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Six is the best for Merc diesel

After a lot of fine-tuning, the second-generation Mercedes C-Class has matured into a deeply impressive car. But some of its engines are beginning to show their age, so Merc has developed this new four-valve-per-cylinder 3.0-litre V6 turbodiesel. Owing to its compact dimensions, it is the first six-cylinder diesel to find its way into the C-Class, where it replaces the old 2.7-litre in-line five-cylinder unit.

The engine uses an aluminium block and cylinder head to keep weight down. Boost is provided by a variable-vane turbocharger that works in combination with the latest piezo injector technology for more efficient blending of fuel and air.

The result is 221bhp at 3800rpm, but it is the torque that really moulds the driving experience. Mated to the standard six-speed manual gearbox, the new engine dishes up 306lb ft of torque between 1400 and 3800rpm. From the off it is refined and flexible, the engine barely perceptible under 3000rpm.

But it is even more impressive when attached to the optional seven-speed automatic gearbox, when the torque increases by 70lb ft to 376lb ft between 1600 and 2800rpm. The effect is dramatic, thrusting the C 320 CDI firmly into the performance-car ranks.

This is an awesomely quick car. Mercedes claims 0-62mph in 8.1sec for the manual and 6.9sec for the automatic, the added torque combining with more closely staked gear ratios to offset the weight of the bigger gearbox.

To fully appreciate the new engine’s achievements, however, it’s best to look at the 50mph to 75mph in-gear time of 6.2sec – the same time as the 362bhp 5.4-litre V8 C 55 AMG.

With thumping torque, strong economy (40.4mpg combined) and the C-Class’s excellent handling and cosseting ride, this is a breakthrough engine wrapped up in a hugely impressive junior exec.

Greg Kable

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