REVIEW DATE: 23 Jun 2006
In The E320 CDI, Mercedes Has A Diesel Engine So Good That It Will Steal Sales From Pricier Petrol Models, Thinks Jonathan Crouch
As you'd expect from a company that virtually invented the diesel-engined saloon back in the Thirties, Mercedes knows a thing or two about making cars for this sector of the market. Having allowed neighbours BMW a brief period as diesel-meisters over the last decade, Stuttgart is attempting the wrestle market leadership back. And with the latest E320 CDI, they could well have the car to do it.
This is one of the latest generation of 'common rail' diesels which, in six cylinder form, arguably make more sense than their petrol counterparts. The straight-six direct injection unit develops a healthy 224bhp, enough to propel it to sixty in just 6.8s on the way to 155mph. Just as quick, in other words, as an E350 V6, a petrol-fuelled E-Class which, unaccountably, costs more. Asking prices for the E320 CDI start at £36,895 (or £38,695 for the estate version), nearly £4,000 more than the 190bhp E280 CDI variant which marks the next step down in diesel-powered E-Class ownership.
On the road however, this CDI sweeps all before it, thanks to an amazing 540Nm of torque, upped from 510Nm with the most recent set of revisions. This explosion of power means that almost instant acceleration is available in almost any gear, from as little as 1,600rpm. At this point, the standard automatic gearbox simply changes up and you're catapulted towards the horizon once more.
Thanks to common rail, it's quiet and frugal too (you should average over 38mpg in normal use). This is thanks to a system where fuel is precisely bled off from a highly-pressurised reservoir 'commonly' shared by every injector along the feedpipe or 'rail'. Exactly the correct amount of diesel is injected when required: not too much (hence the lack of the usual puff of black smoke on acceleration) but just enough to enable the car to respond to your slightest throttle feather.
"Owners used to big petrol V6s will find the E320 CDI to be a smoother drive..."
The result of all that pulling power is that owners used to big petrol V6s will find the E320 CDI to be a smoother drive, mainly because the advanced automatic gearbox has to do less shifting up and down. If you miss all that cog-swapping, you can drive it manually by tapping the selector to the left to downshift and to the right to change up, watching your gear selection via a digital indicator in the instrument cluster.
This 3.0-litre V6 diesel engine is part of the third generation of common-rail direct injection systems from Mercedes and excels with improved efficiency, smoother power delivery and reduced consumption, exhaust emissions and combustion noise. Light weight is also a key feature - this was the first all alloy diesel engine in its class, totalling only 208 kg.
The clever injector system it uses is equipped with fast acting piezo-ceramics, which have a response time of only 0.1 milliseconds. This new piezo technology means the normal number of fuel injections per power stroke has increased from three to five. To assist in a finer, and so more accurate, distribution of fuel, the common-rail pump pressure was increased from 1350 bar to 1600 bar. The combination of swifter injection and higher fuel pressure has led to Mercedes developing its unique pilot injection process. This introduces small amounts of fuel to the combustion process to preheat the combustion chambers. The result is a smoother combustion and reduced engine noise.
With a single turbo tucked into its Vee format, the compact and lightweight engine powers the E320 CDI through 7G-TRONIC automatic transmission. Speedtronic cruise control and the user-friendly Tipfunction are standard. 'Parameter Steering', 17in wheels and larger rubber aim to provide a sure footed package.
Mercedes took extensive measures to improve the quality of this E-Class, introducing more advanced technology across a number of its systems but it's not immediately apparent that the current model is such a heavily revised vehicle. True Merc anoraks may spot the front bumper, v-shaped grille and revised headlights but that's about it externally. Inside, it's more of the same with a revised steering wheel and climate control panel being about the size of it.
Under the skin, it's a different story. Handling and steering have been improved and the adaptive braking system has been borrowed from the S-Class. This hydraulic dual-circuit braking set-up provides better safety and comfort features. Safety is a standout E-Class feature and the latest models feature the PRE-SAFE system which primes the seatbelt and airbag if it thinks the car is about to be involved in a collision. The NECK-PRO head restraints move forward within milliseconds of a rear shunt, protecting the driver and front passenger from whiplash injuries. Flashing brake lights are also featured, illuminating during particularly heavy braking.
Go for the Estate model and total carrying capacity with all seats in place is 650 litres, while the payload is a useful 575kg. Your dealer will want you to pay extra for the optional 'EASY-PACK' retractable load compartment floor - an idea 'borrowed' from BMW's 5 Series Touring. Here, the base of the estate compartment can be moved 400mm towards you at the push of a button, allowing easier reach of items at the back of the boot or creating an optional picnic bench from which you can view Georgina's polo pony.
Overall, the E320 CDI certainly offers every encouragement to press on, a diesel you can really claim to have bought for the sheer joy of driving. Whoever would have thought it?
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