LO 11-2 Identify and explain the purposes and functions of the cooling system

LO 11-02: Identify and explain the purposes and functions of the cooling system.

Removing Excess Heat

The flame temperature of diesel fuel is approximately 3900° F (2149° C). Under pressure, the heat of combustion momentarily but regularly exceeds this temperature. Sustained operation of the engine at temperatures like this without some means to remove the heat would quickly result in damaged and destroyed engine components. Operating clearances between moving engine parts would disappear and cause engine seizure. Components such as pistons and valves would burn or soften and would become permanently distorted under the high temperatures. Lubrication oil would also burn upon contact with hot engine components. The oil viscosity would also become too thin to properly support bearing loads and lubricate parts.

Some combustion heat is radiated by hot engine surfaces and removed by air circulation in the engine compartment. A significant amount of heat is also emitted by the exhaust system. However, to prevent engine damage caused by the transfer of heat into engine components, cooling system coolant absorbs heat to enable its transfer from the engine to the atmosphere through the radiator Figure 4. Some of the coolant heat is repurposed to warm up passenger compartments, which is a particularly important function on buses.

FIGURE 11-4: Cooling system components and coolant circulation patterns through a typical 16 L, HD diesel engine.

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