DOING less harm to the environment than an alternative petrol model but with no cost to performance is the underlying premise for Mazda’s new second-generation of Mazda6 diesel.

The new 2.2-litre turbo-diesel engine replaces the 2.0-litre model of the first-generation Mazda6 diesel, with more power and torque and lower emissions than its predecessor.

The new diesel has lagged behind its petrol counterpart, with the petrol version arriving in February. The diesel is available in two tiers of specification according to bodystyle: a lower-spec wagon or high-specification hatch.

Like the model before it, no automatic transmission is offered, although Mazda Australia managing director Doug Dickson admitted that diesel sales would improve if an auto were available.

Mazda Japan has said that it will renew its powertrains from 2011 so the possibility of an auto transmission is at least two years away.

The Mazda6 diesel is the only Japanese passenger medium diesel on the market until Subaru and Honda diesels arrive late next year. Direct competitors are sparse at the Six diesel wagon’s price point of $36,690, the closest being the Skoda Octavia Elegance TDI – albeit with much lower 103kW/320Nm outputs.

The $43,890 Mazda6 diesel Sports Hatch is lined up against a large group of potential candidates – on paper, at least – among the entry-level diesel Euro sedans and hatches, such as the Ford Mondeo, Peugeot 407, Renault Laguna, Skoda Octavia, Volvo S40 and Volkswagen Passat.

Of these cars, there is only one that shares similar outputs to the Mazda: the just-released Skoda Octavia RS TDI, which costs $39,490 in liftback form. While $4400 cheaper than the Mazda, the Octavia shares almost identical 0-100km/h performance and fuel consumption figures as the Mazda. Bodystyle, dimensions and standard equipment are also similar.

Mazda said it expects to sell 70 Mazda6 diesels a month, split roughly 50/50 between the two models. This represents just under 10 per cent of current Mazda6 petrol sales, going on an average of sales for the first 10 months of 2008, and 30 per cent fewer Diesel cars than the model it replaces.

Diesel passenger car sales have nearly doubled to business buyers in the first 10 months of this year while private-buyer sales are up a quarter over the same period last year.

The MZR-CD 2.2-litre, four-cylinder common-rail turbo-diesel engine is a new-generation engine, with variable geometry turbocharging and direct-injection and a diesel particulate filter.

There is a swag of features that Mazda claims drive the improvements: a low compression ratio of 16.3:1, made possible with highly-atomising injectors, for temperature cooling effect which contributes to low consumption a newly developed exhaust gas recirculation (EGR) cooler with superior cooling efficiency a new common-rail direct-injection system with injectors that have 10 spray holes (up from six on the MZR-CD 2.0-litre) and higher-response solenoids for power and low emissions.

The output figures are 136kW of power and 400Nm of torque, which are improvements of 31kW and 40Nm respectively on the 2.0-litre engine it replaces

That Mazda is not boasting much about the fuel cost savings gleaned by the diesel is understandable, given that with official combined figure of 5.9L/100km (wagon: 6.0L/100km) and the petrol Mazda6 manual’s figure of 8.6L/100km, at current fuel prices the Diesel owner can stand to save only about $200 every 10,000km. The petrol Mazda6 requires 95RON premium unleaded, that at the time of writing costs 112.4 cents per litre, while diesel cost an average of 133.7c/L.

At least the Mazda6 diesel pumps out fewer CO2 emissions, with a 156g/km figure for the sedan (wagon: 159g/km) compared with 204g/km for the petrol hatch.

At a claimed 8.5 seconds to accelerate to 100km/h, the diesel is just 0.5 seconds slower than the Mazda6 petrol’s claimed time. The 2.5-litre petrol four has 11kW less power and 174Nm less torque than the diesel, but its quicker acceleration times might be explained by its weight being between 100-150kg less than the equivalent Diesel model and that the diesel is slower getting off the line due to turbo lag.

Safety features are competitive, with six airbags, ABS brakes with EBD and brake assist, dynamic stability control, traction control, and anti-whiplash front head restraints.

The Mazda6 diesel wagon has as standard cruise control, keyless entry, tilt/telescopic steering wheel, front and rear power windows, 17-inch alloy wheels with a full-size alloy spare, foglamps, rain-sensing wipers, auto on/off headlamps, dual-zone climate control air-conditioning, leather-wrapped steering wheel, lumbar adjustment for the driver’s seat, trip computer, and a six-disc in-dash CD/MP3 player with six speakers, steering wheel-mounted audio controls and MP3 player connectivity.

Also standard is a feature Mazda calls ‘Cross-functional network’ (CF-Net), which is mounted in the steering wheel and enables easier control of audio, satellite-navigation (when optioned on Diesel Sports hatch), air-conditioning and trip computer

Mazda6 Diesel Sports hatch adds 18-inch alloy wheels, full leather interior, bi-Xenon headlights with Adaptive Front Lighting System (AFS), front and rear parking sensors, blackout instrument cluster, leather-wrapped gear knob, eight-way electrically adjustable driver’s seat with three-position memory and four-way electric adjustment on the passenger’s seat, and a Bose 240-watt sound system.

The only option available is satellite-navigation for the Sport hatch, at $2800.