Ford 2003 Mustang Owner's Manual page 105

Using the engine block heater (if equipped)
An engine block heater warms the engine coolant,
which improves starting, warms up the engine faster
and allows the heater-defroster system to respond
quickly. Use of an engine block heater is strongly
recommended if you live in a region where
temperatures reach -23°C (-10°F) or below.
For best results, plug the heater in at least three
hours before starting the vehicle. Using the heater
for longer than three hours will not harm the engine,
so the heater can be plugged in the night before
starting the vehicle.
To prevent electrical shock, do not use your
heater with ungrounded electrical systems
or two-pronged (cheater) adapters.
Guarding against exhaust fumes
Although odorless and colorless, carbon monoxide is
present in exhaust fumes. Take precautions to avoid
its dangerous effects.
If you ever smell exhaust fumes of any kind
inside your vehicle, have your dealer inspect
and fix your vehicle immediately. Do not drive if
you smell exhaust fumes. These fumes are harmful
and could kill you.
Have the exhaust and body ventilation systems
checked whenever:
the vehicle is raised for service.
the sound of the exhaust system changes.
the vehicle has been damaged in a collision.
Starting
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