At idle, the engine emits only a distant rumble; as revs rise it becomes quite loud, but doesn’t turn coarse. There’s minimal turbo lag, and strong, steady shove is available all the way from 2000rpm to the upshift point just below 5000rpm.
The nine-speed automatic gearbox (the only available transmission) manages progress well. It splashes serenely through the ratios in town, where choosing the drive control’s miserly Eco mode keeps revs low to subdue the engine. Firm suspension disrupts the peace, though, thumping over ridges in a controlled but hard-edged manner that’s exacerbated by our car’s optional 20-inch wheels.
At 70mph in ninth gear, the crankshaft turns at just 1500rpm, and while the engine’s distant rumble persists, the GLC is refined at a cruise save for tyre roar over coarser motorway surfaces.
The car is game for B-road sorties, too. There’s a fluidity to the body control that’s genuinely enjoyable as you leverage the 250 d’s 74lb ft advantage over the 220 d between corners and its traction-bearing four-wheel-drive system through them. Sport mode makes the gearbox’s shifts more aggressive, but there’s still a delay between requesting a manual shift on the steering wheel-mounted paddles and getting it.
The steering is a more serious gripe, though. It’s overly light in Comfort mode, and while it’s responsive enough and there’s more heft to the helm in Sport, there’s a lack of weight variation, which muddies messages of grip from the front wheels. The brakes disappoint, too - they’re certainly effective but have a wooden pedal feel.
Should I buy one?
The adaptively damped GLC with air springs we drove impressed for handling and comfort, so there seems little call for the AMG Line’s firmer passive set-up. You can add air suspension to mid-range Sport specification for the same price as upgrading to AMG Line, and that seems the smarter move.
Sport is the only trim eligible for the £495 off-road pack, too, adding tools such as hill descent control, 20mm-raised suspension, underside engine guard and special traction programmes.
Official figures say there are no emissions or combined economy disadvantages to choosing the 250 d over the 220 d, meaning it beats the slightly thirstier and slower BMW X3 xDrive20d which, in M Sport trim with an auto gearbox, costs within a tenner of the GLC 250 d AMG Line. Given the Mercedes’s superior refinement and fresher interior, the X3 definitely has a battle on its hands.
Mercedes GLC 250 d 4Matic AMG Line
Location Bedfordshire; On sale Now; Price £39,595; Engine 4 cyls, 2143cc, twin-turbocharged, diesel; Power 201bhp at 3800rpm; Torque 369lb ft at 1600-1800rpm; Gearbox 9-spd automatic; Kerb weight 1845kg; Top speed 143mph; 0-62mph 7.6sec; Economy 56.5mpg (combined); CO2/tax band 129g/km, 23%