Fastest non-AMG M-class is hard to justify

The turbodiesel version of the new Mercedes M-class saw off the best the highly competitive luxury 4x4 sector has to offer when we group tested it two weeks ago. For most buyers, that’s all they’ll need to know – over 60 per cent of outgoing ML sales were 270 CDi diesels, and that figure is likely to rise with the arrival of the powerful, refined new 3.0-litre V6 diesel.

But there remains a small pocket of British buyers – and a whole sackful in the USA – for whom the pace and prestige of large-capacity V8 petrol 4x4s still appeal. And if it’s an M-class they want, then this ML 500 is as ostentatious as it gets until the 6.3-litre AMG version arrives late next year.

Unlike the new V6s, the 4966cc V8 is carried over from the old M-class, though power has been boosted from 292bhp to 302bhp and torque is up 15lb ft to 339lb ft. That’s still not as much as the 320 diesel (376lb ft), but the V8’s extra 81bhp tells in the performance figures – its 6.9sec 0-62mph sprint is 1.7sec faster and it runs out of steam 15mph later at 149mph. In practical terms, the diesel’s extra mid-range punch makes it feel little slower, though the V8’s willingness to rev makes it a more effective overtaking tool.

This most expensive M-class builds on the already impressive refinement of other models. The V8 is exceptionally quiet at low revs, and spins smoothly towards the red line and another shunt-free gearchange from the standard seven-speed automatic ’box.

Our test car featured Airmatic suspension and optional 19-inch wheels (18-inchers are standard), and rode serenely in both Normal and Comfort modes. Select Sport and the adaptive dampers firm up noticeably to give BMW X5-rivalling body control. The ride gets much firmer at the same time, but without the uncomfortable choppiness of a similarly set-up Volkswagen Touareg.

We weren’t given the opportunity to find out how the standard 4-ETS permanent four-wheel-drive system copes off-road, but did try a car fitted with the optional Off-Road Pro package. With locking central and rear differentials, a two-speed transfer ’box, additional ground clearance and more off-road-orientated tyres, it was a remarkably capable mountain climber.

While the V6 petrol ML 350 struggles to make a case for itself against the similarly priced diesel, the 500 feels like a genuine range-topper. Standard equipment in the V8 includes air suspension, leather seats, 18-inch wheels, multi-zone climate control and ventilated rear disc brakes, but it’s likely to be around £10,000 more than the diesel.

The ML 500 is noticeably faster and more refined than the 320 CDi, and nearly as torquey, but with claimed fuel consumption of just 21.1mpg (30.1) it’ll need three tankfuls of petrol to every two tanks the diesel sips. Unless you must have petrol power, we’d go for the oil-burner.

Alastair Clements

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