>This assumes no fast acceleration hard braking and keeping under 80 mph.
>I was impressed with the large Mercedes saloon that uses a 1.3 engine and has 160 bhp on tap and do 50 mpg in petrol form. Unfortunately, if you run this at 90 mph it will lower to 35mpg if lucky.
Just as a matter of possible interest:-
. When I met swmbo in 1999, she was running a '92 1.9 diesel Citroen ZX - 55 mpg usually, 50 mpg if really thraped on the motorway for a long distance. Excellent aerodynamics, almost completely unaffected by sidewinds.
. One of the current cars is an 11-year-old Audi A3 1.9 diesel, consistently a little over 50 mpg whether trundling around the Highlands up to around 60 mph or on a long journey including motorways. Will fall to a little under 50 mpg in the winter because swmbo leaves it idling to warm up inside in the morning.
. Last of series of Mercs was a 2.7-litre C-class estate. Would give high-40's mpg on a run even sur le Continong fully-loaded ... and diesel was cheaper than petrol. Only reason I didn't keep it up here was its RWD needed four winter tyres whereas FWD gets away with two.
. Two recent Mazda 5 7-seaters - 2006 petrol gave low-30's mpg, 2008 diesel gave mid-40's mpg - same 2-litre engine size, same mix of driving conditions, the diesel was even the 147 bhp 'Sport' version. Only problem with diesel Mazdas is their shonky DPF cleaning.
. The Merc would do Highlands to SE England comfortably on one tankful with some left over, the other diesels have 60-litre tanks and, for peace-of-mind, need one fuel stop. Given one of those plus a pee can be under ten minutes, makes the current electric claims of 200 miles on one charge look about as much use as a chocolate teapot.