tailor the CLS 53 to any road you care to point it down.

The car has 4Matic+ four-wheel drive as standard, the torque split between the front and a permanently driven rear axle varying continuously in line with conditions under-wheel. It’s not calibrated purely with entertainment in mind, though – and, unlike with its four-wheel-driven 63 S models, AMG doesn’t include a rear-drive-only Drift mode here.


Mercedes-AMG CLS 53 2018 road test review - cabin

The CLS 53’s isn’t a classic super saloon cabin, but instead pretty plainly one of a very modern, very advanced and seriously luxurious four-door GT subtly tweaked for a bit of go-faster flavour.

The car’s heated and ventilated massager seats don’t look like they’re about to hold you in place during the best drive you’ve had in ages, but it wouldn’t be beyond them. They have discreet AMG badges, as does the car’s steering wheel and its sill plates.

‘open-pore ash wood’ trim doesn’t look as natural as its billing suggests. Only Edition 1 models avoid it, in favour of lacquered carbonfibre.

But, with the notable exception of an AMG-specific digital instrument display mode that you may or may not discover, those badges are actually the only discernible signs that the car has been through any kind of performance makeover at all.

One of the advantages of opting for the CLS 53 is that it gets as standard the Premium Plus package that’s a near-£4000 extra on any other Mercedes-Benz CLS. It means a 13-speaker Burmester stereo, 360deg parking cameras and Mercedes’ Comand Online infotainment system in all its glory.

The car has a pair of 12.3in-wide screens, placed side by side to look almost like one continuous display. The central display isn’t touch-operable but you can get to grips with it by using the rotary ‘scroll-wheel’ device on the transmission tunnel, the fingertip input pad above it or the thumbpad input on the steering wheel. Most road testers preferred the thumbpad, mainly because using it doesn’t require you to take a hand off the wheel.

The system doesn’t feature the A-Class’s latest ‘Hey Mercedes’ voice recognition software, but it accepts voice commands for navigation destination inputs and the like at the first time of asking.

The Burmester audio system is excellent and impressively resistant to distortion at high volumes.

The mix of cabin materials looks ritzy and expensive, the overwhelming majority of them substantial and pleasing to the touch. Its side-by-side windscreen duo of instrumentation and ‘infotainment’ displays broadcasts the car’s technological sophistication in what may seem, at first, an almost confrontational way. You get used to that quickly enough and it ends up being anything but distracting. Still, what you’re getting in the interior of a CLS 53 is, by and large, what you might get inside any other CLS, equipment level notwithstanding: material richness, tactile quality and plenty of what the Germans like to call ‘technical fascination’.

As far as practicality goes, the CLS holds an advantage over some of its rivals by offering belts and seats for three across the back row – although, as an adult or even a teenager, you wouldn’t want to occupy the car’s fifth seat for long. In the outer back seats, there’s space for all but the tallest adults to get comfy, with an entry and exit routine made slightly awkward by the car’s curvy profile.

Boot space is decent, though not as generous as it is in an Audi A7 Sportback or a Porsche Panamera; and not as accessible either because the CLS still has a bootlid while its German rivals both have hatchback rear ends. Here, you do feel that a trick is being missed; and it probably wouldn’t be if Mercedes hadn’t cancelled the CLS Shooting Brake replacement after the four-door had been designed.


Mercedes-AMG CLS 53 2018 road test review - engine

Despite being two cylinders down compared with its 63-badged brethren, the CLS 53 still conjures some of the aural thrills (albeit slightly synthetic ones) you’d expect from one of Affalterbach’s more menacing creations.

While not as earth-shatteringly raucous as those V8-powered models, the 53’s inline-six is a characterful unit, being silky-smooth in timbre at low speeds, while an extended prod of the throttle will be met by a crisp, mellifluous growl that gets more dramatic as you approach the 6500rpm limiter.

The V8, 549bhp CLS 63 S we tested in 2011 was just 0.1sec quicker from 30-70mph - a metric that perhaps gauges usable accelerative potency better than any other

Volume-wise, the CLS was measured at 78dB at max revs in fourth gear – 2dB quieter than the V8-engined GLC 63 S Coupé we tested in June. Off the line, the CLS doesn’t suffer from any noticeable shortage of traction or hesitancy from the nine-speed ’box. It recorded a two-way average 0-60mph time of 4.3sec, which is well in line with Mercedes’ 0-62mph claim of 4.5sec.

The manner in which acceleration is delivered is impressively linear, and there’s little turbo lag evident at any point in the rev range. Lock the CLS in its most aggressive Sport+ driving mode and upshifts are executed with just enough ferocity to remind you that, despite its lack of V8 engine, the 53 is a potent straight-line machine.

That potency is evident when it comes to the CLS’s overtaking ability, too, with the 30-70mph sprint being dispatched in 3.7sec. The last-generation CLS 63 S we tested back in 2011 (5.5-litre V8, 549bhp, 590lb ft) bettered that time by only one-tenth of a second. The earlier car was superior in terms of flexibility; locked in fourth gear, the 63 S would accelerate from 30-70mph in 5.6sec, while the new 53 takes 6.1sec.

Still, this is evidence that, while it might not have the laid-back, any-condition pace of an AMG V8, the CLS 53 will hit a comparable outright performance level if you’re prepared to really put its six-pot to work.

Of course, without that whopping V8 under the bonnet, the CLS 53 doesn’t quite have the propensity to drink fuel at the rate its predecessor did. It returned a brim-to-brim touring test economy result of 39.2mpg, while the 63 S could only manage 25.8mpg.


Mercedes-AMG CLS 53 2018 road test review - cornering

The manner in which the CLS 53 rides is arguably the least AMG-like aspect of its on-road demeanour.

Where the full-fat 63-badged models – even those that ride on air springs – make notable sacrifices of rolling comfort in the name of connectedness with the road surface, the CLS comes across as a relative softy.

Compression after sweeping turns brings no response from the ESC, allowing you to charge out on exit without being hampered by a lack of power

On threadbare British roads, there’s far less of the sharp-edged jostle and thump that’s typical of the low-speed ride of a modern 63, with the CLS 53 being more open to the idea of at least attempting to smooth over the occasional lump or bump.

That’s not to say its secondary ride is seamless: there is still a degree of bristling resistance to inputs here even with the car’s dampers set to their softest, though by no means enough to dissuade you from the idea of daily-driving the CLS.

Adding some pace is the key to really making the CLS shine. The balance between vertical body travel and ride comfort has been well struck, with the air-sprung Mercedes remaining impressively composed over undulating surfaces, while still maintaining that sense of pliancy you’d expect from a luxury four-door coupé, even an AMG-badged one. And the pay-off is that the CLS 53 makes for a compelling long-distance tourer: one that could make otherwise arduous motorway miles not just bearable but really enjoyable – something you can’t say about all of Affalterbach’s models.

Reasonably quick steering – we measured 2.4 turns lock to lock – lends the CLS a front end that’s by no means averse to turning in, but the electromechanical rack doesn’t quite offer the incisiveness or feel you get from the likes of the Porsche Panamera.

It’s also difficult to shake the sense that a degree of its potential handling finesse has been sacrificed in the pursuit of those heightened comfort levels. Roll around its longitudinal axis is still neatly contained and controlled given the car’s size and heft, mind, and there’s abundant grip. But, when push comes to shove, either on a truly testing road or on a track, this isn’t quite the thrill-a-minute driving machine you might have hoped for – or that bigger-engined AMG saloons prove themselves to be so regularly.

The relatively soft suspension of the CLS 53 does have a marginally adverse effect on the precision and composure with which it tackles Millbrook’s Hill Route. Numerous high-speed directional changes serve to emphasise the car’s mass and hamper, to an extent, its sense of mid-corner adjustability. Corners over crests can cause the Mercedes to skip about on the road surface, too, although never in an alarming or dangerous fashion.

Mercedes seems to have a knack for crafting well-calibrated electronic stability control systems, and that holds true for the CLS 53. This is particularly highlighted by the conservative approach it takes when stepping in early but with subtlety through the Hill Route’s numerous compressions, where sudden downwards travel can often result in a heavy-handed response from less-sophisticated systems.


Mercedes-AMG CLS 53 2018 road test review - hero front

With the demise of BMW’s 6 Series Gran Coupé and the absence of a medium-rare Audi A7 Sportback, there’s only one true rival for this CLS 53.

Porsche’s venerable Porsche Panamera is our current class leader, and there are several reasons why keen drivers might shun the Merc in that car’s favour, but price isn’t one of them.

Merc is outgunned by the Porsche in depreciation stakes, while less powerful Audi also performs more favourably

To get comparable performance and four-wheel drive, you’d need to opt for the £90,000 Panamera 4S, and then add £1600 for the air suspension that’s standard on the CLS 53.

The less-powerful Panamera 4 has a lower entry ticket than the CLS and holds its value better, but would you miss that scalpel-sharp turn of pace?

Incidentally, the most recent BMW M5 – the fiendishly quick F90 – can now be found for around £80,000 with little more than delivery miles. It’s slightly unfair to bring lightly ‘pre-owned’ saloons into the equation but, for now, finding rivals for this Mercedes demands some creativity.

If the CLS 53 still gets your nod, you’ll at least have convenience on your side. The 66-litre tank isn’t vast but a touring economy of 39.2mpg makes for a range of 569 miles.

What Car? New car buyer marketplace


Mercedes-AMG CLS 53 2018 road test review - static hero

Some observers may regard this new six-cylinder AMG as an irrelevance; an effort to justify the existence of Mercedes-AMG’s new £135,000 GT63 S 4-Door.

There might be a grain of truth in that, but the assessment would be otherwise unfair, because the CLS 53 has proved itself to be impressive and capable in its own right.

Mould-setting AMG hybrid is well worth its place in the model range

The manner with which it combines its rich and complex powertrain with an opulent interior, smooth ride and sharp handling lends the CLS a distinct and appealing identity.

It’s a different take on what an AMG performance model can be: quick and engaging when you want it to be, comfortable and refined when you don’t. And it’s more enticing than AMG’s last attempt at a feeder line: the turbo V6 43.

Were it not for the existence of the Porsche Panamera S – which pulls off the same trick only with a shade more success – the CLS 53 would have likely claimed a more prominent position in our top ten.

So while it isn’t quite the match of its Swabian rival on outright driver appeal, the CLS is a car you could easily make a case for.

What Car? New car buyer marketplace

Matt Saunders

Matt Saunders Autocar
Title: Road test editor

As Autocar’s chief car tester and reviewer, it’s Matt’s job to ensure the quality, objectivity, relevance and rigour of the entirety of Autocar’s reviews output, as well contributing a great many detailed road tests, group tests and drive reviews himself.

Matt has been an Autocar staffer since the autumn of 2003, and has been lucky enough to work alongside some of the magazine’s best-known writers and contributors over that time. He served as staff writer, features editor, assistant editor and digital editor, before joining the road test desk in 2011.

Since then he’s driven, measured, lap-timed, figured, and reported on cars as varied as the Bugatti Veyron, Rolls-Royce PhantomTesla RoadsterAriel Hipercar, Tata Nano, McLaren SennaRenault Twizy and Toyota Mirai. Among his wider personal highlights of the job have been covering Sebastien Loeb’s record-breaking run at Pikes Peak in 2013; doing 190mph on derestricted German autobahn in a Brabus Rocket; and driving McLaren’s legendary ‘XP5’ F1 prototype. His own car is a trusty Mazda CX-5.

Mercedes-AMG CLS 53 First drives