4x4s tested: Lexus hybrid v Mercedes diesel

You would think that owning a posh off-road car would be a pleasant experience. But with greenies queuing up on one side to pelt 4x4 owners with eggs, and politicians on the other ready to strip their wallets faster than a mugger, the temptation to run one of these cars is disappearing fast.

Yet there are ways to own a large 4x4 and not feel guilty about the melting polar ice caps and unseasonable weather. The first option is to go diesel. Compared to equivalent petrol models, diesels tend to have lower emissions and improved fuel economy.

Green motoring: do we really care?

The Mercedes ML320 CDI is one of the best in class and is a huge improvement over the car it replaced. We rate its strong engine, plush cabin and comfortable ride. Challenging it is a less conventional choice, a hybrid 4x4 – and the only one currently available is the Lexus RX400h.

This petrol-electric space-traveller boasts the performance of a V8 without the crippling fuel bills. But for the best all-round test of these cars we headed to the natural home of the posh 4x4, deepest suburbia. And unsurprisingly our journey took us to the London borough of Richmond, where radical moves have been put in place to drive its residents out of 4x4s through excessive parking charges. But would the traditional Mercedes, or the futuristic Lexus, prove these charges unfair, and which of them would be the most convincing as a green choice?

Driven: Lexus GS450h hybrid saloon

Ian's view of the Lexus RX400h

The eco-mentalist cyclists hurling abuse at our 4x4 double act clearly did not appreciate their apparent green merits. Now I have nothing against bikes. If anything, I am quite partial to a spot of pedal action as a means of relieving the stress of a busy day. But my Lycra-wearing friends could not spot a wind turbine from 100 paces, because they were hurling abuse at the wrong car. The Lexus RX400h is allegedly the most environmentally-sound luxury SUV money can buy. Indeed, so silent is its petrol-electric engine, I was able to make out every ‘f’, ‘w’ and ‘b’ in their rage-induced rants.

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Henry wasn’t getting an easier time in the diesel - and I must point out - less eco-friendly Merc. The insults were soon flying in his direction. But we were not going to let a bunch of opinionated cyclists stand in the way of a thorough MSN Cars assessment. Despite the clear hostility towards 4x4s in Richmond – the angry cyclists and the £300 parking charge for residents – the place is full of the things, especially those that carry posh Range Rover, BMW X5 and Mercedes ML badges. Yet strangely, there were few RX400hs, despite its supposed financial rewards.

So what are these benefits? Well, thanks to relatively low carbon dioxide emissions of 192g/km, the RX400h is cleaner than every comparable rival. It is actually similar in output to an Audi A4 2.0-litre petrol, which is good news for company car drivers keen on having a flash 4x4 but low tax bills – and a clean(ish) conscience. Even London Mayor Ken Livingstone reckons the RX400h is something special. He has granted this 4x4 exemption from the London congestion zone thanks to the electric components that allow the Lexus to glide around cleanly at low speeds.

Will hybrids save the planet?

But the idea that a giant Lexus 4x4 can drive in the congestion zone for free, while the driver of a diesel supermini has to pay the same as flash Harry in his Ferrari or estate agent boy in his BMW 3-Series, has clearly niggled his conscience. Because Transport for London is currently looking at proposals to radically overhaul the congestion charge system in line with car emissions. One of the options being considered is to offer free congestion zone travel for cars in bands A and B, which is those that emit less than 120g/km.

This means a lot of superminis will be free, while cars that emit more than 225g/km and sit in Band G, most large petrol 4x4s, saloons and sports cars will be hit hard. Luckily, the Lexus does not fall into this latter category, but its drivers will have to pay the charge if the plans go ahead. Free congestion travel is not the only reason why someone would buy an RX400h, though. Putting aside for the moment its comfort, space and prestige, this Lexus is seriously quick. Made up of a battery pack and a 3.2-litre V6 petrol engine, it earns its green medal because it conserves the energy released through accelerating, braking, friction and so on and stores this in the batteries.

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When you are pootling around town, the stored electricity is used to power the car without the need for the petrol engine, hence cutting down on harmful emissions and boosting fuel economy. But do not even think this car is a slouch as a result of this green-fangled technology. Stick your foot to the floor and the electric motors combine with the V6 petrol engine to thrust the car forward at a quite remarkable rate. The result is a 0-60mph time in the mid-sevens, thanks to the peak torque delivery from low revs.

The downside of this prodigious low-down shove is that the front wheels can be found scrabbling for grip, causing the steering wheel to wriggle in your hands. It isn’t really a problem, just a bit unnerving when you first encounter it. Then there is the noise. While it is deathly silent at low speeds, when you up the pace the engine takes on a growl that would be pleasing were it not for the CVT gearbox which has no discernible shift in ratios or resonance. The result is an engine that sounds one-geared, like a washing machine on a fast spin.

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The Mercedes, in comparison, feels just as powerful thanks to a great slug of torque from low revs, although the delivery from the turbodiesel engine is not as smooth or linear as the Lexus’ petrol-electric combo. The ML sounds coarser too. As for the ways these cars drive, neither can be hustled along like a saloon, but both do a great job of harnessing their weight and size. The Lexus’ body rolls in bends, as you would expect, but unless you corner like a rally driver, you will not have any problems. Likewise the ride. It is a bit firm at low speeds but it becomes more soothing as the pace increases.

We cannot review these cars and not come on to the sticky subject of fuel economy. Lexus quotes 34.9mpg for the RX400h on the combined fuel cycle, which makes it slightly more economical than a lot of equivalent diesel SUVs, 5mpg better than the Merc and a lot better than any V8-engined 4X4. However, throughout our test it was hard to better 29mpg, which is still impressive for such a large, fast car, but it is still a long way short of what I would call ‘green’. Now a diesel-hybrid would be the way forward; green and lean!

Top 10 fuel saving tips

As for price, we tested the range-topping SE-L at £45,258 – which is a lot considering the Merc costs £39,970 list. But then I ran my finger down the spec for the ML and found that, with the options on our test car, its price rises to a fairly hefty £48,750. And this is the advantage of the Lexus, its well-stocked cabin. There really is everything you could ever need in here, from a colour-screen parking monitor, to a quality sound system, electric seats, leather chairs and sat nav. Mercedes has you paying for a lot of this kit, and you really get hammered for it.

We set out to see which of these two large 4x4s would be the best ownership proposition in these SUV-hating, ‘save the planet’ times. As we have discovered, neither really fit the bill, but Lexus is certainly striving in the right direction with the RX. The technology is great, turning what would be a very uneconomical 4x4 into a fairly green alternative. It is massively quick as well, proving that going down the green route does not mean you have to settle for dull cars, and it is as plush as any car sitting on the sensible side of a Bentley Arnage.

But I cannot help feeling that if someone brought out a diesel hybrid, the market really would be cornered.

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Henry's view of the Mercedes ML320CDI

I admit the choice of Richmond as a location for this test was a deliberately provocative one but not intended, as you might think from Ian’s account, to annoy cyclists. Yes, Richmond council’s recent decision, sure to be adopted by many others, to treble parking charges for SUVs is odious. After all cars emit absolutely no carbon dioxide when parked, unlike, for the sake of argument, cyclists. But equally bizarre and perhaps even distasteful is the current vogue for urban SUVs.

Now I have absolutely nothing against 4x4s. I grew up driving some distinctly agricultural old Discoveries and Range Rovers, which my family owned because of the need to transport bales of hay - and never for the school run. Mainly because they were uncomfortable, slow and smelled of wet dogs, but that’s beside the point. How things have changed. The average modern SUV is more likely to smell of the grande gingerbread soya latte, purchased while the beast is double parked outside Starbucks and drunk on the move, the scalding hot coffee juggled with a mobile phone by a small lady in large sunglasses and bottle blond hair.

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And as owners have become less and less interested in the actual all-terrain abilities of their corpulent off-roaders and rather more interested in how fast they are able to tailgate someone in the outside lane of the motorway, so SUVs have evolved into ever more irrelevant vehicles, incapable of performing the tasks this type of vehicle was invented for. The Lexus RX400h is an unconscionable salve to a guilty conscience, allowing owners to lord it over other road users and then when challenged on environmental grounds, to point to the hybrid badges on the flanks. It is smugness squared.

The RX400h lacks the low-ratio gearbox and other systems such as locking-diffs that would allow it to actually go off-road. Yet it not only lugs around the unnecessary weight of a largely useless four-wheel drive system, it has to contend with a heavy battery pack and auxiliary electric motor. And this is supposed to be a green car? Added to this, research suggests that any reduction in CO2 emissions achieved by a hybrid vehicle over its working life are likely to be offset by highly energy intensive manufacturing and end-of-life recycling processes and any hybrid, particularly an SUV, starts to look like a spectacular case of PR over practicality.

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Which is where the ML scores, thanks to the fact that it is actually capable of tackling genuine rough terrain thanks to full-time four-wheel-drive and clever electronics to allow it to climb slippery slopes. Admittedly genuine mud-plugging ability will require the forking out of an extra £1,320 for the off-road pack, comprising low-ratio gearbox and locking centre and rear differentials. No doubt most owners will tick the off-road styling package option whichever four-wheel drive package they plump for, the cheese-grater grille and aluminium bash plates adding presence to what is already a handsome vehicle.

How to drive off-road

It also drives far better than the old ML, which was itself one of the first of the new breed of full sized SUVs to offer anything approaching car-like driving characteristics. The ML feels commendably stable at motorway speeds, a comfort to any owner who may have read recent reports that SUVs are twice as likely to overturn in an accident. The ride is also exemplary thanks in part to the balloon-like tyres but also the optional air-suspension fitted to our test car, an expensive option at £1,265 but worth it for the SUVs habitual urban habitat with its potholed roads and vicious speed bumps.

Mercedes-Benz’s 3.0-litre V6 turbodiesel is one of the finest DERV drinkers in the world with 220bhp and, more importantly, 376lb/ft of torque, comfortably more than that produced by the 5.0-litre petrol V8 in the ML500. Mated to the seven-speed automatic gearbox, it gives the ML the sort of unburstable, drive-me-across-a-desert feel that characterises the best SUVs and endows it with a fair turn of speed. Permanent four-wheel-drive also means the ML has no problem handling the power, unlike the RX which torque steers like an ‘80s hot hatch, rather unseemly in a luxury 4x4.

Driven: Mercedes GL450

The interior of the ML is also a far more pleasant place to spend time insulating oneself from the opprobrium of other road users. The RX may boast a multifunction display screen able to tell you exactly where the power is being distributed between the various batteries and motors but unfortunately it is mounted in a sliver-trimmed centre console that looks like a cheap hi-fi. Completing this look is, believe it or not, a cassette player. Why not an auxiliary socket for an MP3 player Lexus?

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Mercedes seems to be taking a leaf out of the Audi design book with grab handles either side of the centre console, chrome ringed dials and wood trim that looks like it at least had passing acquaintance with a tree. The column mounted auto-shifter takes some getting used to but it at least allows the car to be popped easily into Park at traffic lights rather than dazzling following drivers with the brake lights. What does let the ML down is the unyielding nature of some of the plastics, particularly in high-contact places like the door tops and admittedly much of the kit that is standard in the Lexus is a costly option in the Mercedes.

Neither of these cars are Sports Utility Vehicles. A two and a half tonne behemoth will never handle like a Lotus, no matter who builds it or what technology is under the surface. The Lexus may be quicker but it is unruly in a straight line and wallows in corners while its off-road prowess is woeful. The combination of torquey diesel and a large spread of gears in the Mercedes creates a relaxed cruiser with the ability to tow horseboxes, boats and caravans. If you really need an SUV, it’s the one to go for but if you’re honest, you probably don’t.

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Why I love my 4x4
Britain's love affair with the 4x4 may be over
Our green motoring section
4x4 drivers more likely to flout the law
Group (with video) roadtest of the Audi Q7 v Mercedes-Benz GL v Land Rover Range Rover
Used Car Guide: compact 4x4s