TM 10-3930-664-24 e. The  fuel  system  is  designed  to  use  fuel  to  cool  and  lubricate  the  injection  pump  and  injectors.    Fuel  is continually vented from the injection pump and a small amount of fuel leaks by the injector needle valve during injection. Any leakage past the needle valve enters the fuel drain manifold, which routes fuel back into the fuel tank. f. The  fuel/water  separator  is  equipped  with  a  valve  which  can  be  opened  regularly  to  drain  collected  water. Regular  maintenance,  including  draining  moisture  from  the  fuel/water  separator  and  supply  tanks,  is  essential  to  keep water out of the fuel. g. The  Lucas  CAV  DPA  fuel  injection  pump  is  a  rotary  distributor  pump.    The  pump  uses  a  coded  spring connection to change the governor setting.  The amount of fuel injected and subsequently the speed and power from the engine is controlled by the fuel control lever. h. The injection pump idle adjustment screw provides a stop for the lever at low speed.  The screw can be used to increase idle speed for accessory loading or, if required, to lower idle speed.  The pump is equipped with a mechanical shut down lever.  This lever is spring-loaded in the run position. i. Engine Cooling System.  The function of the engine cooling system (Figure 1-8) is to maintain a specified operating temperature for the engine.  Heat generated by the engine is absorbed by coolant flowing through passages in the cylinder block and cylinder head. j. Heat  is  removed  from  the  coolant  as  it  flows  through  the  radiator.    The  high  temperature  engine  coolant circulates through tubes in the radiator, while cool air is blown across the tubes by the  cooling  fan.    The  resulting  lower temperature coolant is drawn from the radiator to the engine by an integrally mounted water pump. k. The  water  pump  empties  coolant  into  the  coil  cooler  cavity  of  the  cylinder  block.    The  coolant  circulates around each cylinder and crosses the block to the fuel pump side of the engine.  The coolant flows up  into  the  cylinder head and crosses over the valve bridges.  As the  coolant  flows  across  the  head  it  provides  cooling  for  injector  nozzles. The coolant passes down the exhaust manifold side of the engine to the integral thermostat housing. l. When the engine is below operating temperature, the thermostat is closed, and the coolant flow bypasses the radiator and goes to the water pump inlet via internal drillings in the block and cylinder head.  When operating temperature is reached, the thermostat opens, blocking the bypass passage to the water pump and opening the outlet to the radiator. m. The water pump is belt driven from the crankshaft pulley.  An automatic belt tensioner is used to prevent the belt from slipping on the pump pulley. n. Air  System.    The  engine  air  system  consists  of  two  air  cleaners/filters,  air  inlet  hose,  intake  manifold,  and exhaust manifold (refer to Figure 1-2 for component location). o. Intake air flows directly from the air cleaner to the intake manifold.  From the intake manifold, air is pulled into the cylinder and used for combustion.  After combustion it is forced out of the cylinders through the exhaust manifold. 1-26