one shown in figure 5-5, which provides a large volume
shroud that improves fan efficiency by assuring that all
capacity and is nonpositive in displacement. This type
the air handled by the fan passes through the radiator.
of pump has an impeller with blades that force the
Fan blades are spaced at intervals around the fan
coolant outward as the impeller rotates. The shaft on
hub to aid in controlling vibration and noise. They are
which the impeller is mounted is usually driven by a
often curled at the tip to increase their ability to move
fan belt and revolves in a bushing or in ball bearings
air. Except for differences in location around the hub,
inside the housing, as shown in the illustration. Also
most blades have the same pitch and angularity.
shown in the illustration is the nonadjustable seal
Bent fan blades are very common and result in
a s s e m b l y, w h i c h p r eve n t s l e a k a g e a r o u n d t h e
noise, vibration, and excess wear on the water pump
externally driven water pump shaft. For different
c o o l i n g s y s t e m s , p u m p s va r y c o n s i d e r a b l y i n
shaft. You should make it a practice to visually inspect
construction of seals, bearings, mounting, and drive.
the fan blades, pulleys, pump shaft endplay, and drive
belts at every preventive maintenance inspection.
Fan and Shroud
At 300 rpm, an 18-inch fan will consume over 2 hp.
This power drain increases rapidly with an increase in
The engine fan is usually mounted on the end of the
engine speed. Since the fan is required primarily at low
water pump shaft and is driven by the same belt that
engine speeds, couplings have been devised that
drives the pump. The fan pulls a large volume of air
disconnect the fan above certain speeds.
through the radiator core, which cools the hot water
circulating through the radiator. In addition to
The fan drive clutch is a fluid coupling that
removing heat from the water in the radiator, the flow
contains silicone oil. Fan speed is controlled by the
of air created by the fan causes some direct cooling of
torque-carrying capacity of the oil. The more silicone
the engine itself. Some engines are equipped with a
oil in the coupling, the greater the fan speed; the less
silicone oil, the slower the fan speed.
Two types of fan drive clutch controls are in use
today. One type uses a bimetallic strip and control
piston in the front of the fluid coupling. The bimetallic
strip bows outward with an increase in surrounding
temperature and allows the piston to move outward.
The piston opens a valve that regulates the flow of
silicone oil into the coupling from a reserve chamber.
When the valve is closed, the oil is returned to the
reserve chamber through a bleed hole.
The bimetallic, spring-type, fan drive clutch uses a
spring connected to an opening plate. This produces an
action much the same as the bimetallic strip type of
control. Both types of controls cause the fan speed to
increase with a rise in temperature and to decrease as
the temperature goes down.
The water passages in the cylinder block and
cylinder head form the engine water jacket. (See figure
5-2.) In the cylinder block, the water jacket completely
surrounds all cylinders along their full length. Within
the jacket, narrow passages are provided between the
A. Pulley and hub assembly
F. Seal assembly
B. Bearing retainer
cylinders for coolant circulation around them. In
C. Shaft and bearing assembly
H. Plate gasket
addition, water passages are provided around the valve
seats and other hot parts of the cylinder block. In the
E. Seal washer
cylinder head, the water jacket covers the combustion
Figure 5-5.--Water pump.
chambers at the top of the cylinders and contains