COOLING SYSTEM
A. Introduction
I.C Engines at best can transform about 25-30 % of the chemical energy from the fuel in to mechanical
energy.
About 35 % of the heat generated is lost to the cooling
medium remainder being dissipated through exhaust and lubricating oil.
z 1/3 Heat to Useful Work
z 1/3 Heat to cooling System
z 1/3 Heat to exhaust system
B. The Purpose of Cooling System
Prevent Overheating
z Excess Heat generated in engine
z Peak temperatures exceed melting point of metal
Regulate the most efficient Temperature
z Regulate Temperature
z Allow engine to warm up in cool weather
z Maintain engine in optimum range.
C. Consequence of engine running too hot:
Pre-ignition, Detonation/Knock
All result in very high pressure rise and possible damage to engine
Heat Fatigue of components
Burnt Pistons
Burnt Valves
Failure of lubrication system
Oil breakdown
Oil film at cylinder destroyed at 200C
o Scoring of piston & sleeves
Warping & fracture of components
D. Consequence of Engine Running Too Cold:
Unnecessary Wear
Poor Fuel Economy
Incomplete Combustion
Lower coolant Temperature
o More energy transferred out of cylinder
o Energy from is wasted & not available for work (Power)
Promotes corrosive conditions in engine
Water of combustion reacts with sulfur oxides in exhaust
o Forms acids
Allows water & sludge to accumulate in crankcase
Over time, fuel diluting the oil will accumulate
o Normally lighter volatile fuel will evaporate as temp. rises
E. Characteristics of an efficient cooling system
The two main characteristics desired of an efficient cooling
system are:
It should capable of removing about 30 % of the heat generated in the combustion chamber
while maintaining the optimum temperature of the engine under all operating conditions of
the engine
It should remove heat at a faster rate when engine is hot. However during starting of the
engine the cooling should be minimum, so that the working parts of the engine reach their
operating temperatures in a short time
Parts of Engine Cooling System
Cold Engine
When an engine is cold, the thermostart is cold.
Coolant flow is through the bypass hose and the water jackets.
This allows the engine to warm up evenly.
The thermostat should start to open at 77 oC and fully open at 85oC
Warm Engine
The thermostat opens
when the engine warms up.
This allows coolant to circulate through the radiator and the water jackets.
Water Jackets
Defined as the open space within in the cylinder block and cylinder head
where coolant flows
Water jackets are designed to allow coolant flow to the right spots flow
to the right spots so that maximum cooling can be obtained
Water Pump
It purpose is to circulate the water through the cooling system
Located on the front part of the engine
In most of the vehicles it is driven by a belt is attached to the crankshaft
crankshaft
As the crankshaft turns the fan belt turns
Thermostat
One of the most important parts of the cooling system
Its purpose is to keep the engine coolant at most pppg efficient
temperature
The thermostat is used to bring thecoolant temperature up to operating
as quickly as possible
It is designed to sense the temperature of the coolant
Radiator
Its purpose is to allow fresh air reduce the temperature of the coolant.
As the coolant passes through the tubes air is forced around the tube
This causes a transfer of heat from the hot coolant to the cooler air.
In this case, heat is exchanged from the liquid coolant to air. This is
called a liquid-to air heat exchanger
Coolant flows through the air fins
The fins and tubes are cooled core
Radiator Pressure Cap
Pressure caps are designed to
Increase the pressure on the cooling system
Reduce cavitations
Protecting the radiator hose
Prevent or reduce surging
It is important to put pressure on the cooling system. Radiator pressure
caps are typically near 15 psi
As the pressure increases the boiling point of the coolant also increases
(about 3 degrees for each 1 psi increase)
Pressure Cap
Expansion tank
Fan
Coolant Temperature Indicator
