Figure 6-1.Air-cooled system.
types, and the discussion will include a description of
the various components of the systems and an
explanation of their operation.
The simplest type of cooling is the air-cooled, or
direct, method in which the heat is drawn off by moving
air in direct contact with the engine (fig. 6-1). Several
fundamental principles of cooling are embodied in this
type of engine cooling.
The rate of the cooling is
dependent upon the following:
Some heat, of course, must be retained for efficient
The difference in temperature between the
exposed metal surfaces and the cooling air
The area exposed to the cooling medium
The heat conductivity of the metal used & the
volume of the metal or its size in cross section
The amount of air flowing over the heated
operation. This is done by use of thermostatic controls
and mechanical linkage, which open and close shutters
to control the volume of cooling air. You will find that
air-cooled engines generally operate at a higher
temperature than liquid-cooled engines whose
operating temperature is largely limited by the boiling
point of the coolant used. Consequently greater
clearances must be provided between the moving parts
of air-cooled engines to allow for increased expansion.
Also, lubricating oil of a higher viscosity is generally
Figure 6-2.Air-cooled cylinder.