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Mercedes has introduced a super-efficient diesel-electric plug-in hybrid powertrain to the E-Class. Is it any good?

Our Verdict

Mercedes-Benz E-Class

The Mercedes-Benz E-Class comes with fine engines and a typically laid-back dynamic character. Not one for the interested driver, but a good advert for being disinterested.

2 May 2019

What is it?

Here is a potential solution to the biggest problem with pretty much every plug-in hybrid (PHEV) on sale today.

You see, PHEVs represent for many a great stepping stone to the seemingly inevitable fully electric future of motoring. They’re also a boon to company car drivers, thanks to the significant reduction in benefit-in-kind tax rates they bring.

That’s great, of course, but many businesses that have replaced diesels with PHEVs have actually seen their fuel bills rise, due to users racking up high mileages, where the economy benefit lessens, or simply never bothering to charge them.

While education is a key factor to improving this, it also exposes the main issue with most of today’s PHEVs: once the small electric-only range is gone, you’re left with a heavy car powered by a relatively inefficient petrol engine. Drive a Mitsubishi Outlander PHEV down a motorway on an empty battery and even 30mpg is a bit of an ask at times. 

Mercedes-Benz is aiming to solve that problem with the E300de: a diesel-electric plug-in hybrid E-Class. It’s an almost unique prospect, not just in its segment but across the whole market. VolvoPeugeot and Audi all recently sold diesel hybrids in the UK, but those didn’t exactly fly out of showrooms and have all gone off sale since.

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What's it like?

The E300de is good enough to make us reconsider the whole diesel PHEV format, which conveniently disappeared just as the public attitudes towards the fuel started to change. 

Under the bonnet is the familiar 'OM654' 191bhp 2.0-litre four-cylinder diesel engine that does thoroughly decent service in the E220d. It's mated to an electric motor offering up 120bhp and, more importantly, 325lb ft of torque. The combined system output is a healthy 302bhp and 516lb ft - 14bhp less than the petrol-hybrid E300e but with the same torque output.

This powertrain resolves one of the big stigmas of oil-burners: its healthy 34-mile electric-only range from a 13.5kWh lithium ion battery means any concern over pollutants in cities are quashed. That range is obtained from a 1.25-hour charge from a 7.2kWh charger or five hours via a three-pin household plug.

Bring it into life - silently, of course - and it defaults to Comfort and Hybrid modes. This is a happy medium for the most part, as the powertrain will opt for electric power as much as it can. Measure your throttle inputs (i.e. don’t just clog it everywhere) and it allows a decent turn of pace in electric mode – easily enough to get up to motorway speeds without struggle. 

With a healthy level of charge in the battery, you’ll usher in the engine only up really steep gradients or under full throttle. Doing so exposes perhaps the biggest flaw with the diesel-electric set-up: refinement. This is one of the less intrusive four-pot diesels in its class, but against the silky near-silence of electric mode, its presence at lower speeds is noticeable enough to have you back off to try and convince the system to shut it down again.

There’s also another flaw with the powertrain in Comfort driving mode. Decide you need a burst of power to pull smartly out of a junction and it sometimes dithers for a split-second, seemingly unable to decide whether to switch on the engine or not before firing away. 

Nevertheless, once above 50mph, where executive cruisers like this are most at home, the transition between diesel and electric power is relatively seamless. When the engine does kick into life, it balances driving the wheels and releasing charge into the battery. 

The result is impressive real-world efficiency: a 110-mile round trip on mixed motorway and A-roads with a full charge at each stop yielded nearly 130mpg, with the electric motor managing to match its official range. But the figures impress even when you’ve run the battery down; more than 50mpg is easily achieveable if you’re the type to buy a plug-in hybrid and never plug it in. 

If response is key, Sport and Sport+ driving modes ensure the engine is always on, balancing the two power sources to deliver strong, effortless performance at all speeds. It’s particularly efficient from a standing start, with the electric motor delivering instant torque before the engine spools up to its peak. It lacks the smoothness of a six-cylinder diesel, but given the efficiency benefits, it's an acceptable trade-off.

As usual, you have the option to hold the E300de in electric mode, rely on diesel power and save the battery at a later date or sacrifice some efficiency to charge up the battery via combustion and brake regeneration. The latter system also has a neat feature: even in our SE model without adaptive cruise control, it uses the distance sensor to apply regenerative force when the car in front begins to slow. The subtlety with which it does this makes it far less annoying than it sounds.

Compromises? Well, the E-Class’s platform isn’t as easy to adapt to hybrid propulsion as newer rivals from Audi and BMW, and that shows in the substantial 360kg weight increase over the equivalent E220d. It makes what was never the class’s most dynamic steer that bit more ponderous and less controlled.

The bulk has also had an effect on the ride. It’s still very comfortable and extremely adept at mile-munching, but a little of the regular E-Class’s lovely suppleness has been lost, presumably because the suspension has been firmed up a touch to compensate for the weight. The lack of adaptive dampers or all-round air suspension on our car didn't help matters; both are options you’ll want to consider fitting. What's more, the brakes can be difficult to modulate, due to a numb-feeling pedal, as is common with regenerative systems.

As we’ve become used to with PHEVs, there’s also a practicality sacrifice. The boot drops 140 litres from the regular saloon's to 400 litres, with an awkward cut-out rising from the floor. Happily, unlike the E300e, the E300de is available in estate form to combat this. 

Should I buy one?

Whether or not you should consider the E300de depends on your situation. Those after an executive car solely to beat London’s Congestion Charge and Ultra Low Emission Zone fee might be better served with the more refined and fractionally cheaper E300e or, better yet, the BMW 530e. If you're not doing the miles, you might struggle to recoup the initial outlay.

But there’s plenty to like about E300de’s set-up, particularly for those who combine shorter commutes with motorway jaunts on a more regular basis. It’s one of the only PHEVs on sale that manages to still be efficient once its battery is depleted, which should be a real draw for higher-mileage private and fleet buyers alike.

There are downsides, of course. Refinement and dynamic ability suffer to a degree, although not to the point where the car becomes difficult to recommend. It’s not cheap, either, but then it’s very much on a par with PHEVs of similar size, prestige and performance in that regard.

Pretty much nothing else short of a pricier, less versatile electric car is capable of combining performance, long-legged ability and fuel efficiency in such a convincing package. 

Mercedes-Benz E300de EQ Power SE specification

Where Berkshire, UK Price £47,700 On sale Now Engine 1950cc, 4cyls, turbo, diesel, plus electric motor Power 302bhp at 3800rpm Torque 516lb ft at 1200-2800rpm Gearbox 9-speed automatic Kerb weight 2060kg Top speed 155mph 0-62mph 5.9sec Fuel economy 201.8mpg (WLTP) CO2 tbc (WLTP) Rivals BMW 530e, Volvo S90 T8

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Comments
30

2 May 2019

I have an Outlander PHEV - even with an empty battery and on chunky A/T tyres it will easily average34-35mpg on a long motorway trip.

2 May 2019
Clarkey wrote:

I have an Outlander PHEV - even with an empty battery and on chunky A/T tyres it will easily average34-35mpg on a long motorway trip.

And how are you measuring that ? Proper brim to brim neasurements or using the car's computer ?

XXXX just went POP.

2 May 2019

Brim to brim.  The vast majority of trips are local and done entirely on battery.  Having something that can be effectively electric for weeks at a time but then take off on a trip of hundreds of miles with a quick fill-up is rather good in my experience. 

2 May 2019

£48k for a 2.0 4 pot diesel!. What you need to know is how much a battery, electric motor etc add to the total cost and if it's £8k then how long before it pays for itself let alone save you money. This is something a journalist, any journalist should write.   

"a 110-mile round trip on mixed motorway and A-roads with a full charge at each stop yielded ..,"  Fine if there's a public charger available and you can afford to wait for several hours,  is the electric charge included in that figure.

"more than 50mpg is easily achieveable if you’re the type to buy a plug-in hybrid and never plug it in. " I'd expect near to that from a 2.0 diesel when cruising anyway.

Just sounds like a tax dodge to me

typos1 - Just can’t respect opinion

2 May 2019

On the first point: How much you save/don't save depends entirely on an individual's commuting situation. We'd need to live with one for more than a few days to get definitive numbers. Making a point of it being £9k or so more expensive than an E220d isn't strictly appropriate as you're not just paying for the economy gains, you're also paying for significantly improved performance. And it is significant. 

Second point: I'm fortunately able to charge from a domestic socket at home and at work, if needs be. While this won't be the case for everyone, it's safe to assume that those in the financial position to be able to buy or lease one of these would have at least one of those two facilities. If you do have to use a public charger, you can charge it fully in 90 minutes.

Third point: 50mpg in mixed driving is a good 20% better than an E220d in our experience. 60mpg at a cruise is entirely within reach from out experience. 

Thanks,

Lawrence

 

 

2 May 2019

First point, with the E220d it's not just the £9k or whatever saved on the purchase price you get a smoother car that handles better, brakes better, is more refinement and has better dynamic ability, has a bigger boot, keeps a  spare wheel opt?, steers better, has a better ride..... I could go on and in a £40k+ luxury car these are important.

In the real world it isn't that much faster than a E220d especially if the battery is flat. And with all the handling issues why would you want it that quick? 

I'd be surprized if it gained 20% mpg on a motorway, it's the same basic engine but hauling 360kg of extra weight with little ability to recharge it's battery.

At the end of the day it's about tax breaks and 15% saving in fuel costs, once the tax breaks get reduced it'll cost more at worst or just about pay for itself. Either way you'll end up with a less refined car for similar money.

typos1 - Just can’t respect opinion

2 May 2019

I too have an Outlander and drive to Spain in it two or three times a year. On French autoroutes, with the cruise control at a true 120kph, it cosistently returns 33mpg. Even at the maxium of 130kph it never drops below 31mpg. And this is the old model - not the new Atkinson cycle version.

2 May 2019
Howard Ward wrote:

I too have an Outlander and drive to Spain in it two or three times a year. On French autoroutes, with the cruise control at a true 120kph, it cosistently returns 33mpg. Even at the maxium of 130kph it never drops below 31mpg. And this is the old model - not the new Atkinson cycle version.

And how are you measuring that ? Proper brim to brim neasurements or using the car's computer ?

XXXX just went POP.

2 May 2019

Brim to brim and over several fills. The small (45l) tannk on the Outlander means that I have to stop at least twice each day. The figures I've quoted are in virtually still air. A headwind can increase consumption by >10% and in those circumstances I tend to reduce speed so as to avoid an extra stop. In my experience mpg computers are rarely accurate.

2 May 2019

These hybrid things are obviously tax driven, and as such rather predictably create the opposite result to that intended.

 

I would love to know the percentage of hybrid vehicles on the road at this very minute that have flat batteries, and are therefore producing more emmissions than they would without having to drag around the hybrid clobber.

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