lighter. This causes it to flow out of the top outlet
of the engine and into the top tank of the radiator.
As the coolant is cooled in the radiator, it again
becomes more dense and heavier. This causes
the coolant to settle to the bottom tank of the
The heating in the engine and the cooling in the
radiator therefore create a natural circulation that
aids the water pump.
The amount of engine heat that must be removed by
the cooling system is much greater than is generally
realized. To handle this heat load, it may be necessary
for the cooling system in some engine to circulate 4,000
to 10,000 gallons of coolant per hour. The water
passages, the size of the pump and radiator, and other
details are so designed as to maintain the working parts
of the engine at the most efficient temperature within
the limitation imposed by the coolant.
In the cooling system, the radiator is a heat
exchanger that removes the heat from the coolant
passing through it. The radiator holds a large volume of
coolant in close contact with a large volume of air so
heat will transfer from the coolant to the air. The
components of a radiator are as follows:
COREThe center section of the radiator made
up of tubes and cooling fins.
TANKSThe metal or plastic ends that fit over
core tube ends to provide storage for coolant and
fittings for the hoses.
FILLER NECKThe opening for adding
coolant. It also holds the radiator cap and
OIL COOLERThe inner tank for cooling
automatic transmission or transaxle fluid.
PETCOCKThe fitting on the bottom tank for
A tube-and-fin radiator consists of a series of tubes
extending from top to bottom or from side to side (fig.
6-5). The tubes run from the inlet tank to the outlet tank.
Fins are placed around the outside of the tubes to
improve heat transfer. Air passes between the fins. As
the air passes by, it absorbs heat from the coolant. In a
typical radiator, there are five fins per inch Radiators
used in vehicles that have air conditioning have seven
fins per inch. This design provides the additional
cooling surface required to handle the added heat load
imposed by the air conditioner.
Figure 6-5.Engine radiator construction.