Inside your car's engine, thousands
of controlled explosions called combustion events caused by igniting fuel-air mixture
inside the engine generate heat. If this heat is not controlled the
engine will overheat and
internal damage can occur. 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. The thermostat is designed
to control the flow of coolant through the cooling system while the engine is warming
up to operating temperature.
An engine needs to operate at a particular heat range to be efficient. Once the
engine is warm the thermostat will open to allow coolant flow to maintain a particular
temperature. Most thermostats are designed to open at about 195° F but other temperatures
are available for a variety of applications. A thermostat consists of a main housing,
a plunger style of valve with return spring and a temperature sensitive wax filled
plunger that acts as the sensing and activating device. A thermostat maintains engine
temperature as is opens and closes throughout the engine operation.
Engine Thermostat
When a thermostat malfunctions it can stick in the closed position not allowing
the coolant to circulate, causing the engine to overheat. This will cause the vehicle
to overheat in a very short amount of time (about 5 minutes). Or the thermostat
could stick open causing the engine to run too cold. In this case the
service or check engine soon light could illuminate, followed by a
trouble code. To test a thermostat remove unit.
Prepare a pan of water deep enough to cover the thermostat completely. Next install
a temperature gauge into the water along with the thermostat. A cooking thermometer
works well for this.
Next, start heating the water while watching the thermometer, the thermostat
should remain closed until the water reaches 190° at this point the thermostat should
start opening and be completely open at about 195°. If the thermostat stays closed
through the boiling point the thermostat has failed and needs replacing. If the
thermostat is stuck open or broken it has failed and needs replacing. Never run
an engine without a thermostat because the thermostat works as a system flow regulator
as well. What this means is the thermostat has a specific opening that regulates
the flow through the cooling system. If the coolant is allowed to flow too quickly
through the radiator the coolant will not have time to transfer the heat it has
absorbed. This will cause the engine to overheat.
Typical Engine Cooling System
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
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.
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.
If further assistance is needed, our certified car repair technicians are ready
to answer your car questions.
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