CHAPTER 6 COOLING AND LUBRICATING SYSTEMS

LEARNING OBJECTIVE: Explain the relationship of the cooling system to engine operation. Identify design and functional features of individual cooling system components. Identify maintenance procedures applicable to cooling systems. Identify types of lubrication systems and explain their operational charactetistics and maintenance requirements.

All internal combustion engines are equipped with cooling and lubricating systems that work in conjunction with each other to promote efficient engine operation and performance. The cooling and lubricating systems discussed in this chapter, along with their respective components and maintenance requirements, are representative of the types of systems you will be expected to maintain.

Because of the variety of engines used, there are differences in the applications of features of their cooling and lubricating systems. Keep in mind that maintenance procedures and operational characteristics vary from engine to engine; therefore, always refer to the manufacturer's service manuals for specific information

ENGINE COOLING SYSTEMS

LEARNING OBJECTIVE: Explain the relationship of the cooling system to engine operation. Identify, design and functional features of individual cooling system components. Identify maintenance procedures applicable to cooling systems.

An internal combustion engine produces power by burning fuel within the cylinders; therefore, it is often referred to as a "heat engine." However, only about 25% of the heat is converted to useful power. What happens to the remaining 75 percent? Thirty to thirty five percent of the heat produced in the combustion chambers by the burning fuel are dissipated by the cooling system along with the lubrication and fuel systems. Forty to forty-five percent of the heat produced passes out with the exhaust gases. If this heat were not removed quickly, overheating and extensive damage would result. Valves would burn and warp, lubricating oil would break down, pistons and bearing would overheat and seize, and the engine would soon stop.

The necessity for cooling may be emphasized by considering the total heat developed by an ordinary six- cylinder engine. It is estimated that such an engine operating at ordinary speeds generates enough heat to warm a six-room house in freezing weather. Also, peak combustion temperatures in a gasoline engine may reach as high as 4500F, while that of a diesel engine may approach 6000F. The valves, pistons, cylinder walls, and cylinder head, all of which must be provided some means of cooling to avoid excessive temperatures, absorb some of this heat. Even though heated gases may reach high temperatures, the cylinder wall temperatures must not be allowed to rise above 400F to 500F. Temperatures above this result in serious damage as already indicated. However, for the best thermal efficiency, it is desirable to operate the engine at temperatures closely approximating the limits imposed by the lubricating oil properties.

The cooling system has four primary functions. These functions are as follows:

1. Remove excess heat from the engine.

2. Maintain a constant engine operating temperature.

3. Increase the temperature of a cold engine as quickly as possible.

4. Provide a means for heater operation (warming the passenger compartment).

Air is continually present in large enough quantities to cool a running engine; therefore, vehicle engines are designed to dissipate their heat into the air through which a vehicle passes. This action is accomplished either by direct air-cooling or indirectly by liquid cooling. In this chapter we will be concerned with both