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Further to the information that you gave to the Mazda owner last week, I would like to add the following in your defence. The owner did not state what mileage he had covered. Generally, engines tend to "loosen up" after about 6,000 miles or so thus improving mpg attained. Motor manufacturers are governed by very strict guidelines as to how they obtain their mpg figures and for this reason, all tests are (or at least used to be) carried out on a rolling road. This, as we all know, bears no real resemblance to day to day motoring. Driving style, road conditions play a major role in this aspect, never mind the state of the vehicle itself, tyre pressures etc. Your reader would be best to ask the dealer to carry out a controlled mpg test. This involves the dealer witnessing you brimming the tank, you doing an agreed mileage and then bringing the car back with the dealer again, witnessing the car being filled back up. It is then down to simple mathematics.

Asked on 20 March 2010 by G.S., Kirkcudbright

Answered by Honest John
Unfortunately, manufacturers now flock to a certain very low resistance chassis dynamometer in Spain in perfect ambient temperatures to get their cars certificated at unrealistically low CO2 levels for tax and sales reasons. But the EC is now instituting 'in service' CO2 and fuel economy tests by which a car cannot vary by more than a few percent from its certificated figure after 100,000kms. I surmise that unless manufacturers can find another way round this, it might catch a few of them out and lead to cars being re-certificated in a different tax band with all the repercussions that will bring.
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