ARMY TM 92815-252-24 AIR FORCE TO 38G1-92-2 CHAPTER 2 OPERATION Section I.  PRINCIPLES OF OPERATION 2-1.  INTRODUCTION. This section contains functional descriptions of the engine systems and how they are connected to the end item. 2-2.  COOLING SYSTEM. The cooling system consists of a radiator, hoses, thermostat, belt driven fan, water pump, and cooling jackets within the engine.  The water pump forces coolant through passages (coolant jackets) in the engine block and cylinder head where coolant absorbs heat from the engine.  When the coolant temperature is below operating temperature, the thermostat is closed  and  coolant  is  bypassed  to  the  water  pump  inlet.    As  coolant  temperature  increases  to  160°F  (71  C),  the thermostat starts to open, restricting bypass flow and opening flow to the radiator.  As coolant temperature continues to increase to 1850F (85°C), the thermostat is fully opened, shutting off all bypass flow and providing full flow through the radiator.  Air forced through the fins of the radiator by the fan cools the coolant pumped through the radiator.  Items are added to the engine to monitor coolant temperature and to warn if temperature exceeds a predetermined value. 2-3.  LUBRICATION SYSTEM. The lubrication system consists of an oil sump, dipstick, pump, relief valve, and filter.  The oil sump is a reservoir for lubricating  oil.    The  dipstick  indicates  oil  level  in  sump.    The  pump  draws  oil  from  the  sump  through  a  screen  which removes large impurities.  The oil then passes through a relief valve preset to limit oil pressure to 47 to 59 psi (324 to 407  kPa).    The  oil  then  passes  through  a  spin-on  type  filter  where  small  impurities  are  removed.    From  the  filter,  oil enters the cylinder head oil gallery and flows to the crankshaft and bearings.  The connecting rod bearings are pressure fed through internal drillings in the crankshaft from the supply to the main bearings.  Splash oil lubricates the gears, and the underside of the pistons.  The governor camshaft is lubricated by a drilled bolt/oil jet.  An internal crankcase drilling provides an oil feed to the hydraulic tappets.  After passing through the block, the oil returns to the oil sump.  Items are added to monitor oil pressure and to warn/stop engine if pressure drops to a dangerously low value. 2-4.  FUEL SYSTEM. 2-4.1.  The fuel system consists of an external fuel tank, electrically driven transfer pump, fuel filter/water separator, fuel filter, fuel injection pump and fuel injector for each cylinder, and piping.  Fuel from an external source is supplied to the fuel  injection  pumps.    The  injection  pumps  provide  a  pressurized  metered  quantity  of  clean  atomized  fuel  through  the injector nozzles into the cylinders at a precise time near the end of the compression stroke of each piston.  The fuel that is not used by the injectors is returned to the fuel tank via an excess fuel return line. 2-4.2.    Extremely  cold  outside  temperatures  make  starting  the  engine  difficult.    To  improve  engine  starting,  a  cold weather  starting  aid  has  been  provided  that  features  two  heater  plugs  in  the  intake  manifold.    The  heater  plugs  are energized during engine preheat starting cycle. 2-5.  ELECTRICAL SYSTEM. The electrical system consists of external mounted batteries, starter, battery charging alternator, and related relays and switches for control of the system.  Battery power supplied to the starter during the start cycle energizes the starter which engages  the  ring  gear  of  the  flywheel  causing  the  engine  to  turn  over.    When  engine  start  is  complete,  the  starter  is deenergized and disengages from the flywheel. 2-1