Ford Econoline E-150 Owner's Manual page 216

Maintenance 215
Correct Fluid Level
The transmission fluid should be checked at normal operating
temperature 150°F-170°F (66°C-77°C) on a level surface. The normal
operating temperature can be reached after approximately 20 miles
(30 km) of driving.
You can check the fluid without driving if the ambient temperature is above
50°F (10°C). However, if fluid is added at this time, an overfill condition
could result when the vehicle reaches normal operating temperature.
The transmission fluid should be in this range if at normal operating
temperature (150°F-170°F [66°C-77°C]).
2013 Econoline (eco)
Owners Guide gf, 2nd Printing, November 2012
USA (fus)