Page 167 - 05. Subyek Teknik Mesin - Automobile Mechanical and Electrical Systems Automotive Technology Vehicle Maintenance and Repair (Vehicle Maintenance Repr Nv2) by Tom Denton

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Engine systems 151

2.3 Engine cooling

2.3.1 Introduction

Heat is a form of energy that can be sensed by a change in temperature. The
engine uses chemical energy in the fuel and converts it into heat and then into
movement. The energy conversion process in an engine is not very effi cient and
only about 30% is converted into movement energy. Of the remaining heat, up
to 50% goes out of the exhaust and the rest heats the engine. Excessive heating
of the engine must be controlled to prevent damage. Components expand
with heat and, at high temperatures, this expansion can cause seizure, and
burning of pistons and valve seats. High temperature would also produce rapid
deterioration of the engine oil.
Cooling systems are designed to maintain engines at an optimum temperature.
This allows the design of components that expand on heating to form very
tight fi ts and running tolerances. The adjustment of ignition and fuel settings Key fact
is equated to the optimum temperature required for the clean and effi cient Cooling systems are designed to
combustion of fuel. Because a cold engine produces high levels of unwanted maintain engines at an optimum
exhaust emissions, a rapid warm-up is needed to keep emissions to a minimum. temperature.
The ‘normal’ running engine coolant temperature is maintained at about the
boiling point of water, which enables effi cient combustion. A further reduction
in harmful exhaust emissions is achieved by keeping the warm-up time to a
minimum. There are two types of cooling system.
Air-cooled systems have the air stream passing directly over the cylinder heads
and cylinders to remove heat from the source ( Fig. 2.137 ). Fins are cast into the
cylinder heads and cylinders to increase the surface area of the components,
thus ensuring that suffi cient heat is lost.
Liquid-cooling systems use a coolant to carry heat out of the engine and
dissipate the heat into the passing air stream ( Fig. 2.138 ). The liquid coolant is

contained in a closed system and is made to circulate almost continuously by the
impeller on the water pump. Heat is collected in the engine and dissipated from
the radiator into the passing air stream. Almost all modern cars and light vehicles
use liquid cooling systems.

2.3.2 System operation

The coolant is a mixture of water, antifreeze and inhibitors. The antifreeze is
usually ethylene glycol, which needs inhibitors to prevent corrosion and foaming.
These inhibitors have a lifespan of about two years, which means that the

Figure 2.136 Elements of a radiator; a key component in the cooling system