ARMY TM 9-6115-670-14&P 4-54 4.22.  THERMOSTAT. This task covers: a. Test b. Replace INITIAL SETUP Tools Thermometer, Glass (Item 21, Appendix B) Small Pan Equipment Condition Engine stopped and allowed to cool completely. MASTER ON-OFF switch on APU controller set to OFF. Materials/Parts Thermostat Sealing Compound 88-20595-2 (Item 18, Appendix F) Gasket, Thermostat Housing (Item 10, Appendix J) TEST a.  Remove thermostat (perform steps a through c of REPLACE procedure). b.  Suspend thermostat (4, Figure 4-9) by a string with one end of string inserted between the valve and seat.   c.  Immerse the thermostat (4) in a pan of water (5). d.  Heat the water gradually and read the temperature on the thermometer (3) when the valve opens making the thermostat fall off the string.  The valve should open between 157.1°F and 162.5°F (69.5°C and 72.5°C). e.  If the valve does not open properly, replace the thermostat (4). REPLACE a.  Loosen two clamps (1) and remove radiator water hose (2) from thermostat housing (7). b.  Remove two bolts and lock washers (9), thermostat housing (8) and gasket (7). c.  Remove thermostat (4) from temperature sensor block (6). d.  Thoroughly clean temperature sensor block (6) and thermostat housing (8). WARNING Hot  coolant  is  under  pressure.    Do  not  remove radiator cap when engine is hot.  Allow engine to cool   completely   before   removing   radiator   cap.   Once cooling has occurred, loosen cap slightly to relieve any excess pressure before removing the cap  completely.    Failure  to  observe  this  warning could result in burns or `injury to personnel. NOTE Valve should completely open to 0.2367 in. (6 mm) at 185°F (85°C).