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Chapter: Mechanical : Automobile Engineering : Vehicle Structure and Engines

Engine Support Cooling system

The cooling system removes excess heat to keep the inside of the engine at an efficient temperature. · Air Cooling · Liquid Cooling · Water cooling Coolant. Water Jackets:


Cooling system:


The cooling system removes excess heat to keep the inside of the engine at an efficient temperature.


·      Air Cooling

·      Liquid Cooling


·      Water cooling Coolant. Water Jackets:


Water Jackets Surrounds the cylinders with water passage. Absorbs heat from the cylinder wall. Pump move water to radiator where heat is exchanged to the air. 66


Coolant Flow:


Coolant flows through the water jackets where it absorbs heat. It then flows through the radiator where heat is transferred to the air passing through. The amount of flow is determined by the water pump. The flow direction is controlled by the thermostat.

Warm Engine:


The thermostat opens when the engine warms up. This allows coolant to circulate through the radiator and the water jackets.


Cold Engine:


When an engine is cold, the thermostat is cold. Coolant flow is through the bypass hose and the water jackets. This allows the engine to warm up evenly.


Coolant :

·        Coolant Water (Boiling Point 100° C)

·        Glycerin (Boiling Point 290 ° C)

·        Ethylene glycol (Boiling Point 197 ° C)

·        Antifreeze (methyl alcohol, ethyl alcohol )


Cooling System:


·        Water pump is driven by the crankshaft through Timing Belt ( Keeps Cam and Crank shafts in time)


·        Drive/accessory Belt (Runs alternator, power-steering pump, AC, etc.) Serpentine Belt V-Belt

·        Electric fan is mounted on the radiator and is operated by battery power. It is controlled by the thermostat switch.



Need for cooling system

The cooling  system  has  four  primary  functions. These functions are as follows:


1.          Remove excess heat from the engine.

2.   Maintain  a  constant  engine  operating temperature.


3.          Increase the temperature of a cold engine as quickly as possible.

4.          Provide a means for heater operation (warming the passenger compartment).


Types of cooling system:


The different Types of cooling system are

1.          Air cooling system

2.          Liquid cooling system

3.          Forced circulation system


4.          Pressure cooling system


Air-Cooled  System :


The simplest type of cooling is the air-cooled, or direct, method in which the heat is drawn off by moving air in direct contact with the engine Several fundamental principles of cooling are embodied in this type of engine cooling. The rate of the cooling is dependent upon the following:


1.          The area exposed to the cooling medium.

2.          The heat conductivity of the metal used &

the volume of the metal or its size in cross section .

3.          The amount of air flowing over the heated surfaces.


4.          The difference in temperature between the exposed metal surfaces and the cooling air.


Liquid-cooled  system;


Nearly all multi cylinder engines used in automotive, construction, and material-handling equipment use a liquid-cooled system. Any liquid used in this type of system is called a COOLANT.


A simple liquid-cooled system consists of a radiator, coolant pump, piping, fan, thermostat, and a system of water jackets and passages in the cylinder head and block through which the coolant circulates. Some vehicles are equipped with a coolant distribution tube inside the cooling passages that directs additional coolant to the points where temperatures are highest.


Cooling of the engine parts is accomplished by keeping the coolant circulating and in contact with the metal surfaces to be cooled. The operation of a liquid- cooled system is as follows:


The pump draws the coolant from the bottom of the radiator, forcing the coolant through the water jackets and passages, and ejects it into the upper radiator tank. The coolant then passes through a set of tubes to the bottom of the radiator from which the cooling cycle begins.

The radiator is situated in front of a fan that is driven either by the water pump or an electric motor. The fan ensures airflow through the radiator at times when there is no vehicle motion. The downward flow of coolant through the radiator creates what is known as a thermosiphon action. This simply means that as the coolant is heated in the jackets of the engine, it expands. As it expands, it becomes less dense and therefore lighter. This causes it to flow out of the top outlet of the engine and into the top tank of the radiator. As the coolant is cooled in the radiator, it again becomes more dense and heavier. This causes the coolant to settle to the bottom tank of the radiator.


The heating in the engine and the cooling in the radiator therefore create a natural circulation that aids the water pump. The amount of engine heat that must be removed by the cooling system is much greater than is generally realized. To handle this heat load, it may be necessary for the cooling system in some engine to circulate 4,000 to 10,000 gallons of coolant per hour. The water passages, the size of the pump and radiator, and other details are so designed as to maintain the working parts of the engine at the most efficient temperature within the limitation imposed by the coolant.



Pressure cooling system


Radiator Pressure Cap


The radiator pressure cap is used on nearly all of the modern engines. The radiator cap locks onto the radiator tank filler neck Rubber or metal seals make the cap-to-neck joint airtight. The functions of the pressure cap are as follows:

1.     Seals the top of the radiator tiller neck to prevent leakage.

2. Pressurizes system to raise boiling point of coolant.

3. Relieves excess pressure to protect against system damage.

4. In a closed system, it allows coolant flow into and from the coolant reservoir.


The radiator cap pressure valve consists of a spring- loaded disc that contacts the filler neck. The spring pushes the valve into the neck to form a seal. Under pressure, the boiling point of water increases. Normally water boils at 212°F.


However, for every pound of pressure increase, the boiling point goes up 3°F. Typical radiator cap pressure is 12 to 16 psi. This raises the boiling point of the engine coolant to about 250°F to 260°F. Many surfaces inside the water jackets can be above 212°F. If the engine overheats and the pressure exceeds the cap rating, the pressure valve opens. Excess pressure forces coolant out of the overflow tube and into the reservoir or onto the ground.


This prevents high pressure from rupturing the radiator, gaskets, seals, or hoses. The radiator cap vacuum valve opens to allow reverse flow back into the radiator when the coolant temperature drops after engine operation. It is a smaller valve located in the center, bottom of the cap.


The cooling and contraction of the coolant and air in the system could decrease coolant volume and pressure. Outside atmospheric pressure could then crush inward on the hoses and radiator. Without a cap vacuum or vent valve, the radiator hose and radiator could collapse.


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