Diesel — the name evokes images of smoke-spewing, heavy and crude vehicles whose only benefit is lower running costs due to diesel being cheaper than petrol. But that is not the case anymore.

Modern-day diesels are as good, if not better, than their petrol cousins in all respects. And if you’re driving diesels in a place which has a history of not being too kind to diesels, you know that diesels have indeed come a long way. We’re talking about Vermont, the US State that, along with California, has traditionally been super-strict on diesel cars.

We’re in pristine hills not too far from the Canadian border, driving a bunch of big, heavy diesels from Mercedes. But these are not your ordinary Merc diesels. Okay, the CDI common-rail diesel motors under the hood are basically the same. But Merc has carried out a set of modifications and fundamental exhaust after-treatment changes that together allow these diesel engines to be less polluting than a petrol motor. According to US law they have to be — they must adhere to the same basic petrol engine emission norms despite having a totally different emission profile.

Under the hood

So while diesel engines produce far less carbon monoxide, carbon dioxide and hydrocarbons than petrols, they have to be worked on to attain petrol engine-like particulate and nitrogen oxide emissions. While this loads the deck in favour of petrol-engined cars, diesels that can be made to adhere to the US’s Tier 2 Bin 5 norms are much cleaner cars overall, with emission standards at par with even some petrol hybrids.

The special equipment used on this BlueTEC M-Class I’m driving includes a particulate emission trap as well as the now common oxidation catalyst. (A particulate emission trap is a sort of filter that traps the larger particles of pollutants or soot that diesel vehicles emit. It is usually placed in the exhaust.) In addition, there’s the AdBlue or urea tank (from which these Mercs get their name), housed in the rear of the car, that helps reduce NOx (oxides of nitrogen) emissions. Liquid urea is added to the exhaust tract and is then stored in the SCR (Selective Catalytic Reduction) catalyst in the form of ammonia. This ammonia then combines with the nitrogen oxide released by the engine to produces harmless nitrogen (this car doesn’t use a De-NOx catalyst like the BlueTEC cars in Europe).

Driver’s deal

From behind the wheel, however, you simply have no idea that you are sitting atop a really hi-tech, electronically controlled chemical plant. Everything functions as normal; there are no extra controls, no warning buzzers, no flashing lights. The AdBlue tank needs to be topped up at service intervals, but this is a simple procedure, similar to topping off other fluids in the car.

Take the BlueTEC badge off, and you’ll think this is a normal M. That said, initial throttle responses on the 210 bhp diesel did feel a bit dull, before the SUV really takes off, making full use of that 55 kgm of torque. Smooth, very torquey and capable of delivering a good shove in the back, this diesel with its long stroke pistons is sure to appeal to anyone who appreciates effortless performance.

There’s no spare wheel at the back and none in the boot; the space is used up by the AdBlue canister, so this M Class rides on run-flat tyres. Still, unless you really pay attention, there is no real penalty. Ride quality even at low speeds is pretty impressive; the M displays that solid Mercedes-Benz feel even over bad bumps. And even on these 19-inch wheels, there is almost no thudding over poor sections.

On Vermont’s twisting back roads, the Merc also proved that it’s pretty adept at mixing it up with saloon cars. The handling cannot be compared with the sharpness of a BMW X5 or an Audi Q7, but the M is still a tidy handler. The steering is nice and sharp and the grip is very good, but you do get a sense of all that weight being flung around on the really twisty bits.

Inside story

With plenty of passenger legroom at the rear, improved plastic quality and a neat design to the dash, the M’s interiors are also a very welcome place to be in. You get that all-important ‘will last a 100 years without wear’ feel and this, combined with the general hush in the cabin delivers that special five-star experience. It remains a five-seater though.

Final verdict

Mercedes has proved that diesel engines can be cleaner and more efficient than petrol engines. And there is a diesel BlueTEC Hybrid on its way, which will make life difficult for petrol hybrids. It is unlikely that India will get the BlueTEC M-Class anytime soon. But it is an indication of things to come, that diesel is only going to get better.

Spec Check

Mercedes-Benz ML320 BlueTEC

Length/ Width / Height: 4780/1911/1815m m

Wheelbase: 2915mm

Turning circle: 11.75m

Engine: V6, 2987cc, diesel

Installation: Front, longitudinal

Power: 210bhp at 3400rpm

Torque: 55kgm at 1600-2400rpm

Gearbox: 7-speed automatic

Fuel tank: 95 litres

Tyres: 255/50 R19