The BMW 320d EfficientDynamics saloon

The swingometer is veering rapidly and wildly, throwing up numbers hard to believe. Had it been measuring trends on general election night, prospective MPs of all stripes would have wound up gibbering wrecks. What this particular swingometer is telling us now is something altogether different. Dashboard-mounted, it is serving notice that we are behind the wheel of one of the most significant, competent and in its own way exciting cars ever to come off a BMW production line.

Just for once, forget all that car enthusiast’s guff about scorching 0-60mph times; expensive (and all too often barely used) toys and gadgets, or even good looks, although it is actually a rather handsome piece of machinery. Concentrate instead on the continuous, real-time read-out of fuel consumption the swingometer is providing as we sweep through the villages and forests of BMW’s native Bavaria. The needle veers between 10mpg and 90mpg, showing all too starkly how fuel consumption soars under hard acceleration and how frugally it can be used in gentle, top-gear cruising.

And what we are being informed of specifically is that this spacious, comfortable, well-equipped and still-rapid (142mph) executive saloon is averaging 60mpg. I have not the slightest doubt that, driven with only a modicum of restraint and still cruising at typical UK motorway speeds, the usually optimistic “official” EU urban/rural test cycle consumption figure, in this case 68.9 miles from a gallon, could be achieved with ease.

Equally impressive, the BMW 320d EfficientDynamics saloon – to use its official tongue-mangler of a name – is emitting just 109g of globe-warming CO2, an unprecedentedly low figure for almost a tonne and a half of executive express. That makes it the first car in the executive sector to warrant a bill for a mere £35-a-year road tax in the UK, while qualifying it also for a rare 100 per cent first-year capital allowance write-down for companies.

In terms of economy and environment, this is entering new and virtuous territory for business cars. So it is, presumably, a hybrid? No it isn’t. It is powered entirely by a 2-litre diesel engine and on every count but one it puts overly praised hybrids to shame.

Autocar magazine, in one of its deeply detailed and exhaustively analysed group tests, has just rammed the point home. It lined the BMW up against four other wheeled eco-warriors, some much smaller, lighter and cheaper. The BMW knocked them all for six, with the only executive sector rival, the notoriously frugal 2-litre Mercedes-Benz C220CDi BlueEfficiency saloon, trailing 6mpg-10mpg behind and emitting 127g of CO2 per km. Only in terms of the ability of hybrids to creep along in traffic entirely on pollution-free battery power alone does the BMW lose out.

The formula for achieving such modest fuel consumption is a long and fairly complex one and should be pored over by every carmaker. Because this really is major fuel economy gain for very little pain in terms of lost performance or driving pleasure.

The 320d EfficientDynamics is part of a newly updated range of 3-Series models, the most popular businessman’s express in the UK. They look very little different from the outgoing models but even the standard (non-EfficientDynamics) 2-litre diesel gets engine stop-start for urban crawling and provides the driver with the discretion to switch off air-conditioning compressor, power steering and other energy-consuming systems when not strictly needed. The EfficientDynamics model goes further, with raised gearing, low rolling resistance tyres, balanced engine, trick flywheel to iron out vibrations, lowered suspension and a few aerodynamic tweaks to help it slip through the air more easily. The one and only seemingly large downside is that engine horsepower is reduced, by nearly 20 to 163bhp, compared with the standard 2-litre diesel, in pursuit of further economy.

Except that, out on the highway, it barely seems to matter. There remains plenty of torque, while acceleration from standstill in 8.2 seconds is still enough to dispatch any would-be 2-litre diesel rivals. The 3-Series’ class-leading handling is still there and it remains very much a sports saloon. It is only on long, slightly uphill motorway stretches that the very high gearing means that some drivers will feel the need to drop down from the sixth of the manual gears to fifth more readily than is the case with the more powerful 2-litre diesel, in order to maintain momentum. And while there is also a (non-intrusive) sense of more cabin noise, as if weight-saving has been part of the formula, BMW insists this is not the case.

So how much more than the standard 2-litre diesel will the 320d EfficientDynamics version cost, given its fuel bill-transforming potential for higher-mileage drivers and the new benchmark it is setting in terms of environmental credentials? The answer is: nothing, zero, zilch. The basic price of £27,245 is identical to the “standard”, higher-powered model. It is a case of what is most important to you – performance or economy? You simply pay your money and you take your pick.

For now, the EfficientDynamics 3-Series is offered only as a saloon and BMW executives are putting on a great show of modesty about predicting whether it will be a sales success. That is rubbish. BMW might have lost its way a bit recently in terms of the handling and dynamics of its mainstream petrol saloon and sports car ranges. But with this radical new diesel it is on to a thoroughly deserving winner. The EfficientDynamics technology, one can predict with absolute confidence, will soon be spreading through the rest of its range like the proverbial rash. Other carmakers will have to follow suit.

The details

BMW 320d Efficient Dynamics saloon

How much?

From £27,245

How fast?

0-62mph 8.2 secs, top speed 142mph

How thirsty?

68.9mpg on EU urban/rural test cycle

How green?

109g/km CO2

Also consider

Mercedes-Benz C220 CDiBlueEfficiency, from £25,920

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