TM 5-3895-383-24 Problem 26:  Above Normal Coolant Temperature Probable Cause(s): Low Coolant Level Incorrect Mixture Air In Cooling System Fan Clutch Temperature Gauge Sending Unit Radiator Radiator Cap Incorrect Fan, Fan Or Shroud Not In Correct Position Loose Belt(s) Hose(s) Air Inlet Restriction Exhaust Restriction Shunt Line Water Temperature Regulator Defective Water Pump Air Flow Through Engine Compartment Aftercooler Outside Temperature Operate At High Altitude Engine Used In Lug Condition Fuel Setting Fuel Injection Timing 1. Low coolant level: If  the  coolant  level  is  too  low,  not  enough  coolant will go through the engine and radiator.  This lack of coolant  will  not  take  enough  heat  from  the  engine and  there  will  not  be  enough  flow  of  coolant  to release the heat into the cooling air.  Low coolant level  is  caused  by  leaks  or  incorrect  fling  of  the radiator.  With the engine cool, be sure that coolant can be seen at the low end of the fill neck on the radiator top tank. 2. Incorrect mixture: Check  the  mixture  of  antifreeze  and  water.    The mixture should be approximately 50 percent water and  50  percent  antifreeze  with  a  3  to  6  percent coolant  conditioner.    If  the  system  is  not  correct drain  the  system  as  needed  and  put  the  correct mixture of water, antifreeze and coolant conditioner in the cooling system. 3. Air in cooling system: Air can enter the cooling system  in  different  ways. The most common causes are not filling the cooling system  correctly,  and  combustion  gas  leaking  into the cooling system.  Combustion gas can get into the    system    through    inside    cracks,    a    defective cylinder  head,  or  head  gasket.    Air  in  the  cooling system   causes   a   reduction   in   coolant   flow   and bubbles  in  the  coolant.    Air  bubbles  hold  coolant away from the engine parts, preventing the transfer of heat to the coolant. 4. Fan clutch: A  fan  clutch  not  turning  a  the  correct  speed  can cause improper air speed across the radiator core. The  lack  of  proper  air  flow  across  the  core  can cause    the    coolant    not    to    cool    to    the    proper temperature differential. 5. Temperature gauge: A temperature gauge which does not work correctly will   not   show   the   correct   temperature.      If   the temperature gauge shows that the coolant temperature   is   too   hot   but   other   conditions   are normal, either install a gauge of known accuracy, or check     the     cooling     system     with     the     8TO470 Thermistor Thermometer Group. 6. Sending unit: In  some  conditions  the  temperature  sensor  in  the engine   sends   signals   to   a   sending   unit   which converts   these   signals   to   an   electrical   impulse which  is  used  by  a  mounted  gauge.    If  for  some reason the sending unit malfunctions or the electric wire  breaks  or  shorts  out  the  gauge  can  show  an incorrect reading. 7. Radiator: Restriction to flow of coolant through core tubes of radiator  of  air  flow  restriction.    Check  for  debris between the fins of the radiator core which prevents free air flow through the radiator core.  Check the radiator for debris, dirt, or deposits on the inside of the   radiator   core   which   will   prevent   tree   flow   of coolant through the radiator. A radiator which is too small does not have enough area to release the heat to the cooling air.  This will cause  the  engine  to  run  at  a  higher  than  normal temperature.        Make    sure    the    radiator    size    is according to the OEMs specifications. 6-48