Cooling System Overview
Below is an overview of this system's operation
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.
|
