^^ yes I’d echo Steve’s data for the V250. Long motorway/ A roads with eco on and cruise 44MPG at least that’s what the trip meter/ data states. I also use the van albeit sparingly as a family runner/ dog walks for some smaller more start stop journeys it’s a good bit less, mid 30’s. I will pay some attention to those journeys and report back in time.
I do a long run up the M6 regularly and notice a big difference in winter/summer mpg but driving style the same. About 44 in summer and can be 38 ish in winter, assume its the temperature/wind plus usually on wet roads with lights on, fan running etc.
There is a big difference between 50 - 60 mph and 70 mph. I drive regularly through the M6 roadworks above the M62 interchange and its approx 15 miles & 50mph, on a long motorway run it pushes up the overall mpg by 2-3.
I suspect the MPG value displayed on the instruments is optimistic. For me it often reads about 46 to 50 mpg, but generally turns out to be about 42 mpg when calculated at the pump (mileage divided by litres added to full) following long runs. I log my mileage on the spritmonitor app which suggests across 69 Marco Polos fuel consumption on average is about 33 mpg: Consumption: Mercedes-Benz - V-Klasse - Spritmonitor.de . This compares with 30.5 mpg average for a VW California Consumption: Volkswagen - Transporter - Spritmonitor.de - 70 vehicles. I suspect the more recent 9 speed Marco Polos might offer better fuel consumption on a long run based on official WLTP figures. If you use the diesel heater then it will confuse the tank based mpg calculations!
optimistic - possibly - but then at least bad MPG reading for a blast through town would also be equally erroneous - I planned to score every diesel purchase/milage in a note book i put in the centre console - did it only once... I cant see how topping up and clocking milage is any less prone to error.. personally I feel removing humans from the equation is without doubt going to render more reliable results optimistic or not.. My previous car was a W638 V-Class 2.8L V6 that probably did 17mpg on a good day so to be completely honest anything over 25mpg is a dream..