TM 5-3895-383-24 8. Radiator cap: A   pressure   drop   in   the   radiator   can   cause   the boiling point to lower causing the cooling system to boil over.  A cooling system pressure tester may be used to check the cooling system pressure as well as the pressure cap relief valve.  If the cap fails the test,  check  the  rubber  seal  on  the  cap  as  well  as the operation of the pressure relief valve. 9. Incorrect fan, fan or shroud not in correct position: An  incorrect  fan,  or  a  fan  or  shroud  in  a  wrong position will cause a reduction or a loss of air flow through the radiator.  The fan must be large enough to send air through most of the area of the radiator core. 10. Loose belt(s): Loose    fan    or    water    pump    belts    will    cause   a reduction in air and coolant flow.  Tighten the belts according to the Belt Tension Charts. 11. Hose(s): Defective hoses with  leaks  can  normally  be  seen. Hoses that have no visual leaks can collapse (pull together) during operation and cause a restriction in the flow of coolant.  Hoses become soft and/or get cracks after a period of time.  The inside of a hose can deteriorate, and the loose particles of the hose can cause a restriction of the coolant flow. 12. Air inlet restriction: Restriction  of  the  air  coming  into  the  engine  can cause  high  cylinder  temperatures  and  more  than normal   amount   of   heat   to   pass   to   the   cooling system.        Check    for    restriction    with    a    water manometer or a vacuum gauge (which measures in inches of water).  Connect the gauge to the engine air inlet between the air cleaner and the inlet to the turbocharger.      With   the   gauge   installed,   run   the engine  at  full  load  rpm  and  check  the  restriction. Maximum restriction of the air inlet is 635 mm (25 in)    of    water.        If    the    indication    is    higher    than maximum permissible restriction, remove the foreign material from the filter element, or install a new   filter   element   and   check   for   the   restriction again.  If the indication is still too high, there must be a restriction in the inlet piping. 13. Exhaust restriction: Restriction   in   the   exhaust   system   can   cause   high cylinder temperatures and more than normal amount of heat to pass to the cooling system.  To check if there is an exhaust restriction, make a visual inspection of the exhaust system.  Check for damage to piping or for a defective  muffler.    If  no  damage  is  found,  check  the exhaust  system  for  back  pressure  from  the  exhaust (pressure  difference  measurement  between  exhaust outlet and atmosphere).  The back pressure must not be more than 1016 mm (40 in) of water.  Check the system   by   removing   the   exhaust   pipes   from   the exhaust manifolds.  With the exhaust pipes removed, start  and  run  the  engine  to  see  if  the  problem  is corrected. 14. Shunt line: A restriction of the shunt line from the radiator top tank to the engine water pump inlet, or a shunt line not   installed   correctly,   will   cause   a   reduction   in water   pump   efficiency.      The   result   will   be   low coolant flow and overheating. 15. Water temperature regulator: A water temperature regulator that does not open, or  only  opens  part  of  the  way,  can  cause  above normal   heating.      To   test   the   water   temperature regulator, see the Testing and Adjusting Section of the Service Manual. 16. Defective water pump: A  water  pump  with  a  loose  or  damaged  impeller does  not  pump  enough  coolant  for  correct  engine cooling.    Remove  the  water  pump  and  check  for damage  to  the  impeller.    If  the  impeller  has  no damage,    check    the    impeller    clearance.        The clearance between the impeller and the housing is 0.75 0.25 mm (0.030 to 0.010 in). 17. Air flow through engine compartment: The  air  flow  through  the  radar  comes  out  of  the engine   compartment.      Make   sure   the   filters,   air conditioners and similar items are not installed in a way which prevents free flow of air into and out of the engine compartment. 18. Aftercooler: Restriction    of    air    flow    through    the    air    to    air aftercooler   (if   equipped).      Check   for   debris   or deposits  which  would  prevent  the  free  flow  of  air through the aftercooler. 19. High outside temperature: When  outside  temperatures  are  too  high  for  the rating  of  the  cooling  system,  there  is  not  enough temperature difference between the outside air and coolant temperatures. 6-49