Mercedes-Benz S500 Plug-in Hybrid 2015 Review

More than 80,000 cars in to the career of the latest S-Class, Benz has found a problem with it. While the traditional three-pointed star's flagship might be more economical than ever before, it's still so heavy that its consumption figures have it upside down on fleet average emissions.

Not that your typical S-Class owner cares. The EU, China and the US governments might, though, which is why the S-Class range now boasts this, the first plug-in hybrid to carry a Mercedes-Benz badge into production. And it's even heavier.

Benz has taken great pains to convince its S-Class-type people that this is a guilt-free, technology-leading alternative to the V8-powered S500 with similar speed and power and equipment and luxury. It has also taken great pains to convince everybody else that it's capable of masquerading as an electric car for 33km before it has to fire up the fossil fryer to go further, delivering a total NEDC combined consumption number of 2.8L/100km.

It's the best of both worlds, according to the Daimler spin, and there's plenty of truth in that yet, as we found on our 170km test in Denmark and Sweden but the big limo isn't without holes in its environmental pretentions.

It's based around the highest level of the S500's equipment package, so that means the three-mode air suspension system is standard, along with seat heating and ventilation, those wickedly indulgent soft headrests and a pair of unmistakeable 12.3-inch rectangular TFT screens front and centre. Not only that, but you can pre heat or pre cool the cabin via your mobile phone.

The headlights are full LED versions, as are the taillights, the best of Benz's climate control air conditioning options, seven different ambient light colours and the plushest seats in the any German car.

There is also Benz's full Comand multi-media system (which had three full system crashes on our test, coming back in English twice and German once), along with enough electronic preventative anti-crash equipment to make you raise a suspicious eyebrow towards anybody who bends one.

Benz tech boffins freely admit the plug-in hybrid is unashamedly targeting its own (non-AMG) flagship, pointing out that its 5.2sec sprint to 100km/h is just 0.4sec shy of the V8's number in spite of being 200kg heavier. And that's more than just talk, because it can swing two motors to bear any time it needs to.

The first of those is a turbocharged, 3.0-litre petrol V6, complete with 245kW and a crunchingly strong 480Nm from only 1600rpm. It's an engine drawn from the standard Benz engine pool, then it's fiddled for more efficiency so it doesn't need to feel guilty when it looks at the smug electric disc motor sitting next to it.

The M276 V6 uses a pair of variable-geometry turbochargers, scores a 200-bar direct fuel-injection system, has a head and block made from aluminium and its ultra-thin cylinder liners have been sprayed on cleverly using the same low-friction Nanoslide technology Benz's F1 team adopted at the start of this season.

There are two camshaft adjusters each to help manage the intake and exhaust valves and the piezo injection nozzles allowed Benz's combustion wizards to deliver several spray-guided injections per bang.

It follows that up with an electronically controlled on-demand oil pump, while all of the engine's ancillaries are also operate on-demand.

The other part to the powertrain equation is the electric motor. If it looks and sounds familiar, it's because it's a modular step-up from the disc-shaped motors Benz has used in other hybrids (even the S400 Hybrid it already has on sale), but it uses nine rotor plate packs instead of the lesser model's six.

Fitted snuggly inside the housing of the seven-speed automatic transmission (whose cooling it piggy backs), the permanently excited synchronous motor contributes 85kW and an instant 340Nm of twist.

Join the two power units together and Benz is talking a total system output of 325kW and 650Nm (no, not 820Nm), so on the surface it's in the S500 V8's ballpark for grunt and it tops out at the same limited 250km/h, too.

The party piece, though, is that the Plug-in Hybrid is a plug-in hybrid --capable of being fast-charged in two hours or slow (10amp household socket) charged in less than four. And then it can be a pure-electric runner.

As our drive showed, it's a useful and swift electric runner, too. If the S-Class is a quiet operator in its standard form, then the silence is astonishing in the Plug-in Hybrid. It's almost unbelievably quiet.

It's more than capable of riding the torque wave to slip in and out of traffic cleanly and, well, as arrogantly as you'd expect of an S-Class. There's a sophistication to the electric powertrain, too, that other cars don't show. There are no wobbles or harmonics from the e-motor, just silent urge.

For some, 33km of electric range will be enough for a day. For others, it isn't so much. We found the S500 Plug-in Hybrid running out of juice on a convoluted run from Copenhagen airport into the city. And Copenhagen isn't that big.

This would have been a much more impressive feat, though, had the Volkswagen Golf GTE not been launched a week earlier. Not that anybody's cross shopping them, but the little Volkswagen has 50 per cent more electric range (50km) and doesn't compromise its luggage space.

The S500 Plug-in Hybrid might still have 395 litres of boot space, but it's an odd shape and you will lose a bit more by accommodating the charging-cable bag. Besides, 395 litres is just 15 litres more than you get in a Golf -- and the hatch's rear seats can fold flat to boost that. The four-seat Benz's rears don't.

The Volkswagen battery pack is in the floor, while the Benz's sits above the rear axle, and while the two cars share the same battery charge capacity, the Volkswagen is about 700kg lighter.

And that raises (foreseen) issue with the S500 Plug-in Hybrid. S-Class buyers. By Benz's own admission, aren't the type of people with the patience to plug the big limo in to a power point when they arrive at the office, unplug and then plug it in again when they get home. Every day, flipping the flap beneath the right tail light...

To solve that problem, Benz (in conjunction with BMW) is working on wireless (inductive) charging, which will mean dropping a plate in the garage that you just park on top of, then walk away. They admits it's somewhere between two and four years from production.

In the meantime, though, the only non-cable charging solution is what Benz's shuttle drivers did overnight with the test cars: drive around in its Charge mode, with the V6 biturbo engine being turned into a generator as well as a standard powerplant. That's fearfully anti-environment, though. With the 2215kg kerb weight giving the V6 enough to do without being loaded up by another 12kW to deliver 30 Amps into the 8.7kW/hr battery pack, it takes nearly an hour of driving to bring the battery up to a full charge.

As we found, the car will switch into this mode automatically when the battery's juice falls below 2km of electric range. When it does, it adds somewhere between 4-6L/100km to the V6's instant consumption figure.

The real clever part about the way the S500 Plug-in Hybrid operates, though, is as much software as hardware. The battery's energy feeds the electric motor via a water-cooled DC/AC converter in the engine bay, while there's also a DC/DC converter feeding up to 3kW of power to drive cabin's 12-Volt systems. The entire thing – all of the electric comings and goings – is controlled by a development of the SLS Electric's power control hardware and software.

And you can feel that ongoing development work in every kilometre you're in the car. Its petrol motor chimes in and out of business so seamlessly that not the barest hint of a shudder comes through the seat or the wheel. It's a quieter motor than it is in most Benzes with the standard version, too, but it's not as smooth as the V8 and it breaks up the silent spell spun by the electric power.

When it's working in concert with the electric motor, it can help bunch the big girl's skirt up nice and high so it can stretch its legs. It is bloody rapid once the cage is rattled and sounds pretty clean and smooth and unruffled doing it.

It's best left in its Hybrid mode, when the brain sorts out what motor should be doing what, when. In Hybrid mode, it repurposes braking energy for the battery, then shoots out little, barely perceptible jabs from the electric motor each time you get back on the throttle out of a corner. It does this, Benz says, because it helps spin the driveline up with torque to get the petrol motor spinning at precisely the right revs again. Call it la-de-dah heel and toe, but going up in speed rather than down.

The system can also decide to coast the car, disconnecting all of its motive power to let the big rig sail along freely until you decide you need to touch a pedal again.

Another feature is that it takes its active cruise control and uses even that to regenerate juice. If you come up to another car that's a bit slower, it will unhook the tools and let the car sail. If you come up on one that's a lot slower, it will brake using the electric motor instead, pumping more juice back into the battery.

The thing just works, too, effortlessly slipping from one mode to the next and not asking the driver to do anything different, unless you want to really maximise the economy (though how many S-Class owners will be bothered with that).

You can barely tell when the electric motor is chiming in and fading out and the highlight really is how imperceptible all of this frantic electronic trickery is to anybody inside the cabin.

Benz's brainiacs suggest the driver will make a difference of about 30 per cent to the fuel consumption figures, but even that doesn't account for our inability to get within a bull's roar of the official NEDC figure.

While we hit the Golf GTE figure right on the nose, a 150km drive in the S500 Plug-in Hybrid that started in the electric mode in Copenhagen and meandered, at the speed limit, through the relatively flat country of Malmo and the Scania region of Sweden gave us 8.0L/100km.

It's the sort of number you might achieve from the S500 V8 if you drove it very carefully and we were frankly disappointed. Turned out nobody else who drove it in a day-to-day manner did any better.

That being the case, you might be better off utilising the E-Save mode to keep a full electric charge and use the petrol motor instead, switching to electric only when you get to the thick of the traffic in your city.

Or you might be better off saving some money and looking at one of the S-Class's diesel variants. Apart from the useful, but limited pure electric mode, the real-world economy won't be much worse.

Mercedes-Benz has committed to bringing 10 plug-in hybrid electric vehicles (PHEVs) to market by 2017, and the S-Class Plug-in Hybrid will be the first of those to arrive Down Under late next year (2015).

The company says pricing will be in line with the 4.7-litre twin-turbo petrol V8-powered S 500 with which it shares its model designation, meaning (based on Sept 2014 pricing) around $285,000.

The first plug-in C-Class will also come to Australia in 2016, priced around $100,000.

2015 Mercedes-Benz S500 Plug In Hybrid pricing and specifications:
Price: TBA (close to S500 V8)
Engine: 3.0-litre, petrol, V6, turbocharged, disc-electric motor
Output total: 325kW/650Nm
Output Petrol: 245kW/480Nm
Output electric: 85kW/340Nm
Transmission: seven-speed automatic
Fuel: 2.8 litres/100km
CO2: 65 grams/km
Safety Rating: TBA

What we liked:
>> Fast when needed
>> Imperceptible engine transitions
>> Sumptuous interior

Not so much:
>> Not always economical
>> S-Class owners and cables? Really?
>> Short electric range