Mechanics

Cooling System

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Step by step instructions on how an internal combustion engine cooling system works. This article pertains to all vehicles except electric.


Engine Cooling System

There are thousands of controlled explosions called combustion events which are caused by igniting a fuel air mixture inside the combustion chamber. These explosions are converted into thrust throughout the engine while producing an amount of heat. High temperatures would make the engine overheat if not for the cooling system. Visit - Engine overheats. The cooling system is a pressurized, sealed circulation system that consists of seven major components:


Step 1 - Anti-Freeze/Coolant

Fluid is used to dissipate heat away from the engine's block and cylinder heads. Most engine's have an optimum operating temperature of around 200 degrees Fahrenheit or about 93 degrees Celsius. This temperature is maintained using a thermostat which is designed to allow coolant to flow throughout the system. Normal water boils at 212 degrees Fahrenheit, or 100 degrees Celsius, and freezes at 0 Celsius or 32 degrees Fahrenheit, where as coolant boils at 223 degrees and freezes well below 32 degrees. Coolant is also used to avoid corrosion which can damage vital engine parts such as gaskets and intake manifold.

The cooling system is held under pressure while under operation, between 13-15 psi (pounds per square inch.) This additional pressure helps the coolant gain additional boiling point temperatures at a rate of one degree for every two pounds of pressure. For example; when a cooling system is held at 18 pounds of pressure it raises the boiling point by 9 degrees. Always check the radiator coolant level when the engine is cold. Visit - Cooling system flush Visit - Engine Coolant Visit - Coolant leak


Adding Coolant


Step 2 - Water Pump

The water pump is a mechanical pump that circulates the engine coolant throughout the radiator and into the engine block and cylinder head(s) which is driven by an serpentine or timing belt or by the timing chain. 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 worse problem. If a failing or failed water pump is allowed to operate it can cause the engine to overheat or completely fail. A water pump is comprised of a main housing body, flange, main shaft, bearings, impeller, seals and a gasket to seal in against the engine block. When engine RPM increase so does the water pump flow rate. A water pump will typical last between 50,000 and 80,000 miles. When replacing a water pump always insist on high quality replacement parts to avoid a premature failure. Visit - Water pump replacement


Water Pump (Serpentine Belt Removed)


Step 3 - Cooling Thermostat

A thermostat is a temperature sensitive device located in the thermostat housing. The thermostat housing is located at the engine, in either the upper or lower hose connections. This thermostat restricts the coolant from the radiator until the engine has reach operating temperature which is about 195°. This allows for the engine to be run at specific temperatures to optimize the performance and emissions levels. When a thermostat sticks closed, it will cause the engine to overheat quickly, usually within 5 to 15 minutes of engine operation. Visit - Thermostat test

Step 4 - Radiator

A radiator is used to transfer heat from the engine coolant to the outside atmosphere via the cooling fins of the radiator. When air is forced through these fins either with the assistance of the cooling fan or the vehicles forward motion it lowers the temperature of the coolant which is then moved to the engine to re-start the cycle of heating and cooling. The amount of heat transferred from the coolant depends on the surface area of the radiator core. Automatic transmission vehicles, utilize a fluid cooler inside the radiator. 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, coolant is returned to the radiator through suction. Most radiators are made of an aluminum core, and plastic side tanks. Visit - Radiator replacement

Step 5 - Cooling Fan

The cooling fan is located directly behind the radiator and is used to pull air through the radiator at lower vehicle speeds to keep the engine from overheating. Cooling fans can either be mechanical which are belt driven, or electric, mounted on the radiator and temperature or utility controlled. Visit - Electric cooling fan replacement

A radiator cooling fan is powered by either the engine, or by an electric motor. When a cooling fan fails, it causes the coolant to retain heat, forcing the engine to run hot and eventually overheat. Cooling fans that is powered by the engine are engaged and disengaged by operating temperature which is controlled by a fan clutch. Visit - Fan clutch


Radiator Cooling Fans


Step 6 - Coolant Hoses

Engine coolant is transferred to various sections of the cooling system via cooling hoses. These hoses are double-walled nylon reinforced pre-molded units capable of withstanding high temperatures while enduring engine vibrations. Part of a routine maintenance schedule should be the inspection of the cooling system hoses. When inspecting these hoses there are a few things to look for that would warrant replacement: oil saturation, cracks, abrasions, seepage and clamp tightness. Visit - Coolant leaks.


Radiator Hose


Step 7 - Serpentine Belt

A serpentine belt is used to transfer energy from the engine to the cooling fan on clutch fan style of cooling fans. This belt must be maintained for the fan to operate properly. Visit - Serpentine belt replacement


Removing Serpentine Belt


Helpful Information

The engine's combustion chamber can reach temperatures of up over four thousand degrees Fahrenheit. About thirty percent of the fuel is converted into actual power, and the remaining seventy percent is developed 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 which is controlled by the thermostat. Car manufacturers have found that a 195° thermostat is optimum for efficiency. Below this threshold the catalytic converter will not work properly which will produce increased emissions.

In the beginning, water was used for cooling systems, as it's the most efficient fluid to absorb and dissipate heat. The disadvantage of using water is that it freezes at a higher temperature and, boils at a lower temperature than coolant besides causing rust. Eventually, water was mixed with ethylene glycol, which worked as an anti-freeze agent, it also increased the boiling point of the mixture. Low levels of coolant can lead to problems related to engine overheating.

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AUTHOR


Written by
Co-Founder and CEO of 2CarPros.com
35 years in the automotive repair field, ASE Master Technician, Advanced Electrical and Mechanical Theory.


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Article first published (Updated 2013-11-19)