Ford Transit 2002 Owner's Manual page 1392

The fuel tank filler pipe incorporates a fuel tank vent pipe. The fuel tank vent pipe is
connected to the top of the fuel tank and exits just below the top of the fuel tank filler pipe.
The fuel tank vent pipe allows the displaced air above the fuel in the fuel tank to escape
without pushing the fuel entering the fuel tank during refill back up the fuel tank filler pipe.
Fuel Filler Cap
This vehicle uses a lockable fuel filler cap.
The fuel filler cap is sealed to the fuel filler neck. This is to prevent the escape of fuel vapor
during normal operation and to prevent fuel loss in the event of a vehicle accident.
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