I have just bought a C3 HDi Deisel 90hp. The advertised fuel consumptions are 65mpg combined and 53mpg urban. The computer is reporting a consumption of 52mpg with urban usage. The actual consumption calculated manually us around 45mpg.
My last car was a Picasso 1.6i Petrol which was also fitted with fuel consumption computer. The reported consumption was always better than the combined advertised figure of 37mpg usually around 39-40. If driven carefully it could improve to 44mpg. I must admit I never calculated the figures manually.
Why is there a shortfall on the C3 where as the Picasso was better than the advertised figures?
Is the computer system just inherently inaccurate?
Could it be down to the way diesel and petrol engines?