Which? reveals the real cost of running a diesel car

Despite superior fuel economy and usually lower car tax, a Which? investigation has found that diesel cars are often more expensive to run than petrol cars.

This year is set to be the first in which diesel cars will make up more than half the new car market. However, a Which? comparison of diesel and petrol versions of six popular car models has found that petrol engines can often be the more cost effective choice for drivers covering a typical annual mileage.
Diesel engines in the popular BMW 5 Series, Ford Fiesta, Vauxhall Astra, and Volkswagen Tiguan may deliver cheaper fuel bills than their petrol counterparts initially but it takes many years before they actually save the average driver1 money.

With drivers having to pay a premium for a diesel car – typically £1,000 to £2,000 more on a new car – our tests reveal that it could take up to 14 years to recoup the upfront costs in fuel savings. Lower pump prices for petrol and advances in petrol-engine efficiency mean that petrol cars now often provide better value for money.

Which?’s own fuel-economy tests also often fell short of the manufacturers’ claims for both diesel and petrol cars, meaning that motorists shouldn’t place their faith in official miles per gallon (mpg) figures.

Which? executive director, Richard Lloyd, said:
“Fuel price rises have been hitting household budgets hard, so it’s important that consumers know they are getting value for money when they buy a car.
“Diesel cars are known for their fuel efficiency, but with lower pump prices for petrol and a premium price tag for diesel cars, it may make more financial sense for families to go for the petrol version.”
The Which? study also considered reliability, taking information directly from the 2012 Which? Car Survey, which found that petrol cars are generally more reliable than diesels – both in the first three years of their life (the typical warranty period), and even more so between four and eight years-old.

Notes to editors

  1. Which? tested popular cars from superminis to estates and 4x4s, looking at identical-spec petrol and diesel versions of the Ford Fiesta, Vauxhall Astra, Volkswagen Tiguan, Volkswagen Sharan, BMW 5 Series, and Peugeot 308 SW. We calculated the annual fuel bill for each based on a mileage of 10,672 (the average annual mileage in the 2012 Which? Car Survey).
  2. In the year up to May 2012 diesel cars accounted for 51 per cent of new car sales, with petrol cars at 47.5 per cent. Alternative fuel cars accounted for 1.5 per cent.
  3. We looked at two scenarios when testing the cars: Average combined use of town, country and motorway driving; and predominantly driving around town. But for our car reviews, we test urban, extra urban, motorway (and all combined) on all the cars we test. Full details of the tests for 555 new and used models are available online at www.which.co.uk/cars

The Which? Car Survey 2012 is featured in the August edition of Which? Magazine.

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