Automotive cooling system

1. © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
Publisher
The Goodheart-Willcox Co., Inc.
Tinley Park, Illinois
by
Russell Krick

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 Cooling system functions
 Cooling system operation
 Cooling system types
 Basic cooling system
 Closed and open cooling systems
 Cooling system instrumentation
 Antifreeze
 Block heater

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Remove Engine Heat
 Combustion can reach 4500ºF (2500ºC)
 This is hot enough to melt metal parts
 The cooling system removes excess heat

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Maintain Operating
Temperature
 180ºF to 210ºF (80ºC to 100ºC)
 Ensures that clearances are correct
when an engine warms to operating
temperature, parts expand
 Ensures proper combustion, minimum
emissions, and maximum performance

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Reach Operating
Temperature Quickly
 This minimizes several conditions:
poor combustion (poor fuel vaporization)
part wear
oil contamination
reduced fuel economy
increased emissions

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Heater Operation
 The cooling system circulates coolant to
the vehicle’s heater
 Engine heat is used to warm the
passenger compartment

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Cooling System

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 The water pump forces coolant through
the engine water jackets
 The pump is belt or gear driven off the
crankshaft

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Cold Engine Operation
 The thermostat is closed
 The coolant circulates inside the engine
 The engine warms quickly

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Hot Engine Operation
 At operating temperature, the
thermostat opens
 Heated coolant then flows through the
radiator
 Excess heat is transferred from the
coolant to the air flowing through the
radiator

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 Two common types:
air cooling
liquid cooling

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Air Cooling Systems
 Large cylinder cooling fins and outside
air remove excess heat
 The cooling fins increase the surface
area of the metal around the cylinder
 This allows enough heat to transfer to
the outside air
 Plastic or metal shrouds direct air over
the cylinder fins

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Liquid Cooling
Systems
 Circulate coolant through the water
jackets
 Combustion heat is transferred to the
coolant
 The cooling system carries it out of the
engine

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Liquid Cooling
Advantages
 Precise temperature control
 Less temperature variation
 Reduced emissions
 Improved heater operation

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Air Cooling versus
Liquid Cooling

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Liquid Cooling
Heat is transferred to cylinder wall and then
into the coolant, where it is carried away

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Conventional Coolant
Flow
 Hot coolant flows from the cylinder head
to the radiator
 After being cooled in the radiator, the
coolant flows back into the engine block

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Reverse Flow Cooling
 Cool coolant enters the head and hot
coolant exits the block to return to the
radiator
 Helps keep a more uniform temperature
throughout the engine
 Found on high-performance engines

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 Components:
water pump
radiator hoses
radiator
fan
thermostat

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Water Pump
A ribbed belt powers this pump
Crank
pulley
Water
pump
pulley
Impeller
Ribbed
belt

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Impeller Pump
Coolant is thrown outward by centrifugal
force, producing suction in the center of
the pump housing

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Water Pump Cutaway
Seal leakage will drip from the vent hole

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Coolant Flow

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Coolant Flow
(Conventional)
 Coolant flows out of the radiator,
through the lower hose, into the pump
 It then flows through the pump, around
the cylinders, through the heads, up
through the thermostat, and back into
the radiator

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Hoses
 Radiator hoses
carry coolant between the engine water
jackets and the radiator
the lower hose is exposed to water pump
suction, so a spring may needed to prevent
collapse
 Heater hoses
carry hot coolant to the heater core
smaller diameter than radiator hoses

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Radiator and Heater
Hoses

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Radiator Hoses
Two basic types of radiator hoses

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Hose Clamps
Three basic types of hose clamps

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Radiator
Transfers coolant heat to the outside air

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Radiator Types
Downflow Crossflow

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Transmission Oil
Cooler
 Often placed in the radiator on cars with
automatic transmissions
 Prevents the transmission fluid from
overheating

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Transmission Oil
Cooler
Small tank inside
one of the
radiator tanks

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Oil Cooler System

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Radiator and A/C
Condenser
 The condenser is usually mounted in
front of the radiator
in this arrangement, heat from the
condenser flows through the radiator,
reducing efficiency
 Side-by-side mounting is sometimes
used

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Radiator and A/C
Condenser
This vehicle has
side-by-side
mounting

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Radiator Cap
 Seals the radiator
 Pressurizes the system
 Relieves excess pressure
 Allows coolant flow between the radiator
and the coolant reservoir

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Radiator Cap

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Radiator Cap Pressure
Valve
 Spring-loaded disk
 Normally, water boils at 212ºF (100ºC)
 For each pound of pressure increase,
the boiling point goes up about 3ºF
(1.7ºC)
 Typical pressure:
12–16 psi (83–110 kPa)
raises the boiling point to
250–260ºF (121–127ºC)

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Radiator Cap
Vacuum Valve
Opens to allow flow back into the radiator
when the coolant temperature drops

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 Closed cooling system
uses an expansion tank
overflow tube is routed into reservoir tank
 Open cooling system
allows excess coolant to leak onto the
ground

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Pressure Cap
Operation
Hot engine

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Pressure Cap
Operation
Cold engine

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Cooling System Fans
 Pull air through the core of the radiator
 Increase the volume of air flowing
through the radiator
 Driven by fan belt or electric motor

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Flex Fan
High engine speed causes the blades to
flex, reducing the blowing action

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Fluid Coupling Fan
Clutch
Filled with
silicone-based oil
The clutch slips at
higher rpm

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Thermostatic Fan
Clutch
 Bimetal spring controls clutching action
cold—clutch slips
hot—clutch locks

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Electric Cooling Fans
 An electric motor and a thermostatic
switch provide cooling
 Common on transverse-mounted
engines
 Save energy and increase cooling
efficiency
 Fans only function when needed

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Electric Fan Operation
Cold engine

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Electric Fan Operation
Hot engine

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PCM-Controlled Fans
 When cold, the ECM does not energize
the fan relays
 After warm-up, the ECM feeds current
to the fan relay coils, closing the relay
contacts
 High current flows to fans

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PCM-
Controlled
Fans

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Radiator Shroud
Ensures that the fan
pulls air through
the radiator core

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Thermostat
 Senses the coolant temperature and
controls coolant flow through the
radiator
 Reduces coolant flow in a cold
engine
 Increases coolant flow in a hot
engine

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Thermostat
A temperature-sensitive valve

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Thermostat Operation
 Cold engine
wax-filled pellet has contracted
spring holds valve closed
 Hot engine
when heated, pellet expands
spring tension is overcome
valve opens

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Thermostat Operation
A. Cold engine
B. Hot engine

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Thermostat Operation
Cold engine

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Thermostat Operation
Hot engine

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Bypass Valve
Permits coolant
circulation through the
engine when the
thermostat
is closed

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Bypass Thermostat
Blocks off the bypass at operating
temperature
Impeller
Water pump
drive pulley
Water pump
housing
Thermostat
Main flow
Flow to
radiator
Bypass
spring
Bypass
flow
Main
spring

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 Two common types:
temperature warning light
engine temperature gauge

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Temperature Warning
Light
 When the coolant becomes too hot, a
temperature sending unit (switch) in the
block closes, completing a light circuit
 The warning light glows

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Warning Light Circuit

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Engine Temperature
Gauge
 Shows the exact operating temperature
 Components:
gauge
variable resistance sending unit

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Engine Temperature
Gauge Operation
 When cold, the sending unit has a high
resistance
 Current flow through the gauge is low
 The gauge reads cold
 When hot, the sending unit resistance
lowers
 Current flow through the gauge
increases, the needle deflects to the
right

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 Composed of ethylene glycol mixed with
water
 Prevents winter freeze-up
 Prevents rust and corrosion
 Lubricates the water pump
 Cools the engine

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Corrosion Protection
Protected with
antifreeze
Water only

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Antifreeze/Water
Mixture
Lowers the coolant freezing point
to about –34 ºF (–37 ºC)
50%ANTIFREEZE
50%WATER

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 Aids engine starting in cold weather
 120-volt heating element mounted in the
block water jacket
 Common on diesel engines

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Block Heater
Installation

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Engine and Cooling
System

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Engine and Cooling
System