Why your car doesn’t give the MPG you expected

VW Golf 1.6TDI is claimed to do an impressive 74.3mpg (Picture © Volkswagen)

VW Golf 1.6TDI is claimed to do an impressive 74.3mpg (Picture © Volkswagen)

Car makers along with the official fuel economy tests they all use have been blasted for showing cars to be more economical than they really are. An independent consumer organisation found this means some car firms can say their models return between 18 and 50 per cent more miles per gallon than regular buyers achieve. It would see drivers of some cars paying nearly £520 a year more than the company’s advertising led them to believe. 

The Italian consumer body Altroconsumo tested the petrol Fiat Panda 1.2 and the diesel-powered Volkswagen Golf 1.6TDI. Following its findings it is planning to go to court in Italy to help owners of these cars get some compensation.

The organisation conducted the same tests as the manufacturers in laboratory conditions but without resorting to the legitimate tricks used by the car makers. It found that the Fiat was 18 per cent less efficient than advertised while the Volkswagen used more than 50 per cent more fuel.

While VW says the Golf will do 74.3mpg, the figure Altroconsumo said it returned in the tests is 48.5mpg. If you were to do 12,000 miles a year, with diesel averaging £1.33 a litre, VW reckons you would spend £977.12 on fuel. However, if the car is 25.8mpg less economical, you would actually spend £1496.90, a difference of £519.78.

Car manufacturers’ economy figures are calculated in controlled conditions on a rolling road. The official tests have been conducted like this since the 1970s and in theory result in every car undergoing the same tests. It means cars aren’t subject to changes in gradient or wind direction, both of which can have a significant effect on fuel consumption. However, car makers also use various – currently entirely legal – tricks to improve the economy of the vehicles on the test.

By over-inflating tyres they can reduce fuel consumption by 2.9 per cent. They use special lubricants in the engines which are unavailable to normal drivers. These can dramatically improve the efficiency of their engines. They are allowed to tape up the gaps between the panels to make the car even more wind cheating and minimise the effects of air resistance.

They can remove certain fittings from the cars to lower their weight and improve economy by 4.4 per cent. They also don’t have to use functions on the car that can sap power such as air-conditioning and they are allowed to disconnect the alternator which draws power from the engine to charge the battery. The cars’ engines are also warm before part of the test so they’re running at maximum efficiency.

Monique Goyens, director general of the European consumer organisation BEUC said: “Consumers buying supposedly efficient cars are misled too often. If a car guzzles 2 litres more than advertised, consumers pay the price for what is essentially a company’s green marketing trick. Those who want to make a fuel-conscious decision when buying cars deserve accurate information.

“The deplorable side-effect of this practice is that drivers might disregard fuel consumption information altogether. Manufacturers do use tricks to make their cars look more fuel efficient. The testing system is broken and urgently needs an update. Car drivers deserve a swift EU response imposing more accurate testing.”

One comment on “Why your car doesn’t give the MPG you expected

  1. Aid Fuel Oils September 26, 2014 10:22 am

    It’s a shame that brands do this. Whether for ourselves or a business fleet, we buy because we trust what we have been told!

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