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Is your car overheating?
If you cars water bottle is
bubbling, loosing water,
steaming then you have a coolant
system problem. This can result,
if not already, in your head
gasket going
The
cooling system of a car consists of:
Water
Antifreeze
Thermostat
Cooling jacket
Water pump
Radiator and radiator cap
Expansion tank
Cooling fan
Pipes to connect it all.
WATER
Engines can be either air-cooled or water-cooled. Most
engines are water cooled because for the same volume of
water and air water can carry up to ten times more heat
away than air can.
ANTIFREEZE
Antifreeze is used to impurity the water. Impure water
has a higher boiling point so by adding antifreeze it
raises the boiling point slightly. Its other purpose is
to slow down the process of electrolysis. Some current
will flow through most cooling systems due to the fact a
car is very hard to earth, the cooling system is kept
insulated but as time goes by this isolation breaks down
and current will flow through the water by adding
antifreeze you can reduce the waters conductivity
slowing down the process. If not a badly insulated
cooling system with just water can rot the system in a
matter of 20,000 miles.
THERMOSTAT
The
thermostat is used to control the temperature of the
coolant around the engine. As the engine warms up from a
cold start the thermostat will stay closed keeping the
cold coolant in the engine. As the temperature of the
coolant increases the thermostat will open allowing the
flow of coolant to the radiator. The purpose of this is
to allow the engine to warm up quickly. If the engine is
too cool oil will remain to thick and not lubricate the
engine. Another reason to warm the coolant up quicker is
that the engines automatic choke is run from the coolant
temperature sensor. If the coolant never warms up the
choke will remain on and use more fuel. However if the
engine is run to hot the oil will be to thin and again
will not lubricate the engine. As the water gets hotter
it expands and will cause the pressure in the system to
increase and possible damage to radiators and pipes will
occur. If the temperature gets to high the aluminium
head can become twisted or warped breaking the seal
between the head gasket and block/crankcase, this result
is known as head gasket failure.
COOLING JACKET
The
cooling jacket surrounds the combustion chamber. The
cooling system works by conduction, convection, and
radiation. The cooling jacket is the first step in the
three-stage process. Conduction is the flow of heat from
a hot substance to a cool substance. The large surface
area of the cooling jacket allows for a good flow of
heat to the coolant. The cooling jacket is then the
ability to take the heat from the combustion chamber via
coolant to the radiator.
WATER PUMP
The water
pump is how the engine moves the flow of water quickly
from the engine to the radiator. The water pump is
connected to the engine via a belt or pulley. In this
way as the engine spins faster with demand the water
pump increases at the same rate to the engine. Allowing
the cooling ability at all engine spends.
RADIATOR
The
radiator is second and third step in the conduction,
convection, and radiation. The hot water flows through
the radiator through veins. These veins are covered with
smaller veins. These smaller veins increase the surface
area of the radiator. The surface area can be as much as
a small football field. These veins allow the hot water
to be cooled by the movement of air through the veins.
This is the process of radiation. The process of
convection is that cooler water is denser that hot water
which rises so the flow of water can be seen when the
hot water is cooled. This difference is why the top
radiator hose is hot and the bottom cool. The bottom
pipe is fed into the engine were as the top is fed out
of the engine.
RADIATOR CAP
The
radiator cap is a way of controlling the pressure in the
cooling system. The pressure of the cooling system is
around 15psi or 1 atmosphere. This increase in pressure
increases the boiling point of the coolant allowing the
coolant to run at a lower temperature and stopping the
boiling process of the water. If the pressure in the
system were to escape the boiling point of the water
would fall from 118oc to 100oc.
This would allow the water to boil at some of the
engines hot spots like around the exhaust ports/valves.
When the water boils it incorporates air into the system
and greatly reduces the cooling process and can burn out
the valves if they get hot enough. This localised
boiling however will not be recorded on the coolant
temperature gauge on the dash. It pays to have the cap
pressure tested every year or replaced. A faulty cap may
be spotted when a hot engine is tuned off. As the
temperature rises slightly, and hence the pressure in
the coolant system, strange gurgling noises may be heard
in the vicinity of the cap as the steam and hot air
escapes. It may not always be the radiator cap other
leaks will cause the same problem.
EXPANSION TANK
The
expansion tank allows the radiator to be filled to the
top without bursting the system. As the water heats up
it expands if the radiator was filled and sealed when
cold it would burst when it got hot. The expansion tank
allows the water to rise and fall whilst keeping the
pressure.
COOLING FAN
The fan
allows the flow of air through the radiator when the car
isn’t moving. If the car were to stay stationery it
would eventually overheat. The fans are controlled via a
relay and a temperature sensitive switch located in the
radiator. The fans come on automatically when the switch
senses the temperature rise to around 85oc.
PIPES
Pipes
are used to connect the system together. Usually
rubber pipes are used which allow them to move with
the vibration of the engine. If all metal pipes were
used they would crack rather quickly. The other
advantage of rubber hose over metal is rubber
doesn’t corrode in water like steels.
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