The Mercedes-Benz GLC 300 de 4MATIC adds an unusual diesel plug-in hybrid option. Is it as good as the Audi Q5 and BMW X3 alternatives?

PROS: 

+ Very comfortable over long distances

+ Good standard equipment

+ Interior design and quality

CONS: 

- Battery range is at best average

- Reduction in boot capacity

- Not very engaging to drive 

Verdict: The Mercedes-Benz GLC was already a good premium SUV, but adding a plug-in hybrid powertrain gives it further appeal. The fact that it’s matched to a diesel engine is odd, but there’s some merit to the setup. 

2021 Mercedes-Benz GLC 300 de 4MATIC review: the five-minute read

There isn’t much that separates the players in the premium mid-size SUV market, but the Mercedes-Benz GLC does offer a wide range of different options. These include a rip-snorting 503bhp V8 with the full AMG treatment, but it’s the plug-in hybrid diesel we’re reviewing here. 

The arrival of plug-in hybrid powertrains does add some eco-credentials to the SUV movement, but the decision by Mercedes to also offer a diesel PHEV leaves it as something of an outlier. It uses the same battery setup as its petrol-engined equivalent, but with a diesel engine taking over things when that 13.5kWH battery runs out, it can continue to go further while using less fuel. 

All of the GLC models come with the AMG Line exterior styling that complements the design of the Mercedes. That includes 19-inch wheels, the diamond radiator grille and a sporty body kit and bumpers with metallic inserts. Even though it has been two years since it last got some styling tweaks, the GLC is ageing very well. 

As with several of its other plug-in hybrid models, Mercedes places the charging port for the battery on the rear bumper. That’s convenient with some public charge points but is something to consider depending on how your domestic charger is located. 

Climbing inside reveals a cabin that is a lovely balance between classy premium materials and modern-day tech. Optional trims include open-pore wood make a pleasing visual contrast against the inset metallic air vents and the touchscreen display that appears to float on the centre console. 

Rear passengers are unlikely to have too much to complain about when it comes to space, though fitting in three adults across the rear can be a bit of a squeeze. One of the downsides of that large battery in the back is that boot space is compromised, with the GLC taking a 155-litre hit over its combustion-engined siblings. 

However, having that battery onboard does make driving the GLC with only electric power be quite an enjoyable experience. There is no lack of instant shove from the electric motor. It isn’t as seamless as a fully electric vehicle when moving away from a stop, but it glides along in near-silence. Providing you have sufficient charge can dispatch short motorway journeys thanks to its 87mph top speed in EV mode. 

Once the battery has dispensed its charge, the four-cylinder diesel does a fine job spinning into life with little fuss. It will continue to run this way until the battery regains some charge through energy recuperation when slowing down and braking. From this point on, the GLC acts as a hybrid, sharing the driving load between the two motors as appropriate. 

Having diesel power makes the GLC that bit more efficient over long distances, as it has more torque to haul the added weight of the PHEV system around when it isn’t in use. This element alone gives the GLC up to an additional 30mpg over the petrol-engined plug-in version. 

Better still is that the GLC is a very comfortable car to spend lengthy journeys in, with supportive electrically adjustable seats in the front and enough space for those in the rear to stretch out. There isn’t much noise seeping into the cabin at speed while the ride quality is set up more towards comfort than dynamic driving. 

You can feel the extra weight that the GLC 300 de carries over its pure diesel counterpart when slinging it through faster bends. Thankfully all-wheel drive comes as standard to help it maintain its line well. 

On paper at least, the Mercedes does offer one of the best battery ranges against the Audi Q5 and BMW X3 PHEV variants, though we struggled to meet the claimed figure during mixed driving. Still, as long as you’re willing to keep the battery topped up, you are unlikely to find better fuel economy from an SUV as you will with the GLC 300 de. 

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2021 Mercedes-Benz GLC 300 de 4MATIC interior and infotainment 

Even though the interior of the Mercedes GLC is a bit long in the tooth and not quite as flashy as the company’s newer models, it remains a very nice cabin that fits the premium billing. The blend of pin-sharp touchscreen displays and materials like open-pore black ash wood ooze quality. An equivalent Audi Q5 feels more modern inside, and the BMW X3 is a match on quality, though the Mercedes nails that blend of new and old worlds coming together. 

All versions of the Mercedes-Benz GLC feature a 10.25-inch touchscreen display and runs on the company’s latest MBUX infotainment system. The trackpad is a bit fiddly to use and does take a bit of time to get used to but lacks the intuitiveness of BMW’s iDrive system. 

Opting for the AMG Line Premium (or higher) specification includes a neat augmented reality function for navigation. Using the front camera, it can show you in real-time which turn to take by superimposing directional arrows and even house numbers over a moving image. 

Smartphone users who prefer to stick with mirroring with either Apple CarPlay or Android Auto will need to go for AMG Line versions to get this feature as standard. All GLC models get the voice assist system that is activated by saying, “Hey, Mercedes”.

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2021 Mercedes-Benz GLC 300 de 4MATIC practicality and boot space 

You won’t have to look too far for somewhere to stow your oddments as the GLC’s cabin has places to put your things. The centre armrest opens on each side to reveal a deep storage compartment. A pair of USB-C ports are inside for keeping your smartphone charged up, and from AMG Line Premium there is a wireless charging facility. 

A pop-up cover within the centre console base reveals two cupholders and some more storage. Only the flat trackpad to control the infotainment system sits on the middle of the centre console as Mercedes uses the right lever behind the wheel as its drive selector for the 9-speed automatic. 

There is little in the way of compromise with the plug-in GLC, other than the noticeable step in the boot floor due to the battery. That drops the capacity down to 395 litres from the 550 litres that the non-hybrid models offer. The maximum capacity is 1,445 litres when the rear seats are tilted forward. Mercedes does include a helpful compartment that is ideal for storing the charging cables. All GLC models feature an electrically operated tailgate as standard. 

2021 Mercedes-Benz GLC 300 de 4MATIC battery, motors, range and charging

Mercedes is very much in the minority by offering a diesel plug-in hybrid. These are two expensive systems, but there is some merit to this setup as over long journeys the diesel engine can perform more efficiently at carrying the added weight of the battery system. The engine itself is a 2.0-litre four-cylinder that produces 192bhp and 400Nm. 

On the electrical side of the hybrid system is a 13.5kWh lithium-ion battery that is recharged via a small port in the rear bumper on the driver’s side. Using a domestic plug socket takes approximately five hours to recharge, but only 90 minutes when using a wallbox thanks to its 7.4kW onboard charger. Battery power goes to a 121bhp electric motor that drives through the nine-speed automatic transmission. According to official figures, the electric-only range is up to 27 miles, though the best we got from it was 20 miles, and that was with reasonably conservative mixed urban driving. 

The combined power output of the plug-in hybrid system is 302bhp and the GLC can travel in electric mode at up to 87mph, or 143mph with the diesel engine running. It can reach 62mph in 6.2 seconds from a standing start, making it one of the fastest non-AMG GLC models. 

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2021 Mercedes-Benz GLC 300 de 4MATIC driving

One of the main reasons you might consider the GLC 300 de is for that battery range and providing you are charging up at home or work and have the luxury of a relatively short commute. Between traffic lights, the electric motor gives the Mercedes a fair degree of pep with brisk acceleration thanks to its 440Nm of instantaneous torque. 

Over long distances, the Mercedes GLC delivers a faultless performance thanks to its comfort and refinement. Motorway driving is where the diesel engine works best and the nine-speed transmission helps its fuel-sipping nature. Comfort is another string to the GLC’s bow despite the presence of sport suspension as standard. The smaller 19-inch wheels in the base AMG Line specification do help add to softening the imperfections beneath. 

If, or rather when, the battery’s charge depletes, you will hardly notice much happening as it switches across to the diesel engine. This changeover is typically seamless with smoother-running and quieter petrol-engined plug-in hybrids, so credit to Mercedes for achieving similar results with the oil burner. 

Dave Humphreys

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