* The owner's manual: This is the most reliable source.
* The fuel filler door: The fuel tank capacity is sometimes printed on a sticker on the inside of the fuel filler door.
* The vehicle's sticker: A sticker with vehicle information (including fuel tank capacity) might be located on the driver's side doorjamb or elsewhere inside the vehicle.
Without knowing the specific trim and configuration of the van, it's impossible to give you a precise fuel tank capacity.