TM 10-3930-671-24 system ineffective to properly maintain normal operating temperatures.  The appearance of rust in the radiator or coolant is a warning that the corrosive inhibitor has host its  effectiveness  and  should  be  cleaned  before  adding fresh coolant. Dependable     cleaning     compounds     should     be     used. Follow   the   procedure   recommended   by   the   supplier. This  is  of  prime  importance  because  different  cleaners vary  in  concentration  and  chemical  compositions.    After cleaning and flushing, the system should be filled with an approved  anti-freeze   compound   containing   a   rust   and corrosion inhibitor. REVERSE FLOW FLUSHING Whenever   a   cooling   system   is   badly   rustclogged   as indicated  by  overflow  loss  or  abnormally  high  operating temperatures,     corrective cleaning by reverse flow flushing  will  most  effectively  remove  the  heavy  deposits of   sludge,   rust   and   scale.      The   reverse   flow   flushing should    be    performed    immediately    after    draining    the cleaning solution.  It is advisable to flush the radiator first, allowing the engine to cool as much as possible. Reverse flush the radiator, as follows: 1. Discontent the hoses at the engine. 2. Put radiator cap on tight. 3. Clamp the flushing gun in the lower hose with a hose clamp. 4. Turn on the water and let it fill the radiator. 5. Apply   air   pressure   gradually,   to   avoid   radiator damage. 6. Shut off the air, again fill the  radiator  with  water and apply air pressure.  Repeat until the flushing stream runs out clear. 7. Clean and inspect radiator cap. To reverse, flush the engine water jacket: 1. Remove the thermostat. 2. Clamp the flushing gun in the upper hose. 3. Partly  close  the  water  pump  opening  to  fill  the engine jacket with water before applying the air. 4. Follow  the  same  procedure  outlined  above  for the radiator by alternately filling the water jacket with water and blowing it out with air 5.5 Bar (80 PSI) until the flushing stream is clear. TESTING THERMOSTAT Remove  the  water  outlet  elbow.    Before  testing,  clean and examine the thermostat.  If  the  valve  can  be  pulled or pushed off its seat with only  a  slight  effort  when  cold or  it  does  not  seat  properly,  the  unit  is  defective  and should be replaced. Thermostat  operation  can  be  checked  In  the  following method: 1. Hang  thermostat  by  its  frame  in  a  container  of water so that it does not touch the bottom. 2. Heat   the   water   slowly   and   check   temperature with a thermometer. 3. If the valve does not start to open at temperatures   of   180   -   200"F   81-   930C   or   it opens   well   before   the   180°F   (81   C)   point   Is reached, the thermostat should be replaced. F-147