► CAR lives with a diesel hybrid Mercedes GLC
► It’s unique, but does that make it good?
► We’ll find out over a few months
For a powertrain that seems to make so much sense, it’s perhaps surprising that Mercedes-Benz is the only car maker currently offering a plug-in hybrid diesel. The logic runs that an electric powertrain covers most trips, but the super-frugal four-cylinder diesel steps in once battery charge is depleted.
In the real world of drivers plugging in much less frequently than governments hoped, it could represent a better solution than a petrol plug-in.
We’re welcoming the Mercedes-Benz GLC 300de to the CAR fleet, the plug-in diesel version of Mercedes’ mid-size SUV and rival to the likes of the BMW X3, Volvo XC60 and Audi Q5.
It promises no range anxiety and no need to wait about to charge, and with better mpg than an equivalent petrol plug-in hybrid too. This GLC 300de’s five per cent benefit-in-kind tax rate also compares favourably with an EV’s two per cent rating and falls way below the comparable purely diesel GLC’s 35 per cent. (The plug-in petrol 300e is equally attractive.)
So if you want most of an EV’s tax break but fewer of its drawbacks, the GLC 300de could be a highly tempting sweet spot.
Volvo was first to the plug-in diesel niche with a series-production car in 2012 (the Swedes now don’t do diesel at all), but Mercedes has been producing plug-in diesels since the E-Class PHEV debuted in 2018. The GLC 300de first arrived later in the first-generation’s life cycle in 2020 then returned with the second generation for 2022.
Its fundamentals comprise a 1993cc four-cylinder diesel engine, nine-speed auto and all-wheel drive with a 31.2kWh lithium-ion battery and e-motor good for up to 80 miles’ e-range. The latter represents a big improvement on the last-generation model, with its 13.5kWh battery and tiny 27.3-mile range.
Combined output of 328bhp with 553lb ft is pretty healthy (194bhp and 325lb ft torque from the engine, 134bhp and another 325lb ft from the single electric motor) though the 300de is also the heaviest GLC you can buy – a kerbweight of 2310kg is about 350kg portlier than a regular diesel, and 250kg more than the previous 300de owing to the larger battery.
Pricing starts from £61,100 in Urban Edition trim, then walks up through three different AMG Line variants with a big ta-da! at £75,610. We’re testing the entry-level trim, with only this car’s attractive Spectral Blue metallic paint adding £715 to the RRP (sorry Countach owners, the ’KIN’ LAMBO! plate isn’t mine to sell).
Adaptive LED headlights, a parking package with reversing camera, heated electric door mirrors and moody black exterior trim are all standard. This car also rides on 20-inch multi-spoke alloys with coil springs up front and air suspension for the rear.
More important for my two teenagers are the MBUX multimedia system with its 12.3-inch digital instrument binnacle and 11.9-inch portrait-orientated touchscreen, wireless charging pad and – most crucial of all – multi-colour ambient lighting and huge puddle lights that project the three-pointed star on the ground like a reverse bat signal.
A couple of key reasons are usually cited as to why other car makers don’t do plug-in diesels. One is expense, because a diesel engine is already more expensive to produce than petrol before you start adding hybridisation.
Diesel is also more efficient than petrol, so you’re into diminishing returns with trying to make it more efficient still with plug-in hybrid tech.
Because Mercedes – rather remarkably – also offers a petrol plug-in GLC as well as equivalent four-cylinder petrol and diesels, it’s possible to directly compare all this.
In terms of pricing, the GLC petrol plug-in is £2250 cheaper than our diesel, though that’s true across the line-up for petrols and diesels, not to mention other makers’ model lines. As for efficiency… Well, the official stats do show a bigger gain for the petrol, but the improvements are so extreme they should be taken with a pinch of salt – my calculator says the plug-in diesel’s 565mpg is 1039 per cent more efficient than the 300d’s 49.6mpg, while the plug-in hybrid petrol posts a 1117 per cent increase with 470.8mpg compared to the 300 e’s best of 38.7mpg.
Plug-in hybrids are the most use-case dependent of all powertrains, of course, which makes the official triple-digit WLTP mpg figures even more meaningless than usual. It’s also where this long-term test comes in.
My driving routine is probably representative of the ideal customer, with lots of short- to medium trips achievable on a battery charged from home, then less frequent longer runs to random locations where I don’t want to be hostage to the hassle, uncertainty or much higher prices of public charging points.
It’s going to be fascinating to see how we get on.
Logbook: Mercedes GLC
Price: £61,110 (£61,825 as tested)
Performance: 31.2kWh battery, 1993cc four-cylinder turbodiesel plus e-motor, PHEV, 328bhp, 553lb ft
Efficiency: 565.0mpg (official), 75.6mpg, 4.2 miles per kWh (tested), 11g/km CO2
Energy cost: 14.3p per mile
Miles this month: 877
Total miles: 2427