Audi A4 2.0 TDI e

Rating: 3/5

Think-green motoring and big-ticket items such as hybrid drivetrains and battery-electric vehicles often hog the headlines.

But there are less-conspicuous ways to cut fuel use, as Audi's A4 TDI e demonstrates. Using aids that earn this model the little green "e" tag, this A4 claims a 4.8 litres per 100 kilometre fuel-use average, with no electric motor in sight.

What do you get?

The TDI e's primary fuel-saving feature is what Audi calls "start-stop" - pull up, slot the gear lever into neutral, release the clutch and the 2.0-litre turbo diesel engine stops. Push down on the clutch again and the engine fires up. Audi says this technology can save up to 1.5L/100km in city traffic and about 0.2L/100km on the highway.

The rest of the package includes taller gear ratios, a "kinetic energy recovery" system that lowers the alternator's demand on the engine, aerodynamic tweaks to make the A4 more slippery through the air and a driver-efficiency program that suggests when to change gear and shows the level of electrical drag from accessories such as the dual airconditioning and headlights.

So, how does that 4.8L/100km claim compare? BMW's new manual-only 320d coupe - also with a stop-start function - undercuts it with a claimed 4.7L/100km average (the sedan, which doesn't yet get that feature, averages 5.3L/100km), while the best Mercedes-Benz C-Class, the C220 CDI, officially averages 6.2L/100km.

The price - $51,100 plus on-road and dealer costs - slips under the $57,466 luxury-car tax threshold.

Highlights include leather trim, cruise control, 10-speaker single-CD audio, an electric parking brake, foglights and 16-inch alloy wheels. There is no automatic option; the start-stop system is manual only.

If that looks a bit thin, then the safety equipment compensates. Front, side and curtain airbags, stability control and anti-lock brakes are standard. The A4 is also a five-star Euro NCAP performer.

What's inside?

By Audi's standards, the interior of the TDI e is almost downmarket. Even so, it exceeds the best of most of the rest. There are obvious hard surfaces and a lack of fancy accessories but it still offers appropriate legibility, adjustability and comfort.

There is plenty of room and the boot is enormous. Remember, this is a big car - 4.7 metres, making the lack of rear parking sensors obvious - while the front-wheel-drive layout equates to packaging efficiency.

There's no shortage of storage options, with large door pockets for the front seats and a decent-sized glovebox.

Under the bonnet

We tallied 1000 kilometres in the TDI e, doing everything from stop-start city traffic to freeway cruising, with the final fuel-use average ending up at 6.0L/100km. It's not quite what's claimed but it's still good.

The fuel gauge's slow decline was the only glacial thing about the TDI e. With peak torque available from 1750rpm-2500rpm, the twin-cam, direct-injected, turbocharged and intercooled engine gave a strong performance.

It was happy to rev close to 5000rpm (that's high for a diesel) and never exhibited any roughness and very little turbo lag.

However, the manual gearbox would drive you mad around town, especially combined with the stop-start system.

Go for a snappy launch from stationary and it's possible to be in gear and attempting to accelerate before start-stop gets its act together. As a result, you can suddenly and inelegantly stall the engine.

On the road

The TDI e displays the likeable fundamentals of the others in the A4 range. It's supple over ruggedly bumpy roads but doesn't feel loose or vague. It's a nice compromise and a different proposition to, say, the sportier feel of a BMW.

That contrast continues in the steering, which is very light for slow-speed work but ramps up as speed climbs.

The TDI e is noisier than how we remember the standard A4 TDI, which suggests it may have lost some noise insulation in the interests of weight control.

Still, the A4 is relaxing enough to be a great country cruiser.

Verdict

The economical technology of the A4 TDI e is good but the start-stop stop-start system will be a better proposition with a dual-clutch or automatic transmission.

Until then, buying this car means you really need to be keen to be green.

At a glance

How much? From $51,100 plus on-road and dealer costs

Engine 2.0-litre 4-cyl turbo diesel with stop-start function

Power 100kW at 4200rpm

Torque 320Nm at 1750rpm-2500rpm

Fuel use and emissions 4.8L/100km and 124g/km CO2

Transmission 6-sp manual

Weight 1475kg

Safety 6 airbags, 5-star Euro NCAP rating

Pros Good fuel economy; classy fit and finish.

Cons No automatic gearbox; stop-start system needs refinement.

The competitors

BMW 320d Lifestyle

From $59,100 plus on-road and dealer costs. 2.0-litre 4-cyl turbo diesel; 135kW/380Nm; 6-sp auto; 5.3L/100km and 140g/km CO2; RWD. Updated in 2009. Sharp real-world fuel economy. No manual option. Stop-start only on Coupe. Not yet rated.

Mercedes-Benz C220 CDI

From $61,400 plus on-road and dealer costs. 2.1-litre 4-cyl turbo diesel; 125kW/400Nm; 5-sp auto; 6.3L/100km and 164g/km CO2; RWD. Powerful and frugal drivetrain; best-handling C-Class yet. Average load space. RATING: 4/5

Lexus IS250

From $55,900 plus on-road and dealer costs. 2.5-litre V6; 153kW/252Nm; 6-sp auto; 9.1L/100km and 214g/km CO2; RWD. Good value and equipment levels; quality and refinement. Firm ride; no diesel engine. RATING: 3.5/5

For more on the Audi A4, go to drive.com.au/audi