I know a few people who will win their windows down on stinking hot days instead of running the A/C to save money. On of them drives an AU. In our VS Grange, the trip computer is able to display other information that doesnt usually show up unless you hold the "Set" button in while you start the engine. This then displays km/h digitally (which, for some reason is 4km/h faster than the analog speedo) and also consumption in Liters per hour (which would be a more true way of measuring how much fuel was groing through the engine at one instance. Idling, it will show about 2.2-2.5L/h I decided to do the experiment of seeing how much more using the A/C used. At the time it was displaying 2.5L/h without the A/C and 2.6L/h with it on (thats 100ml per hour more, or 8.5c) Hardly worth boiling over?