Ford Mustang Owner's Manual page 153

Do not park, idle, or drive your vehicle in
dry grass or other dry ground cover. The
emission system heats up the engine
compartment and exhaust system, which
can start a fire.
If you consistently start your vehicle in subzero
temperatures, use an engine block heater (if
your vehicle has this option).
Engine Block Heater (If equipped)
Engine block heaters are strongly recommended
if you live in a region where temperatures reach
-10˚F (-23˚C) or below. An engine block heater
warms the engine coolant, which improves
starting, warms up the engine faster, and allows
the heater-defrost system to respond quickly.
To turn the heater on, simply plug it into a
grounded 110-volt outlet. Ford recommends that
you use a 110-volt circuit that is protected by a
ground fault circuit interrupter.
To prevent electrical shock, do not use
your heater with ungrounded electrical
systems or two-pronged (cheater) adapters.
For best results, plug the heater in at least three
hours before you start your vehicle. Using the
heater for longer than three hours will not
damage the engine, so you can plug it in at
night to start your vehicle the following
morning.
NOTE: Be sure to disconnect the engine block
heater before driving your vehicle.
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