TM 1-1510-223-10 Table 2-1.  Engine Fire Extinguisher Gage Pressure TEMP °C -40 -29 -18 -06 04 16 27 38 48 190 220 250 290 340 390 455 525 605 PSI to to to to to to to to to 240 275 315 365 420 480 550 635 730 BTO0194 propeller operation, 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.    These oil cooler units are the only airframe mounted part of the oil   system   and   are   located   in   the   lower   aft   nacelles below     the     engine     air     intake.          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 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. 2-13).    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 threeposition toggle switches, placarded # 1 or # 2 ENG START, are located on the overhead control panel (fig. 2-13).    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. 2-7). 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.  2-13), 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.        2-13),    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.  2-7). 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 # l 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.  2-7). 2-33