ENGINE COOLING SYSTEMS

In this chapter, we will primarily discuss closed cooling systems for internal-combustion engines. After reading the information in this chapter, you should recognize the purpose and function of an engine cooling system. You should also recognize the principal components of the basic cooling system design that is used in diesel engines. In the basic maintenance of engine cooling systems, you should understand the need for various chemical inhibitors and how they are used in an engine cooling system for the control of corrosion. A great amount of heat is generated within an engine during operation. The combustion process produces the greatest portion of this heat; compression of gases within the cylinders and friction between moving parts add to the total amount of heat developed within an engine. Since the temperature of combustion alone is about twice that at which iron melts, it is apparent that, without some means of dissipating heat, an engine could operate for only a very limited time.

When fuel burns in the cylinders of an engine, only about one-third of the heat energy from the fuel changes into mechanical energy and then leaves the engine in the form of brake horsepower (BHP). (Brake horsepower is a measure of the developed power of an engine in actual operation.) The rest of the heat shows up as unwanted heat in the form of (1) hot exhaust gases, (2) frictional heat from the rubbing surfaces, and (3) heating of the metal walls that form the combustion chamber, cylinder head, cylinder, and piston. The job of the cooling system is to remove the unwanted heat from these parts so that the following problems can be prevented:

1. Overheating and the resulting breakdown of the lubricating oil film that separates the rubbing surfaces of the engine

2. Overheating and the resulting loss of strength of the metal itself

3. Excessive stresses in or between the engine parts resulting from unequal temperatures

Unwanted heat is transferred through the mediums of water, lubricating oil, air, and fuel. The water of the closed cooling system removes the greatest portion (approximately one-fourth) of the unwanted heat generated by combustion. The balance of the heat is carried away from the engine by the lubricating oil, the fuel, and the air. If the heat lost through cooling could be turned into work by the engine, the output of the engine would be almost doubled. However, the loss of valuable heat is necessary for an engine to operate.