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 1-35