TM  9-2328-387-24-l 1 2-31.    ENGINE   COOLING    TESTS These  engine   cooling   tests  may  be  run  any  time  you  think  you  have  an  engine   cooling problem  or  if you  were  sent  here  by  another   test  chain.    Just  follow  the  path,  answering   the questions.     Additional   information   and  notes  are  given  on  the  facing   page  when   necessary. Please  note  that  this  paragraph   is  NOT  for diagnoses   of problems   with  the  temperature sending   unit  or the  gauge. Once  you  are  sure  that  the  cooling   system   is OK,  run  the  instruments    test  in  paragraph   2-38 to find  out  if the  gauge  is OK. Fold-out   FP-7  contains   a functional   diagram   of the  engine   cooling   system.    This  page  may be  left open  for  reference   while  testing. The  engine   cooling   system  is  a pressure-type    cooling   system  with  thermostatic    control  of coolant   circulation.     The  cooling   system   dissipates   heat  generated   from  combustion   and maintains   the  engine   operating   temperature    at  its  most  efficient   level.    When  the  engine   is cold  and  the  thermostat   is  closed,   coolant   is  recirculated   through   the  water  pump  and engine.    As the  engine   coolant   reaches   215°F  (102”C),   the  thermostat   opens,   allowing coolant  to flow  through   the  radiator   before  returning   to  the  water  pump  and  engine.    Any  air or vapor  in the  cooling   system  will  be forced  to the  surge  tank  under  the  liquid   level  and leave  through   a vent  tube.    As  the  system   cools,  the  extra  coolant   in the  tank  will  be drawn back  to the  radiator.    Normally   a 50-50  mixture   of water  and  ethylene   glycol-based    antifreeze will  be  used.   The  fan  is  activated   when  coolant  temperature    reaches   approximately    220”  F (104°C).    A separate   oil  cooler  is  mounted   in front  of the  radiator.    This  cooler  is divided  into two  parts.   The  top  half  is for transmission    oil.   The  bottom  half  is  for  engine   oil.   When  the cooling   system  pressure   reaches   approximately    15 psi  (103  kPa),  a valve  in the  surge  tank cap  opens  and  lets  excess   pressure   escape  to the  atmosphere. ETHYLENE-GLYCOL     MIXTURE   TABLE ETHYLENE-GLYCOL (-6O”F, -51°C) LOWEST   EXPECTED AMBIENT TEMPERATURE “F “C +20 -7 +lO -12 0 -18 -10 -23 -20 -29 -30 -34 -40 40 -50 46 -55 -48 BELOW   -60 BELOW   -51 INHIBITED    (MIL-A-46153) PINTS   PER  GALLON SPECIFIC OF  COOLANT GRAVITY CAPACfTY (68°F)  (20°C) l-112 1.022 2 1.036 2-3J4 1.047 3-l/4 1.055 3-l/2 1.062 4 1.067 4-114 1.073 4-112 4-3J4 USE  ARCTK GRADE   ANTIFREEZE (-9O’F)  (-68%) ARCTfC   GRADE   ANTIFREEZE (-96v)    (-66%) ML-A-1   1755 Freezing   point of -90°F   (-68%). Issued  ready-for-use  and  must not be mixed  with other  liquid. any 2-159