cooling systems Flashcards
4 functions of the engine cooling system
remove excess engine heat from combustion process
regulate engine temp
remove heat from other sources. engine oil coolers, hyd cooler, torque converter and coolant to air after cooler
allow for fast engine warm up
1/3 rule of cooling systems
33% of heat from burning fuel used for power
33% is absorbed and radiated by cooling system
33% is radiated to atmosphere by exhaust
3 methods of heat transfer
convection
conduction
radiation
convection
movement of liquid or gas from hot area to cool area
radiation
heat dissipation through vibration of molecular structure
conduction
heat transferred from one molecule to another within an object
examples of good heat conductors
copper ,aluminium, cast iron ,steel
examples of poor heat conductors
glass , wood , air
liquids will boil at higher altitude because
there is less pressure acting on the surface of the liquid
pressure in a cooling system will allow the coolant to
exceed the normal boiling point
1psi of pressure will raise the boiling point
3 F
increased pressure will also improve
heat transfer and reduce aeration and cavitation
advantage of air cooled systems
.lighter engine weight
.reduced system maintenance
.reduced complexity
.elimination of coolant leaks cavitation corrosion and antifreeze agents
disadvantage of air cooled systems
louder operation
temp may be affected by ambient temp
cooling fins on air cooled engines
offer increased cooling surface area
engine drive fan or cooling blower
may be controlled by heat sensing device
shrouds,metal shields and baffles
direct air past cooling fins in a determined direction and velocity to maintain even engine temp
integral flywheel cooling fan
operates at the same speed as the engine cannot be changed
dirt and dust build up on cooling fins
dissipate the engines ability to reduce heat
advantages of liquid cooled engine
.cooling is more uniform
.reduced noise
.controlled engine temp allows bearing to have tighter clearance
.reduced distortion of components due to even heating
engine coolant must
absorb and carry away excess heat generated by the engine
must not allow corrosion to form in cooling passages
must remain a liquid during engine operation in cold climates
scale and rust deposits will
act as an insulator
1” thick cast surface with 1/16 thick deposit of scale is equal to
4” thick cast in heat transferability
antifreeze products are manufactured with
petroleum products and should be considered toxic
three methods for glycol testing
anti-freeze hydrometer
litmus paper
refractometer
when operating engines in moderately cold temp
50/50 anti-freeze to water should be used
coolant with more than 60% antifreeze can cause
gelling of the coolant
reduced heat transfer ability
higher boiling point
corrosion inhibitors often referred to as
SCA supplemental coolant additives
coolant filters
remove sludge and rust from cooling system to help prevent small cooling passages from being plugged and causing hot spots
small zinc plate in some filters is used for
to focus electrolytic action on the plate and not on cylinder liner walls or rad cores
down flow radiator
consist of a top tank central cooling core and bottom tank
horizontal flow tank
have two side tanks and a central cooling core
central cooling core construction
one piece or multi piece construction composed of individual cooling pipes that are finned to improve heat transfer
single pass process rad
coolant enters in one direction and leaves the rad core in one cycle
low flow or multi path rad
coolant remains in rad longer
first flows in one direction then in the opposite direction through a separate cooling section until it leaves the rad
radiator core
main heat exchanger used in the engine cooling system
de-aeration tubes
remove small air bubbles from coolant during operation
materials used for rad tank
copper brass cast iron cast aluminium plastic/fiberglass sheet steel
two types of rad core design
tube and fin
honeycomb
rad tank design depends on
application, cost, cooling efficiency
surge tank operation
acts as a remote reservoir
used when temp and pressure changes
has pressure cap to allow it to breath when coolant expands and contracts
has sight glass to check coolant level hot or cold
when checking coolant at the rad
must be done when coolant is cold and on level ground
advantages of coolant recovery tank
greater positive head pressure to coolant pressure
space for vapor to condense back to liquid
minimizes aeration by keeping rad full
reduces corrosion and rust
pressure caps protect the cooling system from
dangerously high pressures
vacuum from cooling coolant
coolant that is full of air bubbles
wont be able to cool an engine as well because air is a shit insulator
thermostats
regulates engine coolant temp and allows for faster engine warm up
normally located near the top of cylinder head
three types of thermostats
bypass
partial blocking
full blocking
bypass thermostats
allows about 25% of coolant to circulate through rad when cold
will lengthen time required to warm up engine
partial blocking thermostats
allows about 10% of coolant to circulate through to rad
full blocking thermostat
allows no coolant to pass through to rad
allows for faster engine warm up
thermostat operation
is a heat sensitive valve that opens gradually when coolant heats up allowing for regulation of engine temp
coolant bypass operation cold
when coolant is cold and thermostat is closed bypass tube will allow coolant to re circulate in engine and will cause faster warm up
coolant bypass operation warm
when engine has reached operating temp bypass tube will be fully closed allowing flow of coolant through rad
cooling shutter systems
will open and close with engine temp
when closed no air will flow over rad fins
full open allows for full flow of air over fins
shutter operation
controlled by a shutterstat
when temp rises shutterstat opens allowing air pressure , vacuum , or engine oil pressure to overcoming spring force holding shutters closed
cooling fans
often connected to water pump assembly
if water pump is gear driven then fan will be belt driven at a separate location
fan shrouds
ensure air is pushed or pulled through rad core
prevent air from recirculating around fan tips
shrouds should cover 1/3 to 2/3 of fan pitch
fan blade spacing
reduces fan noise and maintains balance
push type fans
prevent debris build up from plugging rad core
forces air from engine compartment through rad core
reversible fan type
fan blades can be manually changed from push to pull type
fan guards
must be around fan at all times to protect personnel and rad core
thermostatic fans
operate only when they need to
prevent parasitic load on engine
general temp for thermostats to open
185’F
general temp for shutters to open
190-195’F
general temp for fans to begin operation
200’F
fans can create a parasitic load on engines of between
9 to 40 horsepower
water pump
creates a positive circulation of coolant through the engine at all times
can be gear or pulley driven
localized over heating could be the cause of
scale and corrosion build up causing reduced pump flow
