Swedish marque Volvo has been interested in caring for the environment for much longer than most other makers, so the introduction of a pair of new ultra-clean diesel engines is an important occasion.

The first of the new generation powerplants is a 2.0-litre four-cylinder unit, the other a fascinating 2.5-litre five-cylinder tagged the D5.

The four-cylinder unit is installed in the smaller models in the current Volvo range, the C30 coupe, S40 four-door sedan and V50 five-door station wagon. It replaces older versions of the D5 engine, but offers similar performance to that superseded engine and has significantly lower fuel consumption and reduced emissions.

With fuel consumption of six to seven litres per hundred kilometres when measured on the combined Australian driving cycle it's an impressively clean engine.

For exact details of fuel consumption on individual models may we suggest you contact a Volvo dealer. You may also be impressed with the fact that Volvo has trimmed the prices of its model range for 2010.

Complementing the new four-cylinder turbo-diesel is a Getrag double-clutch gearbox that further improves the efficiency of the overall drivetrain. We carried out an introductory test drive of the 2010 Volvo C30 diesel and came away impressed with the smoothness of the powerplant and its willingness to rev after a minimum of turbo lag.

The double-clutch transmission has the usual hesitation at very low speeds that's a feature of this type of gearbox at present, but is presumably going to be sorted out in later generations. In the meantime the transmission offers better acceleration and lower fuel consumption than that of a full-manual gearbox.

Smoother and quieter running is another feature of this new Volvo diesel engine and this gives the already good small cars a further boost in the refinement stakes.

The new Volvo five-cylinder, common-rail turbo-diesel engine has a capacity of 2.4 litres. It produces 151 kilowatts, and 420 Newton metres between 1500 and 3250 revs. All this is available thanks to the use of twin turbochargers. These are excellent numbers for any diesel engine and would have required a large thirsty petrol engine only a few years back.

Instead the typical fuel consumption of the new five-cylinder Volvo diesel is in the seven to eight litres range by official Australian standards. This consumption is about half of that of the aforementioned big petrol engines. Yet our initial test drive of this new engine in a Volvo V70 wagon showed the car to have acceleration off the line and when overtaking that's not far short of that of old-style petrol V8s.

Response from the new twin-turbo engine is excellent, with a minimum of lag as the smaller turbo spins rapidly from relatively low engine speeds. Thus allowing the second, larger turbo to provide less boost, until it's needed at higher revs, when it starts to provide that aforementioned big torque.

Volvo is fitting the 2.4-litre twin-turbo diesel to its larger all-wheel-drive models, the Volvo XC60 SUV, XC70 wagon and the topline S80 saloon. However the engine isn't offered in the current Volvo XC90 as it's an older design and a lot of re-engineering would be required to install it. It will presumably be offered in the next XC90, which can't be too far off. But Volvo won't comment on upcoming models.

The only model we have driven with the new D5 engine at this stage is the XC60. We were again impressed by the refined feel of the complete vehicle, a feel that's enhanced by the new engine. And by the quality of finish of the complete SUV.

The range of Volvo models with the new diesel engines, excluding dealer and government charges, is as follows. Prices of the outgoing engines are in brackets.
C30 2.0D automatic: $37,950 (D5: $43,950)
S40 2.0D automatic: $42,950 (D5: $44,950)
V50 2.0D automatic: $45,950 (D5: $47,950)
XC60 D5 automatic: $58,950 ($57,950)
XC70 D5 automatic: $61,950 ($60,950)
S80 D5 AWD automatic: $79,950 (2WD: $72,950)