SERVICE MANUAL WATER PUMP, THERMOSTAT & IDLER PULLEYS Section 9 e. IMPORTANT:  Impeller to housing clearance 4 and 8 vane pumps: 0.25 - 1.17 mm (0.010 - 0.046 in.) 7. Vane Pumps: 0.31 - 1.63 mm (0.012 - 0.064 in) Determine impeller to housing clearance as follows: 1. With  feeler  gauges  in  place  press  impeller until feeler gauges (2, Fig. 25) are snug. 2. Use  a  sleeve  (1,  Fig.  25)  under  press  ram as shaft will protrude slightly from impeller. NOTE:  Use an appropriate size feeler gauge (0.97 mm [0.038 in.] ) for the 7 vane pump. 19. Using a new gasket, secure water pump to crankcase front cover. 20. Install water pump pulley, fan and spacer, if one was used. THERMOSTAT The thermostat is used to control the temperature of the engine coolant.  It is located in a housing attached to the cylinder  head.    The  housing  is  arranged  to  return  the coolant to the radiator or to by-pass it depending on the coolant temperature. When   the   coolant   is   more   than   82°C   (180F),   the thermostat   is   actuated,   becoming   fully   open   at   94° (202F).  During this time, the coolant is directed by the thermostat, in the thermostat housing, to flow to the top water tank of the radiator for air cooling.  Coolant in the engine is replaced with coolant from the radiator bottom tank to the water pump. REMOVAL Remove the Thermostat as follows: 1. Disconnect the hose. 2. Remove    the    bolts    and    lock    washers,    then remove the thermostat housing. 3. Remove   the   thermostat   housing   gasket   and discard. CLEANING, INSPECTION AND REPAIR CLEANING Clean the Thermostat Housing as follows: 1. Wash the housing in solvent. 2. Dry with compressed air. INSPECTION AND REPAIR Inspect and Repair the Thermostat as follows: 1. Inspect for accuracy as follows: a. Suspend the thermostat in a container of water.  DO NOT allow the thermostat to touch the sides or bottom of the container. b. Heat the container. c. Measure the water temperature with a thermometer suspended in container. d. If the thermostat opening temperature is 6C (10F) above or below the 82C to 94°C (180F to 202F) rating, replace the thermometer. 2. Visually inspect the housing for cracks and burrs.  Replace if necessary. 3. Inspect the housing seal for brittleness, cracks or wear.  Replace if necessary. CGES-185-3 PRINTED IN UNITED STATES OF AMERICA Page 16