TM 5-6115-593-34 NAVFAC P-8-631-34 TO-35C2-3-463-2 oil  heat  exchangers  are  also  utilized.    A  liquid  coolant under  pressure  enters  the  water  jackets  absorbing  heat from   the   cylinders   and   other   components   described above, and by the time it reaches the outlet has risen in temperature.      Water   cooling   systems   are   configured such that the temperature differential between inlet and outlet does not exceed 10 to 12F  (-12  to  -11°C).    It  is not good practice, and may be destructive to the engine to have a low intake temperature. 17-40.    The  coolant  leaving  the  engine  outlet  enters  a radiator   heat   exchanger   to   exchange   its   heat   to   the environment. 17-41.  RADIATOR COOLING.  See table 17-4. a. Provide   an   entrance   for   fresh   air   at   least   as large   in   area   as   the   radiator   itself.      Do   not depend  solely  on  apertures  such  as  windows, etc.    Where  possible,  inlet  shutters  are  utilized to increase the inlet opening area by a factor of one quarter to one half that of the radiator area. In areas of extremely cold ambient temperatures,   thermostatically   controlled   inlet shutters should be considered. b. Cool  inlet  air  should  not  be  required  to  find  its way    to    the    engine    room    through    stairwells, corridors, etc., nor should it be required to travel upward through a duct. Table 17-4.  Radiator and Crankcase Capacities Radiator and ................................................ 54 gallons block capacities (204 liters) Crankcase oil ............................................... 18 gallons capacity (168 liters) 17-42.    A  radiator  is  a  closed  system  heat  exchanger consisting   of   finned   tubes   through   which   the   engine coolant  passes.    The  heat  exchanging  air  stream  over the fins is produced by a beltdriven, pusher-type fan (air flow from rear of set towards the radiator).  Cooling air is drawn over the engine and pushed through the radiator into a duct leading to the outlet vent, or unducted toward the  outlet  vent.      A  radiator  cannot  itself  absorb  heat (except   for   the   very   small   amount   to   warm   its   own metal)  and  is  not  to  be  regarded  as  a  bottomless  pit capable   of   absorbing   unlimited   heat.      The   radiator exposes the finned surface of its tubes to the passing air stream to carry off engine heat. 17-43.  A free supply of fresh air must be available and recirculation  of  the  air  must  be  avoided.    If  the  cooling air is allowed to recirculate it would soon acquire enough heat to raise the ambient temperature to approximately the   same   temperature   as   the   radiator,   resulting   in engine   overheating.      A   few   basic   rules   should   be observed in locating a radiator cooled generating unit. c. Provide    an    exit    for    heated    air,    preferably ducted,   allowing   it   to   be   carried   completely away.    The  exit  opening  should  be  larger  than the     inlet     opening     to     compensate     for     the expansion   of   air   due   to   heat.      Bends   in   the exhaust duct should be avoided where possible, but    if    they    are    required,    they    should    be proportionally enlarged. d. Cooling   fan   pressure   generally   should   not   be required to force air through semiclosed openings, louvers, swinging traps, etc. However, if gravity drop louvers are utilized, the louvers should be lightweight metal. e. Where possible, position so that the direction of fan output is directly toward the outlet. f. Avoid ducting so the outlet constructed to the air must make one or more right angle bends after leaving. g. Where   possible,   position   the   engine   so   that minimum distance 17-12