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Troubleshooting
/ Engine Overheats
Car Engine Overheating - Troubleshooting
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 engine cold to avoid
personal injury) (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 help raise the boiling point, "coolant")
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. -
Engine Coolant
Leaks
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 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 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. 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 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
For exact specific repair procedures for any of the steps above visit our
online repair
manual page.
Troubleshooting
/ Engine
overheats
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Overheating Questions and Answers
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