Well I've got a belter 3.2v6 and I'll be honest, DO not expect any more than 20mpg on a flat empty motorway.
Twelve months and 4500 miles later after totting up all the fuel receipts I have averaged 17mpg.
In that twelve months I have serviced the car 3 times had the emissions checked all sweet, so as for decent fuel consumption, ha.
I love the car does everything I want and some but I think I'm going back to the dodgy diesel far better on fuel.
Hope it helps, not being negative just realistic.
