Plug-in hybrids are gaining popularity, offering buyers that don't like the idea of relying on the limited range of a fully electric car (not to mention the recharging network) a chance to start down the route of electrification. Most plug-in hybrid electric vehicles (PHEVs) mate a petrol engine with the electric side of the equation, but Mercedes reckons there's merit in using an economical diesel engine instead, allowing zero emissions running on one side and yet genuine long-distance frugality on the other. Interesting idea. We test drive the new Mercedes GLE 350 de Coupe to find out if it works.

In the metal

At the international media launch of the GLE Coupe, the 350 de hybrid version did without the razzamatazz of the AMG Line specification and, to be honest, we didn't like the look of it, especially in white, where its black plastic arches have nowhere to hide. It looks better in dark colours, but even so, the smaller wheels do the shape of the GLE Coupe no favours. In fact, the regular GLE SUV looks better, and costs less. Thankfully, buyers can pair the far more attractive AMG Line trim with the PHEV powertrain. Not that there's much to let people know you're driving the hybrid model, as the charge port is behind a normal looking fuel flap, on the opposite side to that into which you pour diesel.

The interior of the hybrid model is almost unchanged, too. There are a few unique menu items in the excellent MBUX infotainment system, of course, though the seating is unchanged. That means loads of space for five on board. The boot is a little smaller, but not by much. Apparently, the rear end of the car, and the rear axle, had to be completely redesigned to accommodate the big battery underneath.

Driving it

That battery pack, a lithium-ion unit, has a 31.2kWh capacity. It powers up a highly integrated electric motor in the transmission for up to 100 kilometres (according to the admittedly outdated NEDC regime). That motor is rated at 100kW (136hp) and can propel the GLE Coupe up to 160km/h when you're in the right mode (and country...). In that guise, it's a very smooth and relaxing car to drive and there's plenty of go for urban driving. Our test car also featured the optional air suspension, which turns the GLE Coupe into a seriously comfortable vehicle.

It's less successful on the open road. Even set in its sportiest mode (the air suspension comes with adaptive damping), we found this particular GLE Coupe to wallow through corners and never feel as precise as we'd have liked. No doubt the winter tyres of high profile contributed to this, but it really didn't feel as well tied down as you'd hope such a car would.

At the same time, using the diesel part of the hybrid equation revealed that, while this powertrain can theoretically be very efficient, it isn't very cultured or refined. That 2.0-litre turbodiesel engine is economical and has plenty of torque (especially when operating in conjunction with the electric motor), but it's also really loud when you're working it hard, which detracts from the driving experience no end.

What you get for your money

While we know that the GLE Coupe will be some 10-15 per cent more than the equivalent GLE SUV, we still can't give the 350 de hybrid a rating, as we don't yet have a price for that model as a regular GLE. It's a key bit of information, as well, as, if the PHEV is usefully cheaper than, say, the GLE 350 d, it might warrant a higher overall rating in the grand scheme of things. We will update this test drive once we have the information.

Summary

There's no doubt that the GLE 350 de has the potential to offer its owners really low running costs, especially if they charge up the battery regularly. And yet, they won't be penalised on longer trips, thanks to the inherent efficiency of the four-cylinder diesel engine. Nonetheless, it's not as refined a package as others in the range. That would have less importance, of course, if Mercedes Ireland manages to price the hybrid competitively. And it'll be massively useful for a future that is likely to include zero emissions urban zones...