Which? Car first to test new Mercedes M-classExclusive full test of 2012 ML250 CDI diesel

08 February 2012

Which? Car is the first UK publication to fully test the new Mercedes-Benz M-class, which is launched in Britain in March 2012.

Controversially, the third-generation M-class uses a diesel engine with only four cylinders - a rarity in the luxury 4x4 class, which is dominated by six-cylinder diesels. The Which? Car tests confirm that the ML250 CDI is more economical than rivals, but suffers somewhat in performance terms. 

New Mercedes M-class aims for economy

Economy drive results in 38.2mpg

The reason for using only four cylinders is, says Mercedes-Benz, to boost fuel efficiency. The official combined-cycle fuel economy claim for the new ML250 CDI is 44.8mpg - an impressive figure. The Which? Car lab tests, however, revealed an overall average of rather less, at 38.2mpg.

That's still economical by full-size 4x4 standards, and beats the figures achieved by Which? Car for six-cylinder rivals like the BMW X5 30d and Volkswagen Touareg 3.0 TDI. 

It also means CO2 emissions are kept relatively low for a large 4x4. At 165g/km, you'll be paying £165 a year in VED tax.

Small diesel is up to the job - just

Is it up to the job?

Our testers also asked the question, are four cylinders enough for a luxury 4x4? With a mere 2.1 litres, the ML250 CDI cedes a fair amount of engine capacity to its six-cylinder rivals. The engine's peak power of 204bhp does, however, match the output of rivals like the Audi Q7 and Volkswagen Touareg in entry-level guise. 

With some 2150kg to haul around, the ML250 CDI has just enough performance. And for a four-cylinder diesel, our testers judged it as refined - just not as quiet or smooth as a V6 diesel. 

Mercedes-Benz also offers an ML350 CDI model with a 3.0-litre, 258bhp V6 diesel. 

£45,375 for four cylinders

The M-class goes on sale in the UK in March 2012 priced from £45,375 for the entry-level ML250 CDI Sport - making it among the most expensive four-cylinder cars on sale in the UK. 

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