Page 173 - 05. Subyek Teknik Mesin - Automobile Mechanical and Electrical Systems Automotive Technology Vehicle Maintenance and Repair (Vehicle Maintenance Repr Nv2) by Tom Denton

2
Engine systems 157

Water
Radiator Radiator inlet pump

Thermostat
Heater
tank

Radiator Heater Heater
outlet matrix valve Jiggle
valve

Figure 2.148 Basic cooling system

Figure 2.149 Water pump and its position in the engine block

The heat distribution within the engine needs to be controlled. The temperature
around all cylinders and combustion chambers should be identical. The heat
removed by the cooling system has, therefore, to be consistent for all areas of
the engine. All modern engines have a fairly rapid coolant circulation within the
engine so that an even temperature distribution is achieved.
The water (or coolant) pump draws the coolant through a radiator bypass
channel when the engine is cold and from the radiator when the engine is hot
( Fig. 2.149 ). The impeller on the water pump drives the coolant into the engine
coolant passages or water jacket. Water-jacket passages are carefully designed
to direct the coolant around the cylinders and upwards over and around the
combustion chambers.
The density of coolant falls as it heats up and, as the temperature approaches
boiling point, bubbles begin to form. These bubbles can create areas in the water Key fact
jacket where the coolant is at a lower density and the actual mass of coolant in
The density of coolant falls as it
those areas is reduced. The reduced mass of coolant therefore cannot effectively
heats up and, as the temperature
absorb heat effi ciently to cool the engine.
approaches boiling point, bubbles
To overcome this problem, all liquid cooling systems are pressurized. When begin to form.
hot, most modern systems have an operating pressure equivalent to about one
atmosphere (1 bar, or 100 kPa). The pressure is obtained by restricting the loss of