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The Components of a Cooling System are:
The Radiator
The radiator core is usually made of flattened
aluminum tubes with aluminum strips that zigzag
between the tubes. These fins transfer the heat in
the tubes into the air stream to be carried away
from the vehicle. On each end of the radiator core
is a tank, usually made of plastic that covers the
ends of the radiator,
On most modern radiators, the tubes run horizontally
with the plastic tank on either side. On other cars,
the tubes run vertically with the tank on the top
and bottom. On older vehicles, the core was made of
copper and the tanks were brass. The new
aluminum-plastic system is much more efficient, not
to mention cheaper to produce. On radiators with
plastic end caps, there are gaskets between the
aluminum core and the plastic tanks to seal the
system and keep the fluid from leaking out. On older
copper and brass radiators, the tanks were brazed (a
form of welding) in order to seal the radiator.
The
tanks, whether plastic or brass, each have a large
hose connection, one mounted towards the top of the
radiator to let the coolant in, the other mounted at
the bottom of the radiator on the other tank to let
the coolant back out. On the top of the radiator is
an additional opening that is capped off by the
radiator cap. More on this later.
Another component in the radiator for vehicles with
an automatic transmission is a separate tank mounted
inside one of the tanks. Fittings connect this inner
tank through steel tubes to the automatic
transmission. Transmission fluid is piped through
this tank inside a tank to be cooled by the coolant
flowing past it before returning the the
transmission.
Radiator Fans
Mounted on the back of the radiator on the side
closest to the engine is one or two electric fans
inside a housing that is designed to protect fingers
and to direct the air flow. These fans are there to
keep the air flow going through the radiator while
the vehicle is going slow or is stopped with the
engine running. If these fans stopped working, every
time you came to a stop, the engine temperature
would begin rising. On older systems, the fan was
connected to the front of the water pump and would
spin whenever the engine was running because it was
driven by a fan belt instead of an electric motor.
In these cases, if a driver would notice the engine
begin to run hot in stop and go driving, the driver
might put the car in neutral and rev the engine to
turn the fan faster which helped cool the engine.
Racing the engine on a car with a malfunctioning
electric fan would only make things worse because
you are producing more heat in the radiator with no
fan to cool it off.
The electric fans are controlled by the vehicle's
computer. A temperature sensor monitors engine
temperature and sends this information to the
computer. The computer determines if the fan should
be turned on and actuates the fan relay if
additional air flow through the radiator is
necessary.
If the car has air conditioning, there is an
additional radiator mounted in front of the normal
radiator. This "radiator" is called the air
conditioner condenser, which also needs to be cooled
by the air flow entering the engine compartment. You
can find out more about the air conditioning
condenser by going to our article on Automotive Air
Conditioning. As long as the air conditioning is
turned on, the system will keep the fan running,
even if the engine is not running hot. This is
because if there is no air flow through the air
conditioning condenser, the air conditioner will not
be able to cool the air entering the interior.
Pressure
cap and reserve tank
As coolant gets hot, it expands. Since the cooling
system is sealed, this expansion causes an increase
in pressure in the cooling system, which is normal
and part of the design. When coolant is under
pressure, the temperature where the liquid begins to
boil is considerably higher. This pressure, coupled
with the higher boiling point of ethylene glycol,
allows the coolant to safely reach temperatures in
excess of 250 degrees.
The radiator pressure cap is a simple device that
will maintain pressure in the cooling system up to a
certain point. If the pressure builds up higher than
the set pressure point, there is a spring loaded
valve, calibrated to the correct Pounds per Square
Inch (psi), to release the pressure.
When the cooling system pressure reaches the point
where the cap needs to release this excess pressure,
a small amount of coolant is bled off. It could
happen during stop and go traffic on an extremely
hot day, or if the cooling system is malfunctioning.
If it does release pressure under these conditions,
there is a system in place to capture the released
coolant and store it in a plastic tank that is
usually not pressurized. Since there is now less
coolant in the system, as the engine cools down a
partial vacuum is formed. The radiator cap on these
closed systems has a secondary valve to allow the
vacuum in the cooling system to draw the coolant
back into the radiator from the reserve tank (like
pulling the plunger back on a hypodermic needle)
There are usually markings on the side of the
plastic tank marked Full-Cold, and Full Hot. When
the engine is at normal operating temperature, the
coolant in the translucent reserve tank should be up
to the Full-Hot line. After the engine has been
sitting for several hours and is cold to the touch,
the coolant should be at the Full-Cold line.
Water Pump
A water
pump is a simple device that will keep the coolant
moving as long as the engine is running. It is
usually mounted on the front of the engine and turns
whenever the engine is running. The water pump is
driven by the engine through one of the following:
-
A fan
belt that will also be responsible for driving
an additional component like an alternator or
power steering pump
-
A
serpentine belt, which also drives the
alternator, power steering pump and AC
compressor among other things.
-
The
timing belt that is also responsible for driving
one or more camshafts.
The water
pump is made up of a housing, usually made of cast
iron or cast aluminum and an impeller mounted on a
spinning shaft with a pulley attached to the shaft
on the outside of the pump body. A seal keeps fluid
from leaking out of the pump housing past the
spinning shaft. The impeller uses centrifugal force
to draw the coolant in from the lower radiator hose
and send it under pressure into the engine block.
There is a gasket to seal the water pump to the
engine block and prevent the flowing coolant from
leaking out where the pump is attached to the block.
Thermostat
 The thermostat is simply a valve that measures the
temperature of the coolant and, if it is hot enough,
opens to allow the coolant to flow through the
radiator. If the coolant is not hot enough, the flow
to the radiator is blocked and fluid is directed to
a bypass system that allows the coolant to return
directly back to the engine. The bypass system
allows the coolant to keep moving through the engine
to balance the temperature and avoid hot spots.
Because flow to the radiator is blocked, the engine
will reach operating temperature sooner and, on a
cold day, will allow the heater to begin supplying
hot air to the interior more quickly.
Since the 1970s, thermostats have been calibrated to
keep the temperature of the coolant above 192 to 195
degrees. Prior to that, 180 degree thermostats were
the norm. It was found that if the engine is allowed
to run at these hotter temperatures, emissions are
reduced, moisture condensation inside the engine is
quickly burned off extending engine life, and
combustion is more complete which improves fuel
economy.
The heart of a thermostat is a sealed copper cup
that contains wax and a metal pellet. As the
thermostat heats up, the hot wax expands, pushing a
piston against spring pressure to open the valve and
allow coolant to circulate.
The thermostat is usually located in the front, top
part of the engine in a water outlet housing that
also serves as the connection point for the upper
radiator hose. The thermostat housing attaches to
the engine, usually with two bolts and a gasket to
seal it against leaks. The gasket is usually made of
a heavy paper or a rubber O ring is used. In some
applications, there is no gasket or rubber seal.
Instead, a thin bead of special silicone sealer is
squeezed from a tube to form a seal.
There is a mistaken belief by some people that if
they remove the thermostat, they will be able to
solve hard to find overheating problems. This
couldn't be further from the truth. Removing the
thermostat will allow uncontrolled circulation of
the coolant throughout the system. It is possible
for the coolant to move so fast, that it will not be
properly cooled as it races through the radiator, so
the engine can run even hotter than before under
certain conditions. Other times, the engine will
never reach its operating temperature. On computer
controlled vehicles, the computer monitors engine
temperatures and regulates fuel usage based on that
temperature. If the engine never reaches operating
temperatures, fuel economy and performance will
suffer considerably.
Bypass System
This is a passage that allows the coolant to bypass
the radiator and return directly back to the engine.
Some engines use a rubber hose, or a fixed steel
tube. In other engines, there is a cast in passage
built into the water pump or front housing. In any
case, when the thermostat is closed, coolant is
directed to this bypass and channeled back to the
water pump, which sends the coolant back into the
engine without being cooled by the radiator.
Freeze Plugs
When an engine block is manufactured, a special sand
is molded to the shape of the coolant passages in
the engine block. This sand sculpture is positioned
inside a mold and molten iron or aluminum is poured
to form the engine block. When the casting is
cooled, the sand is loosened and removed through
holes in the engine block casting leaving the
passages that the coolant flows through. Obviously,
if we don't plug up these holes, the coolant will
pour right out.
Plugging these holes is the job of the freeze-out
plug. These plugs are steel discs or cups that are
press fit in the holes in the side of the engine
block and normally last the life of the engine with
no problems. But there is a reason they are called
freeze-out plugs. In the early days, many people
used plain water in their engines, usually after
replacing a burst hose or other cooling system
repair. "It is summer and I will replace the water
with antifreeze when the weather starts turning".
Needless to say, people are forgetful and many a
motor suffered the fate of the water freezing inside
the block. Often, when this happened the pressure of
the water freezing and expanding forced the
freeze-out plugs to pop out, relieving the pressure
and saving the engine block from cracking.
(although, just as often the engine cracked anyway).
Another reason for these plugs to fail was the fact
that they were made of steel and would easily rust
through if the vehicle owner was careless about
maintaining the cooling system. Antifreeze has rust
inhibitors in the formula to prevent this from
happening, but those chemicals would lose their
effect after 3 years, which is why antifreeze needs
to be changed periodically. The fact that some
people left plain water in their engines greatly
accelerated the rusting of these freeze plugs.
When a freeze plug becomes so rusty that it
perforates, you have a coolant leak that must be
repaired by replacing the rusted out freeze plug
with a new one. This job ranges from fairly easy to
extremely difficult depending on the location of the
affected freeze plug. Freeze plugs are located on
the sides of the engine, usually 3 or 4 per side.
There are also freeze plugs on the back of the
engine on some models and also on the heads.
As long as you are good about maintaining the
cooling system, you need never worry about these
plugs failing on modern vehicles
Head Gaskets and Intake Manifold Gaskets
All internal combustion engines have an engine block
and one or two cylinder heads. The mating surfaces
where the block and head meet are machined flat for
a close, precision fit, but no amount of careful
machining will allow them to be completely water
tight or be able to hold back combustion gases from
escaping past the mating surfaces.
In order to seal the block to the heads, we use a
head gasket. The head gasket has several things it
needs to seal against. The main thing is the
combustion pressure on each cylinder. Oil and
coolant must easily flow between block and head and
it is the job of the head gasket to keep these
fluids from leaking out or into the combustion
chamber, or each other for that matter.
A typical head gasket is usually made of soft sheet
metal that is stamped with ridges that surround all
leak points. When the head is placed on the block,
the head gasket is sandwiched between them. Many
bolts, called head bolts are screwed in and
tightened down causing the head gasket to crush and
form a tight seal between the block and head.
Head gaskets usually fail if the engine overheats
for a sustained period of time causing the cylinder
head to warp and release pressure on the head
gasket. This is most common on engines with cast
aluminum heads, which are now on just about all
modern engines.
Once coolant or combustion gases leak past the head
gasket, the gasket material is usually damaged to a
point where it will no longer hold the seal. This
causes leaks in several possible areas. For example:
combustion gases could leak into the coolant
passages causing excessive pressure in the cooling
system.
coolant could leak into the combustion chamber
causing coolant to escape through the exhaust
system, often causing a white cloud of smoke at the
tailpipe.
Other problems such as oil mixing with the coolant
or being burned out the exhaust are also possible.
Some engines are more susceptible to head gasket
failure than others. I have seen blown head gaskets
on engines that just started to overheat and were
running hot for less than 5 minutes. The best advice
I can give is, if the engine shows signs of
overheating, find a place to pull over and shut the
engine off as quickly as possible.
Head gaskets themselves are relatively cheap, but it
is the labor that's the killer. A typical head
gasket replacement is a several hour job where the
top part of the engine must be completely
disassembled. These jobs can easily reach ,000 or
more.
On V type engines, there are two heads, meaning two
head gaskets. While the labor won't double if both
head gaskets need to be replaced, it will probably
add a good 30% more labor to replace both. If only
one head gasket has failed, it is usually not
necessary to replace both, but it could be added
insurance to get them both done at once.
A head gasket replacement begins with the diagnosis
that the head gasket has failed. There is no way for
a technician to know for certain whether there is
additional damage to the cylinder head or other
components without first disassembling the engine.
All he or she knows is that fluid and/or combustion
is not being contained.
One way to tell if a head gasket has failed is
through a combustion leak test on the radiator. This
is a chemical test that determines if there are
combustion gases in the engine coolant. Another way
is to remove the spark plugs and crank the engine
while watching for water spray from one or more
spark plug holes. Once the technician has determined
that a head gasket must be replaced, an estimate is
given for parts and labor. The technician will then
explain that there may be additional charges after
the engine is opened if more damage is found.
Heater Core
The hot coolant is also used to provide heat to the
interior of the vehicle when needed. This is a
simple and straight forward system that includes a
heater core, which looks like a small version of a
radiator, connected to the cooling system with a
pair of rubber hoses. One hose brings hot coolant
from the water pump to the
 heater core and the other
hose returns the coolant to the top of the engine.
There is usually a heater control valve in one of
the hoses to block the flow of coolant into the
heater core when maximum air conditioning is called
for.
A fan, called a blower, draws air through the heater
core and directs it through the heater ducts to the
interior of the car. Temperature of the heat is
regulated by a blend door that mixes cool outside
air, or sometimes air conditioned air with the
heated air coming through the heater core. This
blend door allows you to control the temperature of
the air coming into the interior. Other doors allow
you to direct the warm air through the ducts on the
floor, the defroster ducts at the base of the
windshield, and the air conditioning ducts located
in the instrument panel.
Hoses
There are several rubber hoses that make up the
plumbing to connect the components of the cooling
system. The main hoses are called the upper and
lower radiator hoses. These two hoses are
approximately 2 inches in diameter and direct
coolant between the engine and the radiator. Two
additional hoses, called heater hoses, supply hot
coolant from the engine to the heater core. These
hoses are approximately 1 inch in diameter. One of
these hoses may have a heater control valve mounted
in-line to block the hot coolant from entering the
heater core when the air conditioner is set to
max-cool. A fifth hose, called the bypass hose, is
used to circulate the coolant through the engine,
bypassing the radiator, when the thermostat is
closed. Some engines do not use a rubber hose.
Instead, they might use a metal tube or have a
built-in passage in the front housing.
These hoses are designed to withstand the pressure
inside the cooling system. Because of this, they are
subject to wear and tear and eventually may require
replacing as part of routine maintenance. If the
rubber is beginning to look dry and cracked, or
becomes soft and spongy, or you notice some
ballooning at the ends, it is time to replace them.
The main radiator hoses are usually molded to a
shape that is designed to rout the hose around
obstacles without kinking. When purchasing
replacements, make sure that they are designed to
fit the vehicle.
There is a small rubber hose that runs from the
radiator neck to the reserve bottle. This allows
coolant that is released by the pressure cap to be
sent to the reserve tank. This rubber hose is about
a quarter inch in diameter and is normally not part
of the pressurized system. Once the engine is cool,
the coolant is drawn back to the radiator by the
same hose.
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