careless use of paint. The engine may look good but
most paints act as an insulator and hold in heat. In
addition to keeping the cooling components clean, you
must inspect them each time the engine is serviced.
Replace or repair any broken or bent parts. Check the
fins for cracks or breaks. When cracks extend into the
combustion chamber area, the cylinder barrel must be
Now that we have studied the simplest method of
cooling, lets look at the most common, but also the most
Nearly all multicylinder engines used in
automotive, construction, and material-handling
equipment use a liquid-cooled system. Any liquid used
in this type of system is called a COOLANT.
A simple liquid-cooled system consists of a
radiator, coolant pump, piping, fan, thermostat, and a
system of water jackets and passages in the cylinder
head and block through which the coolant circulates
(fig. 6-4). Some vehicles are equipped with a coolant
distribution tube inside the cooling passages that directs
additional coolant to the points where temperatures are
highest. Cooling of the engine parts is accomplished by
keeping the coolant circulating and in contact with the
metal surfaces to be cooled. The operation of a liquid-
cooled system is as follows:
The pump draws the coolant from the bottom of
the radiator, forcing the coolant through the
water jackets and passages, and ejects it into the
upper radiator tank.
The coolant then passes through a set of tubes to
the bottom of the radiator from which the cooling
The radiator is situated in front of a fan that is
driven either by the water pump or an electric
motor. The fan ensures an airflow through the
radiator at times when there is no vehicle motion.
The downward flow of coolant through the
radiator creates what is known as a thermosiphon
action. This simply means that as the coolant is
heated in the jackets of the engine, it expands. As
it expands, it becomes less dense and therefore
Figure 6-4.Liquid-cooled engine.