Ford TRANSIT Owner's Manual page 109

Fuel and Refueling
Keep a record for at least one month and
record the type of driving (city or freeway).
This provides an accurate estimate of your
vehicle's fuel economy under current
driving conditions. Additionally, keeping
records during summer and winter show
how temperature impacts fuel economy.
In general, your vehicle will use more fuel
in cold temperatures.
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Transit (TTG) Vehicles Built From: 26-01-2015, CG3612en enGBR, Edition date: 12/2014, First Printing