Fan and Shroud

The engine fan is usually mounted on the end of the water pump shaft and is driven by the same belt that drives the pump. The fan pulls a large volume of air through the radiator core that cools the hot water circulating through the radiator. In addition to removing the heat from the water in the radiator, the flow of air created by the fan causes some direct cooling of the engine itself. On some construction equipment, such as dozers and track loaders, the fan blows air through the radiator vice pulling the air. Besides cooling the water, the blowing of air keeps sand, dirt, and debris out of the radiator. Some engines are equipped with a shroud that improves fan efficiency by assuring that all the air handled by the fan passes through the radiator.

Fan blades are spaced at intervals around the fan hub to aid in controlling vibration and noise. They are often curled at the tip to increase their ability to move air. Except for differences in location around the hub, most blades have the same pitch and angularity.

Bent fan blades are a common problem. They cause noise, vibration, and excess wear on the water pump shaft. Visual inspection of the fan blades, pulleys, pump shaft end play, and drive belts are part of your pre- and post-operational checks. A bent or distorted fan or one with a loose blade should be replaced. When the fan is merely loose on its mounting, tightening is in order. Loose fan belts can be adjusted for proper tension, usually by adjusting the generator or alternator on its mounting (fig. 1-47). A common method for measuring belt tension is to press down on the belt at a point midway between the generator or alternator and the fan pulley, and measure the amount of deflection. The amount of deflection varies and should be set to the manufacturer's specification. A rule of thumb used in the NCF for belt tension is no more than a one-half inch deflection.

Water Jacket

The water passages in the cylinder block and cylinder head form the engine water jacket. The passages of the water jacket are designed to control circulation of coolant and provide proper cooling throughout the engine. In the cylinder block, the water jacket completely surrounds all cylinders along their full length. Water passages are also provided around the valve seats and hot parts of the cylinder block. In the cylinder head, the water jacket covers the combustion chambers at the top of the cylinders and contains

Figure 1-47.-Drive belt adjustment.

passages around the valve seats when the valves are located in the head.

Thermostat

Automatic control of the temperature of an engine is necessary for efficient engine performance and economical operation. Since all engine parts are in a contracted state when cold, the engine temperature should be brought to normal as quickly as possible. The water pump starts coolant circulating the moment the engine is started, which is undesirable during cold weather operations. Coolant circulation is restricted by the installation of a thermostatically controlled valve, or thermostat, in the cylinder head water outlet. This valve allows coolant to circulate freely only within the block until the desired temperature is reached. This shortens the warm-up period. A bypass is used to direct the water

Figure 1-48.-Thermostat operation.

from the block to the pump when the passage to the radiator is blocked by the closed thermostat (fig. 1-48).

Some stationary engines and large trucks are equipped with shutters that supplement the action of the thermostat in providing a faster warmup and in maintaining proper operating temperatures. When the engine coolant is below a predetermined temperature, between 185F to 195F, the shutters, located in front of the radiator, remain closed and restrict the flow of air through the radiator. Then, as the coolant reaches proper temperature, the shutters start to open.

Overflow Tank

The overflow tank serves as a receptacle for coolant forced out of the radiator overflow pipe and provides for its return to the system. As the engine cools, the balancing of pressures causes the coolant to siphon back into the radiator.

Cooling systems using an overflow tank are known as closed cooling systems (fig. 1-49). Coolant is usually added to this system through the overflow tank that is marked for proper coolant level. NEVER remove the radiator cap located on the radiator unless you are

positive the system is cold. If there is any pressure in the radiator, it will spray you with hot steam and coolant. Use extreme caution when performing operator's maintenance on a closed cooling system.

Expansion Tank

Some engines use an expansion tank in their cooling system (fig. 1-50). The tank is mounted in series with the upper radiator hose and is used to supply extra room for coolant expansion and generally takes the place of the upper radiator tank. The pressure cap and the overflow line are also mounted on the expansion tank.