It was a largely flat and undemanding journey, unlike an earlier 190km run on the Great Ocean Road in a mix of sunshine and pelting rain and on good and bad surfaces.
The outgoing leg was in the ML 350 BlueTEC, its twin-turbo V6 diesel putting out 190kW/620Nm. Mercedes-Benz claims average fuel use of 7.3-litres/100km for the ML 350. Such a figure would indeed be possible in the right conditions, but we settled for the high eights - the better throttle response of the V6 made for more spirited driving. It gets to 100km/h about two seconds faster than the ML 250.
The four-cylinder unit is the result of the current buzzword "downsizing", where carmakers are using turbochargers to boost the power of thriftier smaller capacity engines to meet that of thirstier larger engines.
It's all to do with demands by European legislators for continuing cleaner burning vehicles. The Euro 5 emissions standard is in place now and Euro6 goes into effect in 2014. The ML 250 and its CO2 emissions rating of 168g/km already meets Euro 6.
The ML 250's output is well inside the average 197.1g/km of carbon dioxide emitted from new cars and light commercials sold in New Zealand last year.
It was the first time emissions have dropped below 200g/km. In 2008, the new vehicle fleet averaged 210.6g/km.
Two of the most significant factors in the country's sub-200g/km figure are a swing to smaller cars and the popularity of diesel engines in all cars, SUVs such as the ML 250, and light trucks.
The ML 250 went on sale in New Zealand last week and already the split in potential sales is showing.
The M-Class line-up picks up styling cues from the carmaker's sedan line-up, including the sculpted door panels, recognisable from the latest CLS, plus a swept-back headlight design and wide chrome grille borrowed from the CL.
The wheelbase is the same as its predecessor, but the slightly swollen overall size frees up more space in the five-seater cabin. There are more electronic aids, too.
Mercedes-Benz says special attention has been paid to using lightweight materials for the mudguards and front suspension, while the bodywork has been optimised to give class-leading aerodynamics. These green tweaks haven't sacrificed any of the M-Class's off-road abilities, says the carmaker.
The newcomer has six different transmission settings for the revised 7G Tronic gearbox, with two dedicated off-road modes.
Selective dampers, active anti-roll bars and locking diffs will also help when the going gets tough, and are available as part of an optional pack, but it is expensive.
A new system dubbed "active curve system" keeps the M-Class' body tightly controlled when cornering.
Inside, the cabin has a wide range of wood and leather finishes on offer, as well as advanced safety systems from the S-Class.
So what's it like, the ML 250 BlueTEC? The four-cylinder engine provides plenty of get-go and, allied to the seven-speed gearbox with torque converter, does a handsome job of hauling around the SUV's bulk.
The engine is refined and quiet, emitting only a low thrum at cruising speeds. Never at any stage is it particularly vocal.
The M-Class range rides on a platform with double wishbone suspension up front and a multi-link rear end. Steel springs are standard, coupled with adaptable dampers.
The optional Airmatic air suspension also comes with two selectable damping modes. Either way, handling remains taut and body roll in the big SUV is well controlled. Rough surfaces aren't exactly ironed out but the ride/handling mix is as good as you'd want in such a vehicle.
Green grunt
ML 250 BlueTEC - 2.1-litre twin-turbo four-cylinder diesel, 150kW/500Nm, 7-speed auto, 19-inch wheels, 6.4-litres/100km, 168g/km CO2 - $99,900.
ML 250 BlueTEC - Same as above but with extra goodies including air suspension and 21-inch wheels - $112,900.
ML 350 BlueTEC - 3-litre V6 single turbo diesel, 190kW/620Nm, 7-speed auto, 20-inch wheels, 7.3-litres/100km, 192g/km CO2 - $122,900.
ML 350 BlueEfficiency - 3.5-litre V6 naturally aspirated petrol, 225kW/370Nm, 7-speed auto, 20-inch wheels, 8.9 litres/100km, 208g/km CO2 - $122,900.
ML 500 - 4.7-litre twin-turbo V8, 300kW/600Nm, 7-speed auto, 20-inch wheels, 12.3 litres/100km, 287g/km CO2 - $150,900.
ML 63 AMG - 5.5-litre twin-turbo V8, 380kW/700Nm, 7-speed auto, 21-inch wheels, 11.8 litres/100km, 276g/km CO2 - $197,900.
All models have permanent all-wheel-drive; 93-litre fuel tank; stop-start fuel system on all but ML 350 BlueEfficiency and ML 500.
