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
manufacturers 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
1-35