The greenwashing files How fuel efficient are eco cars?
Are eco cars as fuel efficient as they claim to be?
There's an increasing demand for fuel-efficient cars in the UK - not surprising when you consider fluctuating fuel prices, the fact that road and company car tax are based on CO2 emissions and our growing awareness of the environmental impact of motoring.
In response, car-makers are producing an ever-expanding array of models that use new technology to improve efficiency and market themselves as 'greener' or 'eco' models. But are eco cars as fuel efficient as they claim - or are we being greenwashed? The results of our investigation show that not all eco cars are as fuel efficient as official figures claim.
Eco cars: testing fuel efficiency
Manufacturers establish a car's fuel economy by testing it to government standards. But this doesn't necessarily tell the full story, as the test only covers simple town and country road scenarios, not potentially petrol-guzzling activities such as cold-starting a car or driving on a motorway. So members of the Which? cars team decided to perform their own lab tests to find out how efficient some popular eco cars really are, using a cold start and motorway section to give a more realistic indication of real-world fuel economy.
Some eco cars can be streets ahead of their 'sister models' for efficiency - but some are only slightly more fuel efficient, and others didn't live up to their fuel consumption claims.
Eco cars investigation results
Ford Focus Econetic
Ford Focus 1.6 TDCi Econetic
Official average fuel economy: 65.6mpg
Which? measured fuel economy: 49.6mpg
This diesel, manual five-door hatchback is more frugal on the motorway than the Ford Focus diesel 2.0 TDCi, but you might not like its noisier engine and longer braking distance. Crucially, our testing revealed a lower mpg than the car's official fuel economy, meaning it's not as economical as it might appear. You'll save £18 on fuel every 10,000 miles compared with the 2.0 diesel.
Read our first drive review of the Ford Focus Econetic range.
Fiesta Econetic is Ford's most economical car
Ford Fiesta 1.6 TDCi Econetic
Official average fuel economy: 76.3mpg
Which? measured fuel economy: 62.8mpg
Our tests show the Econetic Fiesta diesel (three doors) is more economical than the conventional model, but you'll need to be prepared for longer stopping distances. Despite scoring over 76 miles to the gallon in government standard testing, it only scored 62.8mpg during our tests. You'll save £50 on fuel costs every 10,000 miles compared with the 1.6 TDCi three door Zetec.
Read our first drive review of the Ford Fiesta Econetic.
Toyota Prius hybrid
Toyota Prius 1.8 hybrid
Official average fuel economy: 72.4mpg
Which? measured fuel economy: 61.4mpg
The Toyota Prius is probably the best known 'greener' car, and the 2009 model certainly boasts a whole raft of fuel-saving features designed to improve efficiency. Again, our own 'real-life' testing recorded a lower fuel economy than it officially scored - however the Prius recorded a very impressive mpg when we took it for an informal 'eco' test drive where we were careful to drive in an economical way.
Read our first drive review of the Toyota Prius.
The Mercedes-Benz BlueEfficiency model
Mercedes-Benz C220CDI BlueEfficiency
Official average fuel economy: 58.9mpg
Which? measured fuel economy: 49.6mpg
Instead of choosing to develop a low-volume, high economy ‘halo car’, Mercedes has concentrated on improving efficiency standards for its highest-volume models, like this C-class four-door saloon. However our tests uncovered that its fuel economy wasn't as impressive as officially claimed. On the plus side, Mercedes hasn't upped the price on any of its BlueEfficiency models compared with their outgoing counterparts.
Read our first drive review of the Mercedes-Benz BlueEfficiency range.
Improved VW Passat Bluemotion 2
Volkswagen Passat 2.0TDI BlueMotion 2
Official average fuel economy: 57.6mpg
Which? measured fuel economy: 54.3mpg
VW's latest BlueMotion cars use 'second generation' technology, including a 'stop/start' system. This five-door estate BlueMotion model offers reasonable fuel and tax savings over a standard Volkswagen diesel, offering £135 worth of fuel savings over 10,000 miles. There was a small difference in the official and Which? measured miles to the gallon.
Find out more about the Volkswagen Passat BlueMotion 2 car.
Greener driving
Disappointingly, we've generally found that eco cars, like their standard car counterparts, deliver fewer savings than their makers claim. They're good for company car users looking to cut tax bills and can offer a more economical fuel option for drivers, but driving compromises and, in some cases, cost premium may prove too much for low-mileage drivers.
Improving your driving technique can be just as likely to cut your fuel bills and CO2 - take a look at our expert video guide to greener driving for more advice. Learning how to care for your tyres and how to keep your car in good condition all year round will also maximise its performance and efficiency.
