Engine Overheating Repair
Inside your car's engine, thousands
of controlled explosions called combustion events occur. These explosions are created
by igniting a fuel / air mixture inside the engine. Spark plugs are used to ignite
the fuel / air mixture contained in the cylinders. 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, cooling fan, thermostat, radiator hose, hose clamps,
radiator, radiator cap and coolant. 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 cooling fins.
Without coolant your engine will overheat and if left unattended severe engine
damage will occur. Engine coolant colors can vary from green, orange, blue,
clear and yellow each having their own unique protective and environmental properties.
Coolant leaks are a common car problem that can lead to overheating; we have listed
some of the most common causes below. (Always inspect the engine cold, coolant is
under pressure and can burn you). (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).
Troubleshooting Procedure
Check Engine Coolant Level, Test For Leaks - Engine coolant
is used to transfer heat from the engine to the radiator; if a
coolant leak is present the engine
will eventually overheat. Inspect the
engine coolant level in the coolant reservoir tank; coolant level should be
between the hot and cold marks. Always check the coolant level when the engine is
cold, preferably over night. If the coolant level is not between the reservoir marks
the cooling system may have a leak.
Radiator Cap and Coolant Reservoir
If engine overheating has occurred the coolant level will naturally be low due
to expansion of the coolant from the extreme heat of the engine. This heat expansion
forces coolant out of the radiator and coolant reservoir. To test for an engine
coolant leak move the car to a dry smooth surface and allow the engine to cool.
Remove the radiator cap and carefully (do not spill) add water until full, then
re-install cap. Start engine and allow to run for about three to five minutes (do
not allow to overheat) while the engine is running inspect the ground below the
engine, if an engine coolant leak is present observe the location of the coolant
drops, this will help determine where to start looking for the coolant leak (shut
the engine off before inspecting).
Leaking Radiator and Radiator Hose
If no coolant is observed two additional checks are needed for a complete test.
With the engine off remove the engine oil fill cap and turn it over, if a
milky oil condensation
is present the engine may have a failed cylinder head or intake manifold gasket
allowing coolant to leak internally. To inspect engine gaskets disassembly is required.
Next, the car heater core must be inspected; the quickest way to check the
heater core condition without removal
the heater core is to inspect the passenger's side foot well compartment carpet
for the presences of coolant. If coolant is present the heater core has failed and
must be replaced or repaired. After necessary repairs have been made refill the
cooling system with manufacturers recommended engine coolant and recheck operation.
Check Engine Thermostat - 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°-210° F is used to help facilitate
fuel combustion. When a thermostat fails it will either stop the coolant flow "stick
closed" and overheat or fail to stop the coolant flow causing the engine to run
colder longer than necessary. If the thermostat fails to "close" it will cause the
coolant to continuously flow through the engine creating a
diagnostic trouble code (check
engine light) to be set. 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 thermostat,
(thermostat is located in 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 cranks or broken pieces, also 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 top deep enough
to cover the thermostat completely. Install 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
Inspect Engine Cooling Fan Clutch or Electric Fan Operation -
The engine cooling fan system in your car is designed to move air through
the radiator when the vehicle is at
slower speeds or stopped. This air flow removes heat from the coolant created by
the engine using the radiator as a conductor. Most radiator cooling fans are powered
by the engine 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 motor is engaged and disengaged from operation by a temperature
controlled fan clutch. This fan clutch
is constructed using a silicon 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 lock the fan to the clutch
causing poor mileage while producing a whirring
sound, like an airplane is taking off next to you. Or the silicon 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 when needed. To check for this condition
the engine must be off, 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 ignition key switch off,
next spin the fan blade by hand, it should "freewheel" if the fan motor does not
spin freely 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 five minutes of the car air conditioner operating 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 repair service
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.
The cooling fan motor failure is the most common repair.
Radiator Cooling Fan
Low Flow Through Radiator - A radiator is used to remove heat
from the engine coolant through convection. Coolant is forced through the radiator
hoses and into the radiator via the water
pump. Inside the radiator many small tubes which are constructed with cooling
fins transfer heat to the atmosphere. If the radiator becomes plugged it fails to
transfer heat from the coolant causing the engine to overheat. This condition generally
occurs gradually over time and will be more noticeable when climbing a grade or
in warm climate. To check for this condition make sure the engine is cold, and then
drain coolant to lower the level in the radiator. The coolant level is lowered to
allow visual inspection of the cooler tubes in the radiator core. If the radiator
cooler tubes are plugged drain the cooling system completely and replace the radiator
with new, reassemble to refill with coolant and recheck system.
Internally Plugged Radiator
Externally Plugged Radiator
Plugged Catalytic Converter - The
catalytic converter or "cat"
for short is one of your vehicles main emission control devices. The name was derived
from the operation the catalytic converter performs; it utilizes a catalyst material
and converts unburned gasses into burned gases, "catalytic converter". The catalyst
is heated to excite the chemical the catalyst is made of, this burns the unburned
fuel making the catalyst even hotter furthering the effect (thermo reactor). Because
of the extreme temperatures the catalytic converter produces the catalyst material
can crack and come apart clogging the outlet port of the converter causing, engine
overheating, low power and
stalling.
Catalytic Converter Starting to Fail
While the catalytic converter is failing it will partially plug the
exhaust system, creating excessive
back pressure in the engine exhaust. Excessive exhaust back pressure will cause
the engine to have less power, to compensate for low power condition the user will
add more throttle. When more throttle is applied the engine creates excessive heat
overloading the cooling system causing the engine to run hot or overheat. This condition
is always accompanied by low engine power.
Plugged Catalytic Converter
If further assistance is needed, our certified car repair technicians are ready
to answer your car questions.
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