Block Heater Information

Don't hesitate to plug in the block heater on your truck. The fact that it hasn't been used isn't an issue. Most 'block' heaters consist of small electrical heating elements mounted into a replacement 'frost plug' installed on the engine block. The heating element reaches into the cooling jacket surrounding the cylinders so that it is directly immersed in the coolant full-time, whether the unit is ever plugged in or not. So, since you've kept up with routine cooling system service, there should be no significant sediment in the system anyway.
Unless temperatures drop to 30 or 40 below zero, set up an outlet timer to turn on the block heater two to four hours before you need to start the vehicle. That's enough time to warm the coolant sufficiently to assist the engine in cranking and starting. By the way, a key benefit of warming the coolant is to warm the cylinder walls to reduce the percentage of incoming fuel that condenses on the cold metal and contributes to non-start/flooded engines