Free Auto Repair Advice by Professional Mechanics
How Does it Work /
Radiator Cooling
System
How an Engine Cooling System Works
Inside your car's engine, thousands of controlled explosions called
combustion events are caused by igniting the fuel / air mixture inside the
engine. These explosions are converted into power through the engine while
producing a large amount of heat. These high temperatures are controlled with
the help of the cooling system. A cooling system consists of a
water pump,
thermostat, radiator hose, hose clamps, radiator, radiator cap and coolant. Your
vehicles cooling system is crucial to making the engine last longer and perform
better. An improperly maintained cooling system can result in the overheating of
the engine, which in turn can cause major component failures within. The cooling
system is a pressurized, sealed circulation system that consists of 6 major
components.
Anti-freeze/Coolant: The fluid in your cooling system is used
as a way to dissipate the tremendous amount of heat an internal combustion
engine creates. Most new vehicles have an optimum operating temperature of
around 200 degrees Fahrenheit or about 93 degrees Celsius; water boils at 212
degrees Fahrenheit, or 100 degrees Celsius and freezes at 0 Celsius or 32
degrees Fahrenheit. That is where Ethylene Glycol
comes in; it is used as a stabilizer to help keep the mixture in the cooling
system from boiling or freezing depending if the vehicle is in use. Ethylene
Glycol in a 50% mixture with water can change the freezing point from 32 degrees
Fahrenheit or 0 Celsius, to –35 degrees Fahrenheit or – 37 Celsius. It moves the
boiling point from 212 degrees Fahrenheit or 100 degrees Celsius to 223 degrees
Fahrenheit or 106 degrees Celsius. Pressure
is the second way that the boiling point is raised; most vehicles have
between 13-15 psi (pounds per square inch) in the cooling system. This can raise
the boiling point of the fluid mixture approximately 45 degrees Fahrenheit or
just over 7 degrees Celsius.
Water pump: The water pump is a mechanical pump that
circulates the engine coolant/anti-freeze through the radiator and back to the
engine. Since they are mechanical pumps, they are usually driven by an
accessory drive belt or by the timing belt/chain (depending on the vehicle).
Thermostat: the t-stat is a temperature sensitive
orifice in the cooling system that opens and closes according to engine
temperature to regulate the flow of coolant/anti-freeze through the radiator and
back to the engine. This allows for the engine to be run at specific
temperatures to optimize the performance and emissions levels of the vehicle.
Radiator: The radiator is basically a finned box
mounted at the front of the vehicle that the coolant is forced through so that
air may pass across it and cool the anti-freeze/coolant. They are covered in
fins that act as heat syncs to help dissipate the heat.
Cooling fan: The cooling fan is located directly
behind the radiator, whether the vehicle is front or rear wheel drive. Its job
is to pull air through the radiator at lower vehicle speeds to keep it from
over-heating. Cooling fans can either be mechanical (belt driven on the engine)
or electric (mounted on the radiator, temperature controlled)
Drive belts/hoses: All of the antifreeze/coolant in
your vehicle is pumped through several hoses. Maintaining them is crucial to
preventing serious engine damage from over-heating. Visually inspect the hoses
for leakage, cracks or abrasions and the general integrity of the hose; they
should be slightly pliable when squeezed with your fingers.
Replace any that are questionable. The drive belt/belts should be
inspected regularly as well.
Typical Engine Cooling System
The engine's combustion chamber can reach temperatures of up to four thousand
five hundred degrees Fahrenheit. About thirty percent of the fuel is converted
into actual power, and about seventy percent is spent into heat. A cooling
system protects an engine from damage by transferring heat to the atmosphere by
using the
radiator. A correct operating temperature is critical for the proper
function of the engine. The thermostat controls when coolant is allowed to flow
into the radiator and back into the engine. Manufacturers have found that a 195
degree thermostat is optimum for efficiency. Below this threshold the catalytic
converter will not work to capacity and will produce increased emissions. The
water pump circulates the coolant from the engine to the
radiator where it is cooled. Automatic transmission vehicles utilize
a fluid cooler inside the engine coolant radiator. This cooler is use to cool
the transmission fluid that has been heated from normal usage.
Engine coolant is used to transfer heat from the
engine to the
radiator by the
cooling system. The radiator removes heat from the coolant by forcing air
through the radiator fins. Without coolant your engine will overheat and
if left unattended, severe engine damage will occur. Coolant colors can vary
from green, orange, blue and yellow each having their own protective properties.
(Note: coolant and antifreeze refer to the same product, in
below freezing, coolant lowers the freeze point hence the name anti-freeze and
in warm weather coolant helps raise the boiling point, "coolant")
Red and Green Engine Coolant
A water pump is used to circulate water throughout the
engine block,
cooling and
heater systems. The water pump is driven by the engine via
multi rib belt in most cases. When a water pump fails it can produce a
squeaking or rattling sound. Also, a water pump can
leak engine coolant through a relief port that allows coolant to pass when
the shaft seal fails. This port is created so engine coolant will not
contaminate the shaft bearings causing a worst problem. If a failing or failed
water pump is allowed to operate it can cause the engine to overheat or
completely fall apart causing cooling system or other internal engine damage.
The water pump circulates coolant continuously, a
thermostat is used to control the rate of coolant flow through the
cooling system . A water pump is comprised of a main housing body, flange,
main shaft, bearings, impeller, seals and a gasket to seal in against the block.
When engine RPM increase so does the water pump flow rate. A water pump will
typical last between 60,000 and 100,000 miles. When replacing a water pump
always insist on high quality replacement parts to avoid premature failure. To
check your water pump condition, make sure the engine is off, next grab a hold
of water pump flange and try to move it back and forth. There should be little
to no play in the main shaft bearing. If excessive play exists the water pump
has failed and needs replacement.
CHECKING THE WATER PUMP
Inspecting your water pump is another small thing that can
save you big down the road. If the accessory drive belt drives your pump then
you have it a lot easier. Look down the pulley for mis-alignment; this can be an
indicator that the bearing is going out, letting the pulley move under the belts
tension. Most water pumps have what is called a “Weep” hole; the weep hole lets
coolant out that is making it into the bearing area of the pump, thus creating
the leak we see on the ground. If the pump is driven by the timing belt or
timing chain, then inspection can be a lot tougher. Look for dried fluid under
the pump area as well as fresh fluid. Water pumps can be tricky; sometimes they
will only leak if the engine is running, so when the fluid leaks out it either
dries on the engine or is blown away by the air circulating under the vehicle.
Water Pump (appearance will very)
The thermostat in your vehicle is what regulates how fast the engine warms up
and at what operating temperature it will run. Warming the engine up is very
important due to the different expansion rates of all the internal parts
(aluminum, steel, cast iron and rubber seals). If an engine is running too cold,
the tolerances within are not correct and damage may ensue. Just as important is
that the engine runs at the proper temperature. Today’s vehicles are designed to
run anywhere between 200-220 degrees Fahrenheit, it is the thermostats job to
regulate the fluid flow through the radiator to keep the temperature at a
predetermined level. Most fuel injected vehicles use a 195-degree thermostat, so
by 200 degrees it is fully open and letting the fluid flow through the radiator
and back to the engine.
In the beginning, water was used for cooling systems, as it is the most
efficient fluid to absorb and dissipate heat. The disadvantage of using water is
that it freezes, boils, and will cause rust. Then water was mixed with ethylene
glycol, which worked as an anti-freezing agent, it also increased the boiling
point of the mixture dramatically. Ethylene glycol can be heated up to 250°F
before becoming ineffective. The cooling system is pressurized to 18 psi. to
increase coolant boiling point which adds 9 degrees Fahrenheit to the boiling
point of the coolant. Coolant is also used to avoid corrosion. An engine
thermostat is designed to regulate the flow of coolant from the engine to the
radiator. This temperature sensitive valve is designed to open when the engine
has reached operating temperature (190°-198°
F). The operating temperature of 190°-230°F
is used to help facilitate fuel combustion for optimum efficiency. When a
thermostat fails it will either stop the coolant flow at operating temperature
"stick closed" or fail to stop the coolant flow causing the engine to run cold
longer than necessary. If the thermostat fails "open" it will cause the coolant
to continuously flow through the engine causing a
diagnostic trouble code (check
engine light) to be set by the computer. When a thermostat sticks closed it
will cause the engine to overheat quickly, usually within 5 to 15 minutes of
operation. To check for either of these conditions, drain coolant and remove the
thermostat (under the thermostat housing) if you are unsure of the location of
the thermostat on your engine consult a
car repair manual. Once you have removed the thermostat inspect the
condition of the main body check for any cracks or broken pieces and check the
valve to make sure it is closed. If the valve is open the thermostat has failed
and needs to be replaced. To check the operation of the thermostat prepare a pot
of water on the stove deep enough to cover the thermostat completely. Place the
thermostat in the pot of water, turn the stove on a medium/high flame, the
thermostat should open right before the water comes to a boil. If the water has
boiled and the thermostat valve is still closed the thermostat has failed and
needs to be placed.
Engine Thermostat
The engine-cooling fan in your car is designed to move air through the
radiator when the vehicle is at slower speeds. This airflow removes heat from
the coolant created by the engine using the radiator as a conductor. Some
radiator cooling fans are powered by the engine (mechanical) or by electricity.
When a cooling fan fails it causes the coolant to retain heat, forcing the
engine to run hot and eventually overheat. A cooling fan that is powered by the
engine is engaged and disengaged from operation by a temperature controlled fan
clutch. This fan clutch is constructed using a silicone grease and temperature
sensitive coil spring that expands and contracts with heat. As the spring
absorbs heat it expands engaging the clutch fan utilizing engine power to drive
the fan. A clutch fan can fail one of two ways; it can either be locking the fan
to the clutch causing poor mileage and a whirring sound, like an airplane is
taking off next to you. Or the silicone grease can start to leak causing the fan
clutch not to lock up allowing the fan to "freewheel", failing to pull air
through the radiator. To check for this condition the engine must be off, and
then inspect the fan clutch for leakage at the front or rear of the unit (input
shaft and temperature controlled expansion spring). If leakage is observed the
fan clutch has failed and needs replacing. Next, take the fan blade and turn it,
the fan blade should free wheel, if you cannot turn the fan blade the clutch has
locked up and needs to be replaced.
Engine Fan Clutch (fan blade not attached)
To inspect an electric
motor cooling fan start with key off, engine off. Spin the fan
blade; it should "freewheel" if the fan motor does not spin it has failed and
needs to be replaced. If the fan motor "freewheels" the electrical system that
operates the fan needs to be tested. Start the engine and turn the air
conditioner to the coolest setting, if your car does not have an air conditioner
skip this step. Within three minutes of operating the cars air conditioner the
cooling fan should activate, if not the fan motor
fuse must be checked first; if the fuse condition is ok the remainder of the
electrical system must be checked. To further troubleshoot this problem a wiring
schematic is needed which is located in a
car repair manual. Use the wiring schematic to trace the circuit through the
fuse and relay components, if everything tests ok the fan motor has failed and
needs to be replaced..
Radiator Cooling Fan
The
radiator in your car is where the actual cooling of the engine occurs
via heat transfer. Engine coolant is forced through the radiator where it is run
through small aluminum tubes with cooling fins. These aluminum tubes direct the
flow of coolant through the radiator and act as the conductor by which the heat
is dissipated. The amount of heat transferred from the coolant depends on the
surface area of the core. The radiator cap acts like a pressure release valve,
as the pressure increases due to heat, the cap allows the excess coolant to
enter the reservoir. Then, when the engine has cooled the coolant will return to
the radiator. Most radiators are made of an aluminum core and plastic side
tanks, but in older vehicles they may be an all-metal construction.
Inspecting Hoses
Part of any routine maintenance schedule should be the
inspection of the cooling system hoses. When visually inspecting the hoses there
are a few things to look for:
- Oil saturation
- Cracks
- Abrasions (from contact with moving parts)
- Seepage
- Clamp tension
Now that you have visually inspected the hoses,
it’s time to give them a squeeze. Hoses can deteriorate internally, they should
feel firm, if too pliable then replace, the same goes for too hard. Regardless
of condition it is a good practice to replace them at the manufacturers
suggested intervals
Basic Checks
Low levels of coolant can lead to problems related to engine overheating. Always
maintain proper levels of coolant in the overflow coolant reservoir tank. ONLY!
Check the radiator when the engine is cold. Only add antifreeze and reinstall the
cap properly. Always drain and refill your
cooling system regularly.
How Does it Work
/ Radiator Cooling
System
Check Manufacturer Specific Radiator
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