Page 179 - Mechanic Diesel - TT

MECHANIC DIESEL - CITS

2 Wax pallet type thermostat
This type of wax pellet is used like a heating element. When the temperature of the circulating water is below the
operating temperature, the spring holds the valve in the closed position and water is not able to reach the top tank
of the radiator from the engine. As the water reaches operating temperature the wax pellet expands and forces the
valve open against spring tension. Now water reaches the top tank of the radiator from the engine. In this situation
the bypass port remains closed by the valve.

Radiator pressur cap
increase the boiling point of water. In normal atmospheric conditions, water boils at 100°C. At the highest
altitude, atmospheric pressure is less and water boils at temperatures below 100°C. To increase the boiling point
temperature of water, the pressure of the cooling system has to be increased. This is achieved by sealing the
system with a pressure cap.
Cooling losses due to evaporation can also be reduced by using a pressure cap. This allows the engine to run at
higher temperatures resulting in higher engine efficiency. The pressure cap fits onto the filler neck portion above
the radiator tank. If the pressure increases by 15 PSI, the boiling point temperature increases by 113°C.
There are two valves in the pressure cap
i Pressure valve

ii Vacuum valve
Clean of water cooling system
Pressure Flushing: In this method, water and air are used with sufficient pressure through the compressor to
clean the cooling system. This method is done in two ways
i Straight flushing: To clean the cooling system, air and water are sent under pressure from the radiator to the
water pump and water jackets.
ii Reverse flushing: In this method, air and water are released from the outlet pipe of the radiator by removing
the thermostat valve.
It is sent into the water jacket with pressure.
Coolant, Types and Its properties

Coolant: Coolant (also called antifreeze) is a special fluid. It is made of either ethylene glycol or propylene and is
usually green, blue, or pink colour. It is used to reduce the temperature of a system by removing heat to control
or reduce heat.

Types of Coolant
There are many types of coolants that are used for different purposes.
1 Water: Often used to prevent corrosion and maintain temperature.
2 Ethylene Glycol Based: Commonly used in automotive applications, it is mixed with water to make antifreeze.

3 Propylene Glycol Based: It is similar to ethylene glycol, but less toxic, used in food processing and
environmental uses.

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CITS : Automotive - Mechanic Diesel - Lesson 47 - 56