I don't think I would trust the MPG readings that the car computer gives, until I proved the readings to be correct by the miles divided by the gallons technique. It is in the manufacturers interest for the MPG reading to overstate things so you will be happy with the car. I recently saw a study where three cars by different manufacturers, were checked and all three were off, by between 1 to 3 MPG. The details of the study escape me at the moment, but maybe this explains why the new cars are said to get so much better mileage than the older cars.

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