So Ive been thinking about how much petrol my station wagon drinks. About 13.5L/100km or down in the 12's with ultra careful straight driving. It seems like a lot to me, but then again its speedo is very accurate against a GPS, so am I right in thinking that the distance meter also works off the same signal? On the other hand my blackbirds speedo is optimistic, by about 7%, so going off its distance meter, its fuel econ is probably worse - around 7L/100km rather than the 6-6.5 Im currently calculating. So I know my old tank of a car is not efficient, but just how bad is it compared to modern cars when you factor in the speedo? Ive driven foresters and outlanders and they return 9-9.5L/100km but I am thinking its closer to 10-10.5 Any input? Any owners of newish commodores or falcons?