Radiators are classified according to the direction
that the coolant flows through them. The two types of
radiators are the downflow and crossflow.
The downflow radiator has the coolant tanks on
the top and bottom and the core tubes run
vertically. Hot coolant from the engine enters the
top tank. The coolant flows downward through
the core tubes. After cooling, coolant flows out
the bottom tank and back into the engine.
The crossflow radiator is a design that has the
tanks on the sides of the core. The core tubes are
arranged for horizontal coolant flow. The tank
with the radiator cap is normally the outer tank.
A crossflow radiator can be shorter, allowing for
a lower vehicle hood.
The operation of a radiator is as follows:
The upper tank collects incoming coolant and,
through the use of an internal baffle, distributes it
across the top of the core.
The core is made up of numerous rows of small
vertical tubes that connect the upper tank and the
lower tank. Sandwiched between the rows of
tubes are thin sheet metal fins. As the coolant
passes through the tubes to the lower tank, the
fins conduct the heat away from it and dissipate
this heat into the atmosphere. The dissipation of
the heat from the fins is aided by directing a
constant air flow between the tube and over the
The lower tank collects the coolant from the core
and discharges it to the engine through the outlet
The overflow tube provides an opening from the
radiator for escape of coolant if the pressure in
the system exceeds the regulated maximum.
This will prevent rupture of cooling system
A transmission oil cooler is often placed in the
radiator on vehicles with automatic transmissions. It is
a small tank enclosed in one of the main radiator tanks.
Since the transmission fluid is hotter than engine
coolant, heat is removed from the fluid as it passes
through the radiator and cooler.
In downflow radiators, the transmission oil cooler
is located in the lower tank. In a crossflow radiator, it is
located in the tank having the radiator cap. Both tanks
are coolant outlet tanks.
Line fittings from the cooler extend through the
radiator tank to the outside. Metal lines from the
automatic transmission connect to these fittings. The
transmission oil pump forces the fluid through the lines
Radiator hoses carry coolant between the engine
water jackets and the radiator. Being flexible, hoses can
withstand the vibration and rocking of the engine
The upper radiator hose normally connects to the
thermostat housing on the intake manifold or cylinder
head. The other end of the hose fits on the radiator. The
lower hose connects the water pump inlet and the
A molded hose is manufactured into a special shape
with bends to clean the parts especially the cooling fan.
It must be purchased to fit the exact year and make of the
A flexible hose has an accordion shape and can be
bent to different angles.
The pleated construction
allows the hose to bend without collapsing and blocking
coolant flow. It is also known as a universal type
A hose spring is used in the lower radiator hose to
prevent its collapse.
The lower hose is exposed to
suction from the water pump. The spring assures that
the inner lining of the hose does NOT tear away, close
up, and stop circulation.
Radiator Pressure Cap
The radiator pressure cap (fig. 6-6) is used on nearly
all of the modern engines. The radiator cap locks onto
the radiator tank filler neck Rubber or metal seals make
the cap-to-neck joint airtight. The functions of the
pressure cap are as follows:
1. Seals the top of the radiator tiller neck to prevent
2. Pressurizes system to raise boiling point of
3. Relieves excess pressure to protect against
4. In a closed system, it allows coolant flow into
and from the coolant reservoir.
The radiator cap pressure valve consists of a spring-
loaded disc that contacts the filler neck. The spring
pushes the valve into the neck to form a seal. Under