* The owner's manual: This is the most reliable source.
* The fuel filler door: The fuel tank capacity is often printed on a sticker inside the fuel filler door.
* The vehicle's sticker (monroney label): Located on the driver's side doorjamb, it might list the fuel tank capacity among other specifications.
Without knowing the specific trim level and options of the 2012 Ford E-Series Wagon, it's impossible to give a definitive answer.
