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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.
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