FORD 2015 E-450 - Manual (Page 99)

Using the Engine Block Heater
Make sure the receptacle terminals are clean and dry before use.
To clean them, use a dry cloth.
The heater uses 0.4 to 1.0 kilowatt-hours of energy per hour of use.
The system does not have a thermostat. It achieves maximum
temperature after approximately three hours of operation. Using the
heater longer than three hours does not improve system performance
and unnecessarily uses electricity.
98 Starting and Stopping the Engine
2015 Econoline (eco)
Owners Guide gf, 1st Printing, June 2014
USA (fus)