I got around 5-7 MPG in the winter with my 1980 Chrysler Cordoba with a 318ci V8 back when I was in the 12th grade.
I would start up the car in the morning, let it idle for about 20 minutes and then drive 4.6 kilometres to high-school
.
When I first bought it (in summer 2002), I filled the tank with $5 after 50 kilometres. I remember the gas mileage of that tank being just above 20 mpg(IMP) for all city driving; about 16.5 mpg(US).