2 cooling system theory
Transcript 2 cooling system theory
Cooling System Theory
ADX 150 – Engine Repair
ADX 170 – Climate
Normal operation produces heat that must
be carried away by coolant
Cooling system transfers heat to cooler
outside air when engine is hot.
Cooling system keeps heat in the engine
when engine is not warm enough.
Modern cooling systems are designed to
maintain an even temperature of about 180
to 230°F (82 to 113°C).
Cooling System Operation
System design removes 35% of total
If not equipped with factory A/C, cooling
system is usually not able to handle
additional heat load of aftermarket units.
COOLING SYSTEM COMPONENTS
• Water Pump
• Cooling Fan
• Pressure Cap
• Clamps and hoses
• Overflow tank
Centrifugal Type Water Pump.
Inlet comes from bottom of Radiator.
Outlet is through impeller to engine.
Water Pump Replacement can be due to
leaks or bearing failure.
Transfer pump parts and use correct
Coolant will often
leak out of the weep
This indicates the
shaft seals in the
water pump have
replacement will be
Water pumps can be driven off of the
serpentine belt, the timing belt, or the
When driven off of the timing belt, most
technicians suggest replacement when
replacing the timing belt.
Allows for heat to move from coolant to the
Cooler air flowing through the radiator cools
Most radiators about 28-35 sq. feet.
Can have multiple cores to increase area.
- Cross flow
- Down flow
Many radiators will have oil coolers built
These can be for the engine oil or the
Should either of these crack, oil could
get into the coolant and coolant into the
Radiator pressure results from the
expansion of the coolant as the engine
A small amount of air used to be kept in the
radiator to allow for this expansion.
Since air leads to rust and corrosion, the
radiator needs to be filled completely with
The pressure cap and coolant reservoir
work together to allow for this expansion.
The upper gasket prevents
coolant from escaping to the
outside. The lower gasket
keeps a pressure in the
radiator. The cam lock pushes
the two gaskets against the
sealing surfaces when the cap
is installed. The safety stop
prevents the cap from being
opened too quickly.
Pressurizing a liquid
increases the boiling
point of that liquid.
Cooling systems are
pressurized so that
the boiling point of
the coolant is raised.
pressurized to 15 psi.
The coolant’s boiling point
increases about 3° F for each
psi increase in pressure.
The pressure cap allows the pressure to
build, and release past a specified point.
• Equipped with Vacuum and Pressure Valve
• Used to raise Pressure in system
The pressure cap also improves the
operation of the water pump.
By keeping the radiator pressurized, the
water pump has a constant supply of
coolant to draw from.
If pressure became too low, the coolant
would boil and the water pump would
draw only air.
Contains reserve coolant.
When cap releases coolant due to
coolant expansion, coolant goes to
When cooling system cools off and
creates a vacuum, coolant is pulled from
Some closed cooling systems do not
have a cap on the radiator.
The overflow tank is pressurized with the
rest of the cooling system.
The coolant level will be checked in the
Systems with a pressurized overflow
tank keep a small amount of air in the
This allows the coolant to expand and
compress the air.
Most tanks like this will have a pressure
cap on the tank and no cap on the
Odd Cap Location (Durango)
Opening a Hot System
Slowly turn the cap with a rag and do not
turn it past the safety lock.
Speeds up engine warm up.
Regulates flow and temperature of engine
Most are on the outlet side of coolant flow.
Maintains optimum engine operating
temperature for best emissions and
temperature is the
Thermostat should be
fully open 20°F above
195°F thermostat =
fully open at 215°F
180°F thermostat =
fully open at 200°F
The thermostat contains a wax pellet on
the engine side of the thermostat.
Wax melts and expands when engine
As the wax expands, it overcomes spring
pressure and opens the valve.
have a “jiggle pin”
that should be
installed at the top
to aid in bleeding air
from the system.
Clamps and Hoses
Hoses direct coolant from the engine to
the radiator, heater core, and the
Clamps hold hoses in place.
Preformed hoses are made specifically
for an application.
Flex hoses are used for a variety of
Some lower radiator hoses contain a
spring to prevent them from collapsing
due to water pump suction.
The water pump pumps coolant through
If the thermostat is closed, coolant flows
through the block, heater core, and the
The bypass leads back to the water
There will be no flow through the radiator
when the thermostat is closed.
is directed back
into the block
Some thermostats are designed to block off
the bypass passage when they are open.
When the thermostat is open, coolant is
then allowed to flow from the block to the
upper part of the radiator.
The coolant is then cooled in the radiator.
The water pump draws the coolant out of
the bottom of the radiator so that it can then
be circulated throughout the block to cool
When an engine cylinder block and head are
cast, cavities called water jackets are formed
around the cylinder walls and combustion
These water jackets allow coolant to circulate
around the very hot areas, including the exhaust
valve seats, as well as the relatively cooler areas
of the lower cylinders.
The coolant absorbs heat from the hot areas and
transfers this heat to the colder areas in the
engine or radiator.
Some manufacturers position the thermostat on
the inlet side of the water pump.
As the cooled coolant hits the thermostat, the
thermostat closes until the coolant temperature
again causes it to open.
This reduces thermal cycling (expanding and
contracting of the metal).
Thermal cycling can damage aluminum engine
A modern style cooling system
showing how the coolant flows
through the block first, then
through the cylinder head, and
finally through the radiator
after the thermostat opens.
Block heaters are small, electricalresistance heater units that can be mounted
in the block.
These heaters are plugged into ordinary
110-volt ac outlet and are used in very cold
areas to warm an engine while it is shut off.
Block heaters provide easier engine starting
and faster warm-up, especially for diesels.
heaters install in
one of the core plug
Aftermarket Block Heaters
Aftermarket block heaters generally
should not be installed in late model
The computer checks the ambient air vs.
the coolant temperatures after sitting for
If the two disagree, the MIL will
illuminate and a DTC will set.