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The Cooling System
The
purpose of the engine's cooling system is to remove excess heat
from the engine, to keep the engine operating at its most efficient
temperature, and to get the engine up to the correct temperature
as soon as possible after starting. Ideally, the cooling system
keeps the engine running at its most efficient temperature no matter
what the operating conditions are.
As
fuel is burned in the engine, about one-third of the energy in the
fuel is converted into power. Another third goes out the exhaust
pipe unused, and the remaining third becomes heat energy.
A
cooling system of some kind is necessary in any internal combustion
engine. If no cooling system were provided, parts would melt from
the heat of the burning fuel, and the pistons would expand so much
they could not move in the cylinders (called "seize").
The
cooling system of a water-cooled engine consists of: the engine's
water jacket, a thermostat, a water pump, a radiator and radiator
cap, a cooling fan (electric or belt-driven), hoses, the heater
core, and usually an expansion (overflow) tank.
Fuel
burning engines produce enormous amounts of heat; temperatures can
reach up to 4,000 degrees F when the air-fuel mixture burns. However,
normal operating temperature is about 2,000 degrees F. The cooling
system removes about one-third of the heat produced in the combustion
chamber.
The
exhaust system takes away much of the heat, but parts of the engine,
such as the cylinder walls, pistons, and cylinder head, absorb large
amounts of the heat. If a part of the engine gets too hot, the oil
film fails to protect it. This lack of lubrication can ruin the
engine.
On
the other hand, if an engine runs at too low a temperature, it is
inefficient, the oil gets dirty (adding wear and subtracting horsepower),
deposits form, and fuel mileage is poor-- not to mention exhaust
emissions! For these reasons, the cooling system is designed to
stay out of the action until the engine is warmed up.
There
are two types of cooling systems; liquid cooling and air cooling.
Most auto engines are cooled by the liquid type; air cooling is
used more frequently for airplanes, motorcycles and lawnmowers.
Liquid
cooled engines have passages for the liquid, or coolant, through
the cylinder block and head. The coolant has to have indirect contact
with such engine parts as the combustion chamber, the cylinder walls,
and the valve seats and guides. Running through the passages in
the engine heats the coolant (it absorbs the heat from the engine
parts), and going through the radiator cools it. After getting "cool"
again in the radiator, the coolant comes back through the engine.
This business continues as long as the engine is running, with the
coolant absorbing and removing the engine's heat, and the radiator
cooling the coolant.
A
cooling system pressure tester is used to check the pressure in
the cooling system, which allows the mechanic to determine if the
system has any slow leaks. The leak can then be found and fixed
before it causes a major problem.
The
Heater Core
The
heater core is a smaller version of the radiator that is used to
keep your toes warm when it's cold outside.
The
heater core is mounted 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 especially for the purpose of directing
the heat inside the car. To turn this fan on, you use a switch called
"fan" or "blower," located on your control panel.
The principle is exactly the same as the one used in the radiator
for 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". More efficient designs don't do this because it
makes the engine work harder than it has to. They cycle the compressor
on and off to lessen the cooling output.
If
your car is running hot, turning the heater on will help to reduce
the heat in the engine. Unfortunately, most cars don't overheat
in the winter.
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