ARMY TM 9-2815-254-24 AIR FORCE TO 38G1-94-2 CHAPTER  2 OPERATION SECTION  I.  PRINCIPLES  OF  OPERATION 2-1. INTRODUCTIONS 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  tem- perature, the thermostat is closed and coolant is bypassed to the water pump inlet. As coolant temperature in- creases  to  180°F  (82°C),  the  thermostat  starts  to  open,  restricting  bypass  flow  and  opening  flow  to  the  radiator.  As coolant temperature continues to increase to 203°F (95°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 pan, dipstick, pump, 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 spin-on type filter where small impurities are removed. From the filter, oil enters the cylinder head oil gallery and is distributed to the engines internal moving parts and to the fuel injection  pump.  After  passing  through  the  block  and  pump,  the  oil  returns  to  the  oil  sump.  Items  are  added  to  moni- tor 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, transfer pump, fuel filter/water separator, fuel injection pump, fuel injectors, and piping. Fuel from an external source is supplied to the fuel injection pump. The injection pump provides a pressurized metered quantity of clean atomized fuel through the injector nozzles into the cylinder 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. 2-1