FORD 2013 E-450 v.3 - Manual (Page 210)

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]).
Maintenance 209
2013 Econoline (eco)
Owners Guide gf, 3rd Printing, May 2013
USA (fus)