TM   10-3930-643-20 ENGINE,  FUEL,  EXHAUST  AND  COOLING  TROUBLESHOOTING  AND  MAINTENANCE.  (cont) 4-6. Cooling   System   Troubleshooting. MALFUNCTION TEST OR INSPECTION CORRECTIVE   ACTION b . OVERHEATING.  (cont) Step   4. Check   coolant   circulation.   (cont) WARNING Remove   radiator   cap   slowly   to   relieve   pressure   before   completely removing   it   when   the   engine   is   hot. Failure   to   follow   this   procedure could   cause   SEVERE   INJURY. If   you   are   scalded   by   steam,   seek   medical aid    immediately. (b)   Check   for   loss   of   pressure.   Check   radiator   cap,   Refer   to   paragraph 4-27. If   radiator   cap   is   loose,   tighten   it. If   radiator   cap   is   defective,   replace   cap.   Refer   to   paragraph   4-27. If   cap   is   correctly   installed,   go   on   to   (c). (c)   Start   engine   and   check   water   pump   operation.   Remove   radiator   cap and   check   for   restriction   by   observing   coolant   circulation. Drain   if   restrictions   are   found. Refer   to   paragraph   4-27. Disconnect   hoses   and   reverse   flush   the   radiator   and   crankcase. (d)   Inspect   and   test   thermostat.   Refer   to   paragraph   4-29. Replace   thermostat,   if   necessary. c.  ENGINE  RUNS  COLD. Step   1. Operation   in   extremely   cold   weather   may   cause   this   problem. Cover   radiator. If   problem   continues,   go   to   step   2. 4-20