combustion passes by conduction from the cylinder
vehicles, airflow is provided both by the fan and the
walls and cylinder head to the fins, and is carried away
forward motion of the vehicle.
by the passing air.
From the bottom of the radiator, the coolant flows
through a lower hose connection to the pump where it
Maintaining the Air-Cooled System
is again forced into the cylinder block and repeats the
cooling cycle, thus removing more heat from the
You may feel that because the air-cooling system is
engine and carrying the heat into the radiator.
so simple it requires no maintenance. Too many
mechanics feel this way; many air-cooled engine
The amount of engine heat that must be removed
failures occur as a result. Maintenance of an
by the cooling system is much greater than is generally
air-cooling system consists primarily of keeping
realized. To handle this heat load, it may be necessary
cooling components clean. Clean components permit
for the cooling system in some engines to circulate
rapid transfer of heat and ensure that nothing prevents
4,000 to 10,000 gallons of coolant per hour. The water
the continuous flow and circulation of air. To
passages, the size of the pump and radiator, and other
accomplish this, keep fans, shrouds, baffles, and fins
details are so designed as to maintain the working parts
free of dirt, bugs, grease, and other foreign matter. The
of the engine at the most efficient temperature within
engine may look clean from the outside, but what is
the limitations imposed by the coolant. Figure 5-2
under the shroud? Accumulation of dirt and debris
shows a typical liquid-cooling system and most of its
here can cause real problems.
components.
Keep the area between the engine and shroud
clean. Paint can cause a problem. Sometimes a
Radiator
mechanic will reduce the efficiency of the cooling
system by careless use of paint. The engine may look
The radiator is probably the key unit in a
good, but most paints act as an insulator and hold in
liquid-cooled system. It is a device for holding a
heat. In addition to keeping the cooling components
considerable volume of coolant in close contact with a
clean, you should inspect them each time the engine is
large volume of air so that heat may be transferred from
serviced. Replace or repair any broken or bent parts.
the coolant to the air.
Check the fins for cracks or breaks. When cracks
The usual radiator assembly consists of a radiator
extend into the combustion chamber area, the cylinder
core with a top tank and a bottom tank. The top, or inlet
barrel must be replaced.
tank, has an outside pipe called the "radiator inlet," and
LIQUID-COOLING SYSTEMS
it usually has a coolant baffle inside and above or at the
inlet opening. The radiator filler neck is generally
Nearly a l l m u l t i c y l i n d e r e n g i n e s u s e d i n
attached to the upper part of the top tank and has an
automotive, construction, and material-handling
outlet to the overflow pipe. The bottom tank also has a
equipment use a liquid-cooling system. Any liquid
pipe that is the radiator outlet. Many radiators for
used in this type of system is called a "coolant."
vehicles equipped with automatic transmissions have
an inner core located in the bottom tank through which
In most liquid-cooled engines, excess heat is
removed by the circulation of the coolant through
transmission oil is circulated to assist cooling of the
hollow passages surrounding the hottest parts of the
transmission.
engine. Heat flows first into the coolant while the
Practically all cooling systems have tubular
coolant is being pumped through the passages of the
radiator cores (fig. 5-3), which consist of a large
cylinder block and up into the cylinder head. The
number of vertical tubes and many horizontal air fins
coolant then moves on through similar passages in the
around the tubes. Water passages in the tubes are
head, picks up more heat as it circulates, and finally
usually quite narrow, and the tube itself is made of thin
leaves the engine through an outlet at the top.
metal.
After leaving the engine, the coolant passes
Through the water tubes, the flow of coolant is
through an upper hose connection and carries the heat
divided into many small streams, which cause a small
into a radiator. As the coolant flows down through the
amount of cooling liquid to be exposed to a
radiator, a stream of air forced through the radiator
comparatively large cooling surface. This results in
removes the heat. In stationary engines, the fan
rapid flow of heat from the coolant to the tubes and air
provides all of the airflow. For engines installed in
5-3
