A radiator is a
type of heat exchanger. It is designed to transfer heat from
the hot coolant that flows through it to the air blown
through it by the fan.
Most modern cars use aluminum radiators.
These radiators are made by brazing thin aluminum fins to
flattened aluminum tubes. The coolant flows from the inlet
to the outlet through many tubes mounted in a parallel
arrangement. The fins conduct the heat from the tubes and
transfer it to the air flowing through the radiator.
The tubes sometimes have a type of fin inserted into them called a
turbulator, which increases the turbulence of the fluid
flowing through the tubes. If the fluid flowed very smoothly
through the tubes, only the fluid actually touching the
tubes would be cooled directly. The amount of heat
transferred to the tubes from the fluid running through them
depends on the difference in temperature between the tube
and the fluid touching it. So if the fluid that is in
contact with the tube cools down quickly, less heat will be
transferred. By creating turbulence inside the tube, all of
the fluid mixes together, keeping the temperature of the
fluid touching the tubes up so that more heat can be
extracted, and all of the fluid inside the tube is used
Picture of radiator showing side tank with cooler.
usually have a tank on each side, and inside tank is a
transmission cooler. In the picture above, you can see the
inlet and outlet where the oil from the transmission enters
the cooler. The transmission cooler is like a radiator
within a radiator, except instead of exchanging heat with
the air, the oil exchanges heat with the coolant in the
The radiator cap actually increases
the boiling point of your coolant by about 45░
F (25░ C). How does this simple cap do
this? The same way a pressure cooker increases the boiling temperature of water.
The cap is actually a pressure release valve, and on cars it is usually set to
The boiling point of water
increases when the water is placed under pressure.
Cutaway of radiator cap
When the fluid
in the cooling system heats up, it expands, causing the
pressure to build up. The cap is the only place where this
pressure can escape, so the setting of the spring on the cap
determines the maximum pressure in the cooling system. When
the pressure reaches 15 psi, the pressure pushes the valve
open, allowing coolant to escape from the cooling system.
This coolant flows through the overflow tube into the bottom
of the overflow tank. This arrangement keeps air out of the
system. When the radiator cools back down, a vacuum is
created in the cooling system that pulls open another spring
loaded valve, sucking water back in from the bottom of the
overflow tank to replace the water that was expelled.