Spa trip 41 mpg! :-)

[awolfinsheepsclothes]

But is it simple?
Has a D2 got a speed it's happy cruse at in sensible speed on the motorway between 50-90 where it doesn't cost the earth.
Fuel economy at steady speeds with selected vehicles was studied in 2010. The most recent study indicates greater fuel efficiency at higher speeds than earlier studies; for example, some vehicles achieve better mileage at 65 mph (105 km/h) rather than at 45 mph (72 km/h), although not their best economy, such as the 1994 Oldsmobile Cutlass, which has its best economy at 55 miles per hour (89 km/h) (29.1 mpg-US (8.08 L/100 km)), and gets 2 mpg better economy at 65 mph (105 km/h) than at 45 mph (72 km/h) (25 mpg-US (9.4 L/100 km) vs 23 mpg-US (10 L/100 km)). The proportion of driving on high speed roadways varies from 4% in Ireland to 41% in Netherlands.
When the National Maximum Speed Law's 55 mph (89 km/h) speed limit was mandated, there were complaints that fuel economy could decrease instead of increase. The 1997 Toyota Celica got 1 mpg better fuel-efficiency at 65 mph (105 km/h) than it did at 45 mph (72 km/h) (43.5 mpg-US (5.41 L/100 km) vs 42.5 mpg-US (5.53 L/100 km)), although almost 5 mpg better at 60 mph (97 km/h) than at 65 mph (105 km/h) (48.4 mpg-US (4.86 L/100 km) vs 43.5 mpg-US (5.41 L/100 km)), and its best economy (52.6 mpg-US (4.47 L/100 km)) at only 25 mph (40 km/h). Other vehicles tested had from 1.4 to 20.2% better fuel-efficiency at 55 mph (89 km/h) vs. 65 mph (105 km/h). Their best economy was reached at speeds of 25 to 55 mph (40 to 89 km/h)
Officials hoped that the 55 mph limit, This was partly based on a belief that cars achieve maximum efficiency between 40 and 50 mph (64 and 80 km/h) and that trucks and buses were most efficient at 55 mph (89 km/h).