One of the things that was frustrating when looking at full size vans was the lack of gas mileage information. The miles per gallon (MPG) for most vehicles are prominently displayed on the window sticker. However vans and trucks with a gross vehicle weight rating (GVWR) over 8500 lb. are exempt.
The GVWR on vans that we were considering for our travels were all above that threshold.
- Ram Promaster: 8900 lb.
- Ford Transit: 8600 lb.
- Mercedes Sprinter: 8550 lb.
- Nissan NV500: 8550 lb.
- Chevy Express: 8600 lb.
I trolled various forums searching for clues on the fuel efficiency of these vans. For the Ram Promaster I found this.
After a couple of years of travel with our Ram Promaster Sparty we have found 17 to 18 MPG is typical. This includes lots of back roads, dirt roads, some off-road and idling for air conditioning or heat. Occasionally we also run the engine to give our battery a boost if we are boondocking for a third or fourth night. There are many days that we are not fuel efficient.
I did have the opportunity to drive cross country recently to join Mrs Ram back in Massachusetts. Highway driving at normal speeds (i.e near the speed limit) I achieved 20.9 MPG. Not bad for a nearly fully load with our bikes on the back.
And as with anything posted here, your mileage may vary.