The Engine Cooling System

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The Engine Cooling System
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Coolant flows through the engine to absorb excess
heat.
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An ethylene-glycol concentration up to 68 percent
offers the best protection against freezing.
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Ethylene-glycol coolant has a high boiling point.
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Pressurizing the coolant system raises the
boiling point of the coolant.
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Components and flow patterns of a typical cooling
system.
TECH TIP
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Hot/Cold/Hot/Cold Heater Diagnosis A common
customer complaint is a lack of heat from the
heater but only while driving, even though there
seems to be plenty of heat when the engine is at
idle speed and the vehicle is stopped. This is a
classic symptom of low coolant level. The lower
than normal coolant level in the radiator
prevents enough flow to supply the heater
core. When the engine speed is reduced, the water
pump turns slower and coolant can more easily
flow through the heater core resulting in heat
from the heater. As the engine speed increases,
the water pump speed also increases. Because
there is less than the proper amount of coolant
in the system, the water pump will only be able
to supply coolant through the engine (a path of
lower resistance).
BACK
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Many engines are equipped with a bleeder valve to
permit a technician to bleed any trapped air from
the cooling system. The valve is loosened as
coolant is poured into the system. Because air is
lighter than coolant, the air tends to float
toward the highest part of the cooling system.
Frequently Asked Question
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How Can You Easily Burp Air from the Cooling
System? The first step in being certain there is
no air in the cooling system is to try to avoid
getting air into the system in the first place
during cooling system service. If the engine is
equipped with bleeder valves near the high spots
of the cooling system, these valves should be
open when refilling the radiator. Any trapped air
will always travel to the highest portion of the
cooling system and escape out of these bleeder
openings. Close the valves as soon as coolant is
observed coming out of the valve opening.
Frequently Asked Question Navigation
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If the cooling system is not equipped with
bleeder valves, fill the cooling system as full
as possible and then start the engine. With the
radiator cap removed, the coolant level will
often rise as the trapped air is expanding, then
drop down as the trapped air escapes out of the
radiator neck opening. Air can still remain
trapped. To help speed up the process, try
installing the radiator cap just to the first
notch. (In this position the radiator cap is
closed, but will not seal enough to allow
pressure to build in the cooling system.) To help
force any trapped air from the cooling system,
simply drive the vehicle normally for several
miles. By driving the vehicle under load, the
engine will warm up faster and the thermostat
will open allowing the coolant to flow from the
engine and through the radiator. Any trapped air
is then released into the radiator where it can
easily escape through the unsealed radiator cap.
After filling the radiator, securely tighten the
radiator cap and test drive the vehicle to
verify proper operation.
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Frequently Asked Question Navigation
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The water pump is mounted on the front of the
engine block and is typically belt driven to
ensure constant coolant circulation whenever the
engine is running.
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The water pump impellers spinning blades apply
centrifugal force to move the engine coolant
through the water pump.
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With a cold engine, the thermostat stays closed
(A) to retain pressure and heat as the engine
warms up. When the engine is warm, the thermostat
opens (B), allowing the coolant to travel to the
radiator to be cooled.
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The thermostat is a temperature-sensitive
component that is activated by an integral wax
pellet.
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A typical thermostat location.
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A spring-loaded bypass valve opens under coolant
pressure, while the main thermostat remains
closed.
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The coolant tubes and fins of the radiator core.
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A downflow radiator has vertical tubes and tanks
at the top and bottom of the core.
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A crossflow radiator has horizontal tubes and a
tank on each side of the core.
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The pressure valve maintains the system pressure
and allows excess pressure to vent. The vacuum
valve allows coolant to return to the system from
the recovery tank.
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Most radiator caps are mounted on the top or side
tank of the radiator.
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Some radiator caps are mounted in a remote
location to provide an accessible filling point.
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The recovery tank coolant level depends on the
engine temperature.
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The engine-driven fan draws air into the engine
compartment through the radiator core.
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Electric fans can be mounted directly to the
radiator, as required with transverse-mounted
engines on front-wheel drive vehicles.
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Electric fans can turn on at any time, even when
the engine is shut down. Always disconnect the
power lead before working around it.
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The flexible fan blade changes shape to reduce
operating drag and noise as engine speed
increases.
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The center of the clutch is a fluid-drive that
controls the speed of the fan.
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The bimetallic temperature sensor spring controls
the amount of silicone that is allowed into the
clutch drive. This action controls the speed.
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Radiator hoses must be large enough to carry full
coolant flow, and they must be kept in good
condition to withstand the heat and pressure of
the cooling system and engine compartment.
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Core plugs seal holes that lead to the water
jackets.
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TECH TIP
The heater core is a heat exchanger that is
mounted inside a heater housing on the bulkhead
or inside the passenger compartment under the
instrument panel.
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Might As Well Do It Now Whenever an evaporator is
being replaced, many service technicians also
recommend that the heater core also be
replaced. This is especially true of the vehicle
had a neglected cooling system. Most heater
cores are close to or even have to be removed to
replace an evaporator. The only additional cost
to the vehicle owner is the cost of the heater
core itself.
BACK
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This type of manually-operated heater control
valve is connected to the instrument panel heater
control by a wire cable.
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This vacuum-operated heater-control valve uses a
vacuum motor to mechanically move the valve open
and closed. The vacuum motor responds to vacuum
signals from inside the passenger compartment,
based on settings of the heater control panel.
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END OF SHOW
This engine is air-cooled. Airflow over the
cooling fins absorbs the excess engine heat. The
hot air is then used to warm the passenger
compartment.