The plug-in diesel-electric hybrid Mercedes-Benz E 300 de delivers up to 30 miles of electric driving range for local journeys, and its diesel engine has the potential to deliver decent economy on long journeys.
There are lots of petrol-electric plug-in hybrids, and even more coming to market, but the Mercedes-Benz E 300 de is only the third diesel-electric plug-in hybrid (after the Volvo V60 and the Audi Q7). In theory, with its new, larger battery than the previous generation E-Class plug-in hybrid model, the E 300 de can deliver zero emission driving locally for up to 30 miles, with diesel economy on long journeys – so how does all this work in practice?
The Mercedes-Benz E 300 de has a 4-cylinder, 2.0-litre diesel engine with an output of 194 hp, a 9G-TRONIC plus nine-speed automatic transmission driving through the rear wheels, together with a 13.5 kWh battery and an electric motor capable of producing 122 hp. The combined system power is 306 hp.
The torque figures make even more interesting reading: the torque of the engine is 400 Nm, and the torque of the electric motor is 440 Nm, giving combined system torque of 700 Nm.
The E 300 de looks like a regular Mercedes on the outside and on the inside (ie. lots of shiny things on the dashboard), but in the boot department the batteries eat into the normal E-Class amount of space, leaving a luggage capacity of just 400 litres. The E 300 de does have a useful braked towing capacity of 2,100 kg.
If you like the Mercedes E-Class then you’ll like the diesel plug-in hybrid, because it’s pretty much identical. That means that the dashboard has a high-tech feel, but one issue is that the steering wheel is offset. Other than that, the seat goes quite low and you can get a decent driving position.
There are four modes of operation: Hybrid, E-Mode (electric only), E-Save (engine only, battery status is retained) and Charge (engine only, battery is charged). It’s important to be aware that these drive modes exist, because when you sit in the car, you can’t see the button which controls these modes, as it’s completely hidden behind the infomedia controller. There are also different drive modes: Eco, Comfort, Sport, Sport Plus and Individual.
For a car in this class, the driven wheels are in the right place – ie. at the rear. And being a Mercedes, you’d hope that the ride is comfortable – which it is. So life on motorways is generally good, although there can be a lot of noise from the tyres on certain surfaces.
If you venture onto country roads expecting performance and agile rear-wheel drive handling, then you’ll be disappointed. This E-Class weighs 2,060 kg, and it feels this heavy. There are steering-wheel mounted paddles to change gear, which are useful, as you often have to change down a lot of gears to get a response; the diesel engine appears to exhibit little flexibility or responsiveness. It can also be somewhat vocal, especially in Sport mode.
If you’re also expecting the instant torque that’s a feature of virtually every other electric car, then you’ll also be disappointed. The electric drive goes through the 9-speed automatic gearbox, so the responses that should be instant are blunted by the slowness of the transmission – and it means that the normally smooth progress of an electric car is instead replaced by an electric car that changes gear. Maybe there’s a place for this sensation in a sports car, but it’s not what you’d expect in an executive saloon.
The dashboard features one wide screen that stretches from the central infomedia screen to the dials in front of the driver. This is high definition, and has a lot of information, and there are many controls that allow you to configure the information to your preferences. In our opinion, there’s too much information, and the controls for the system aren’t that intuitive – lots of controls for the satnav in particular are hidden away.
On a similar note, the self-steer and lane assist buttons are completely hidden from view by the steering wheel. And again in traditional Mercedes fashion, the parking brake is a button at the bottom of the dashboard to the right-hand side of the steering wheel.
If you were to drive a Tesla Model 3 and then this E-Class – as we did – then you’ll be very aware of the massive contrast between having absolutely no buttons in the interior of the Tesla, and a dashboard full of buttons and controls in the Mercedes.
The official WLTP combined fuel economy for the Mercedes-Benz E 300 de is an impressive-sounding 201.8–176.6mpg, with CO2 emissions of 41 g/km. The official electric driving range is around 30 miles; we averaged 25 miles in real-world driving.
On long motorway journeys we averaged 55.4mpg at 70mph, and 80.7mpg at a constant 50mph. Although the 25-30 mile electric range is ideal for local journeys, this capability is also useful to supplement the diesel engine at low loads on motorways, when it can help to deliver impressive economy. On A and B-roads we averaged 48.7mpg. Overall after a week with the car we averaged 54.3mpg, which is respectable for a two-tonne executive saloon. However what is perhaps most impressive is the driving range: a predicted range of 672 miles was displayed (a 66 litre diesel tank helps with this).
The on-board charger capacity is now 7.2 kW and the E 300 de can be charged from a 7.2kW charger in one and a quarter hours, or from a standard UK three-pin socket in around five hours. The charging port is in a slightly unusual position in the rear bumper.
The Mercedes-Benz E 300 de AMG Line Saloon costs £50,195. However our test car had the options of Obsidian black metallic paint (£685), Premium Plus package (£4,395), Comfort package (£3,295) and Driving Assistance Plus package (£1,695), Night package (£595), taking the total price as tested to £60,860.
Thanks to its low emissions, the E 300 de has a low company car tax benefit in kind rating of just 16%, potentially saving drivers thousands of pounds per year.
There’s also a diesel-electric plug-in hybrid E-Class estate – which would get our vote over the saloon for being more practical – as well as a petrol-electric plug-in hybrid saloon.
Most plug-in hybrids have a petrol engine. That means that in real-world driving they’re often not very economical on long journeys. In the current ‘anti-diesel’ climate, Mercedes is being brave offering a diesel-electric plug-in hybrid, but it’s a welcome choice for people who drive up to 25-30 miles locally, which can be done on zero tailpipe emission electric power, and who also drive long motorway distances. Our average fuel economy figure for the week of 54.3 mpg – based on our normal driving mix of 80% long journeys – shows that the Mercedes-Benz E 300 de AMG Line Saloon can be reasonably economical for a large executive saloon.
On the downside, the electric drive going through the gearbox means that the normal instant electric torque is impacted by the slow responses of the transmission, and the functionality of various aspects of the interior could be improved.
Overall the Mercedes-Benz E 300 de AMG Line Saloon gains a Green Car Guide rating of 8 out of 10. Our next job is to review the all-electric Merc EQC, which has ditched an internal combustion completely, to see how that compares. Watch this space.