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The radiator is a device designed to dissipate the heat which the
coolant has absorbed from the engine. It is constructed to hold a large
amount of water in tubes or passages which provide a large area in
contact with the atmosphere. It consists of a radiator core, which has
water-carrying tubes and a large cooling area, which are connected to a
receiving tank (end cap) at the top and to a dispensing tank at the
bottom. Cross flow radiators have their "end caps" on the
sides, which allows a lower hood line.
In operation, water is pumped from the engine to the top (receiving)
tank, where it spreads over the tops of the tubes. As the water passes
down through the tubes, it loses it's heat to the air stream which passes
around the outside of the tubes.
Sooner or later, almost everyone has to deal with an overheating car.
Since water is readily available, it is not beyond the ability of most
people to add some to their radiator if it is low. . Here
are a few pointers for dealing with an overheated radiator:
- Turn off the A/C. If the car is not seriously overheating, this
will reduce the engine's temperature.
- Turn ON your heater (set on highest temperature setting, with the
blower on it's highest setting). This will not be comfortable
(especially on a 90 degree day) but it will cool the engine by
transferring the heat to the air.
- If you're stuck in traffic, pull over and stop. Unless you're
moving, very little cool air reaches the radiator. Open the hood and
let the engine cool off. This takes time, (45 minutes to an hour) so
be very patient. Use this time to get a container of water or
antifreeze.
- Check the overflow tank coolant level. If it is empty, the
radiator is probably low on coolant.
- Place a large cloth over the radiator cap, and when cooled off,
CAREFULLY release the pressure. .
- If the coolant is low, start the engine, and slowly add water or
coolant necessary to fill it up. THE ENGINE MUST BE RUNNING.
ADDING COOLANT TO A WARM ENGINE CAN CRACK THE BLOCK. By
running the engine, the coolant keeps moving and reduces the chances
of this type of damage.
Water pumps come in many designs, but all work the same. They use a
rotating impeller to force the coolant through the engine block.
Impeller type water pumps must turn rapidly to be efficient, and worn
or loose drive belts can permit slippage which is not easily detected.
Several cooling systems make use of a clear plastic container, which
is connected to the radiator just under the pressure cap. This reservoir
is used to store extra coolant and accept coolant from the radiator when
the engine heats up. The coolant inside the radiator expands and is
forced out of the radiator through the pressure cap and is stored until
it is needed. When the engine cools down there is a vacuum created and
the needed coolant is then "sucked" back into the radiator to
maintain the proper level.
The radiator cap acts as more than just a "lid" for your
radiator; it keeps your engine cool by sealing and pressurizing the
coolant inside it.
What makes the radiator cap special is that it is designed to hold
coolant in your radiator under a predetermined amount of pressure. If
the coolant was not kept under pressure, it would start to boil, and
soon you would have boiled all your coolant away.
However, the radiator (or pressure) cap prevents this from happening
by exerting enough pressure to keep the coolant from boiling. Water
boils at 212 degrees F, but if the pressure is increased, the boiling
temperature is also increased. What makes this important is that the
higher the temperature of the coolant is, the greater the temperature
gap between it and the air temperature is. The hotter the coolant is,
the faster the heat in it moves to the radiator and the air passing by.
So a cooling system under a predetermined amount of pressure takes heat
away from the engine faster, which makes it more efficient.
If the coolant pressure becomes too great it can "blow it's
top". To prevent this the radiator cap has a pressure relief valve.
The valve has a preset rating that allows it to take just up to a
certain amount of pressure. When this level is reached the pressure
forces the spring to collapse and allow the excess pressure (and
coolant) to flow by to the "overflow
bottle".
Note: Most newer car radiator caps are not meant to be removed.
Coolant should always be added through the expansion
(overflow) tank. NEVER REMOVE THE RADIATOR CAP FROM A HOT
ENGINE. REMOVING THE PRESSURE CAN CAUSE STEAM TO SHOOT OUT AND SERIOUSLY
BURN YOU.
The reason coolant is routed through the radiator is to allow air to
pass through it and cool it. When you're driving fast enough, the air
rushes through the grill of the car and passes over the radiator core.
If you're stuck in traffic or driving slowly you need something to
"Pull" the air over the radiator. This is the reason for
cooling fans.
Fans are usually mounted just behind the radiator, there are two
types of cooling fans:
- Belt powered fans
- Electric powered fans
Both are explained below.
The fan's activity is not always necessary, and it takes power from
the engine to turn. For this reason a thermostatic control, or fan
clutch, is often used. A different type of fan uses centrifugal force to
move its flexible plastic blades, by flattening them when the engine rpm
is high (flexible-blade fan). The less angle the blade has, the less
power they use.
A fan can have from four to six blades to suck the air through the radiator.
Often the radiator has a shroud for the fan to keep it from
recalculating the same hot air that has collected behind the radiator.
Front-wheel drive engines usually use electric fans to cool the
engine. The radiator is located in the usual place, but an electric
motor drives the fan. A thermostatic switch is used to turn the fan on
and off at predetermined temperature settings, that it senses. The
exception to this is air conditioning. If you turn on the air
conditioner, you bypass the thermostatic switch, and the fan runs
continuously. The reason for this is that the Condenser (same function
as a radiator with the exception that it's cooling a refrigerant) needs
to be cooled also.
Coolant Flow through Radiator and Engine Block
Just like your body needs to warm up when you begin to exercise, your
car's engine needs to warm up when it starts each time.
The thermostat provides control for your engine's warm-up period.
The thermostat is located between the engine and the radiator. This
little temperature-sensitive spring valve stays closed during engine
warm-up. When the thermostat is closed, it prevents coolant from leaving
the engine and circulating through the radiator until the correct
operating temperature is reached. The correct operating temperature for
most engines is between 180 degrees f and 200 degrees F. When the right
temperature is reached, the spring valve opens, allowing coolant to
circulate through the radiator to be cooled.
The temperature at which the thermostat is designed to open is called
its rating, and may be stamped on the body. The 180 degree F thermostat
begins to open at (you guessed it!) 180 degrees F and is fully opened at
200 degrees F. Different engines use different temperature calibrated
thermostats.
There are a few high range thermostats that maintain engine operating
temperatures above 200 degrees F. This causes the engine to burn up more
pollutants and aids in emission control. The Range is set by the
manufacturer of the engine. (Do not install a higher rated thermostat
than is recommended)
Depending on the air temperature, the engine should take from five to
fifteen minutes to warm up. If your engine takes a long time to warm up,
or if it always runs hot, you might need to test the thermostat. A
malfunctioning thermostat can cause excessive engine wear and waste
fuel. A good time to have your thermostat checked is just before summer
or winter.
Hoses are used to connect the engine and the water pump to the
radiator. Radiator hoses are made of flexible rubber; size varies
depending upon the type of engine. Smaller hoses run to the heater
core, these are known as heater hoses.
There are three types of hoses:
- The common hose,
- The molded or shaped hose
- Accordion type hoses
All of these hoses may have spiral wire in their construction. Spiral
wire can be molded or inserted into the hoses, in the required shape,
when the hose is constructed.
The common hose is straight and cannot take much bending before
collapsing. It is made of rubber with fabric reinforcement.
Molded or shaped hoses are the same as the common hose with one
exception. They will not collapse when bent, because all of the bends
that they need are already molded into them.
Accordion type hoses not only put up with severe bending, but they
also absorb some of the vibration between the engine and the radiator.
When our bodies feel cold, we put on a jacket. Our car engines wear
permanent jackets for the opposite reason -- to keep cool!
The water jacket is a collection of passages within the block and
head. These passages let the coolant circulate around the "Hot
spots" (valve seats and guides, cylinder walls, combustion chamber,
etc.) in order to cool them off.
The engine block is actually manufactured in one piece with the water
jackets cast into the block and cylinder head. At normal operating
temperature, the water pump forces the coolant through the head gasket
openings and on into the water jackets in the cylinder head. It flows in
there, cooling everything off by absorbing the heat. After doing its
job, the coolant flows through the upper hose to the radiator where it
releases the heat. Then the water pump sends it back down into the
engine's water jacket to continue the cooling process.
On the sides of the engine are "Freeze" or
"expansion" plugs, which are sheet metal
plugs pressed into a series of holes in the block. These are designed to
hold the pressure of the cooling system, but to pop out if the coolant
in the block ever freezes.
The heater core is mounted under the hood or under the dash board.
Some of the hot coolant is routed through this little radiator, by more
hoses. A small electric fan is also mounted there specifically for the
purpose of directing the heat inside the car. The principle is exactly
the same as the one used in the radiator of your engine, except that the
heat is released inside the car instead of outside. Most engines use the
heater core to warm the air coming from the air conditioner if the dash
setting is not on "cold".
If your car is running hot, turning the heater on will help to reduce
the heat in the engine.
Freeze plugs (also called "blind" or "expansion
core" plugs) are small steel plugs used to seal the holes in the
engine block and head made in casting. They expand and flatten as they
are driven into place, and make a tight seal. These are designed to hold
the pressure of the cooling system, but to pop out if the coolant in the
block ever freezes.
If you have a leak in your cooling system, and you can't find the
leak from the Radiator, or the Water pump, check the freeze plugs they
may be the problem.
Since it is critical for you to keep an eye on the temperature of the
coolant in your cooling system at all times, your car will have either a
gauge or a warning light located on the instrument panel or dashboard.
The question is, how does the information about your coolant get to the
gauge? It gets there, or is sent by the temperature sending unit.
The temperature sending unit is a device that is placed so that it
can determine the temperature of the engine coolant. Simply put, its
resistance to electricity changes with increases and decreases in the
temperature of the coolant. The electric resistance changes control the
movement of the indicator needle on the temperature gauge.
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