Ford 1996 Aerostar Manual page 250

Cleaning the Engine
A clean engine is more efficient because a
buildup of grease and dirt acts as an insulator,
keeping the engine warmer than usual.
Extreme care must be used if a power washer
is used to clean the engine. The high pressure
fluid could penetrate sealed parts and
assemblies causing damage or malfunctions.
In order to avoid possible cracking of the
engine block, do not spray a hot engine with
cold water.
The alternator and air intake must be
covered. Covering these components will help
prevent water damage.
Never wash or rinse the engine while it is
running. Water getting into the engine may
cause internal damage.
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