TM 1-1510-224-10 propeller    operation    and    lubrication    of    the    reduction gearbox  and  engine  bearings  is  supplied  by  an  external line  from  the  high  pressure  pump.    Two  scavenge  lines return    oil    to    the    tank    from    the    propeller    reduction gearbox.  A noncongealing, external oil cooler keeps the engine   oil   temperature   within   operating   limits.      The capacity of each engine oil tank is 2.5  U.S. gallons.  The total system capacity for each engine, which includes the oil  tank,  oil  cooler,  lines,  etc.,  is  approximately  3.5  U.S. gallons.    The  oil  level  is  indicated  by  a  dipstick  attached to   the   oil   filler   cap.      Oil   grade,   specifications,   and servicing points are described in Section XII, Servicing. b.   The  oil  system  of  each  engine  is  coupled  to an  oil  cooler  unit  (radiator)  of  fin-and-tube  design.    The oil  cooler  unit,  located  in  the  lower  aft  nacelle  below  the engine  air  intake,  is  the  only  airframe  mounted  part  of the  oil  system.    Each  oil  cooler  incorporates  a  thermal bypass   valve   which   assists   in   maintaining   oil   at   the proper temperature range for engine operation. 2-28.  ENGINE IGNITION SYSTEM. a.    Description.     The  basic  ignition  system  for each engine consists of a solid state ignition exciter unit, two   igniter   plugs,   two   shielded   ignition   cables,   pilot controlled   ignition   and   engine   start   switches,   and   the auto  ignition  switches  (fig.  2-15).    Placing  either    ENG START switch to  START - IGNITION position will cause the respective engine to motor and igniter plugs to spark, igniting  the  fuel/air  mixture  sprayed  into  the  combustion chamber  by  the  fuel  nozzles.    The  ignition  system  is activated  for  ground  and  air  starts,  but  is  switched  off after combustion light up. b.    Ignition  and  Engine  Starter  Switches.    Two three-position toggle switches, placarded  #1 or   #2  ENG START, are located on the overhead control panel (fig.  2-15).    These  switches  will  initiate  starter  motoring and  ignition  in  the   START   IGNITION   position,   or   will motor the engine in the  STARTER ONLY position.  The START IGNITION  switch  position  completes  the  starter circuit  for  engine  rotation,  energizes  the  igniter  plugs  for fuel combustion, and activates the respective #1 IGN ON or #2 IGN ON annunciator on the annunciator panel.  In the  center  position  the  switch  is  OFF.    Two  5-ampere circuit  breakers  on  the  overhead  circuit  breaker  panel, placarded  IGNITOR CONTR  #1  and  #2,  protect  ignition circuits.  Two 5-ampere circuit breakers on the overhead circuit breaker panel, placarded  START CONTR #1  and #2, protect starter control circuits (fig. 2-9). 2-29.  AUTO IGNITION SYSTEM. If  armed,  the  auto  ignition  system  automatically energizes  both  igniter  plugs  of  either  engine,  should  an accidental  flameout  occur.    The  system  is  not  essential to  normal  engine  operation,  but  is  used  to  reduce  the possibility of power loss due to icing or other conditions. Each  engine  has  a  separate  auto  ignition  control  switch (fig.  2-15)  and  a  green  annunciator,  placarded    #1  IGN ON or   #2   IGN   ON,   on   the   annunciator   panel.      Auto ignition is accomplished by energizing both igniter plugs in each engine. NOTE The   system   should   be   turned   OFF during  extended  ground  operation  to prolong the life of the igniter plugs. a.  Auto Ignition Switches.  Two switches located on the overhead control panel (fig. 2-15), each placarded -AUTO    IGNITION    -    ARM,    control    the    auto    ignition systems.    The  ARM  position  initiates  a  readiness  mode for the auto ignition system of the corresponding engine. The  system  is  disarmed  when  in  the  off  position.    Each circuit is protected by the corresponding  START CONTR #1   or   #2,   5-ampere   circuit   breaker   on   the   overhead circuit breaker panel (fig. 2-9). b.  Auto Ignition Annunciators.  If an armed auto ignition  system  changes  from  a  ready  condition  to  an operating  condition  (energizing  the  igniter  plugs  in  the engine)   the   corresponding   engine's   green   annunciator will illuminate.  The annunciator is placarded  #1 IGN ON or    #2   IGN   ON    and    indicates    that    the    igniters    are energized.    The  auto  ignition  system  is  triggered  from  a ready  condition  to  an  operating  condition  when  engine torque   drops   below   approximately   20%.      Therefore, when  an  auto  ignition  system  is  armed,  the  igniters  will be   energized   continuously   during   the   time   when   an engine  is  operating  at  a  level  below  approximately  20% torque.    The  auto  ignition  annunciators  are  protected  by the    5-ampere    IGNITOR    CONTR    #1    or     #2    circuit breakers,  located  on  the  overhead  circuit  breaker  panel (fig. 2-9). 2-30.  ENGINE STARTER-GENERATORS. One starter-generator is mounted on the accessory  drive  section  of  each  engine.    Each  starter- generator  is  able  to  function  either  as  a  starter  or  as  a generator.        In    the    starter-function,    28    volts    DC    is required  to  power  rotation.    In  the  generator  function, each  unit  is  capable  of  400  amperes  DC  output.    When the starting function is selected, the starter control circuit receives power through the respective 5-ampere  START CONTR  circuit  breaker  on  the  overhead  circuit  breaker panel   (fig.   2-9),   from   either   the   aircraft   battery   or   an external  power  source.    When  the  generating  function  is selected, the starter-generator provides electrical power. 2-31.  ENGINE INSTRUMENTS. The  engine  instruments  are  arranged  vertically near the center of the instrument panel (fig. 2-18). 2-39