Operation and maintenance manual

QSB4.5 and QSB6.7 Coolant Thermostat
Section A - Adjustment, Repair, and Replacement Page A-11
Inspect the thermostat for external damage. Also inspect
for cracks, embedded debris, missing check balls,
damaged seat, and other damage.
Replace the thermostat if any damage is found.
Measure
If the thermostat is suspected to be malfunctioning, the
opening temperature of the thermostat should be
measured to determine if the thermostat is functioning
properly.
NOTE: Do not allow the thermostat or thermometer to
touch the container.
Suspend the thermostat and a 100°C [212°F]
thermometer in a container of water.
Heat the water and check the thermostat as follows:
NOTE: There are two different temperature range
thermostats available, depending on the application. The
nominal operating temperature is stamped on the
thermostat. To verify the correct temperature range
thermostat is installed, make sure to reference the
appropriate part information resources.
The thermostat must meet the following criteria:
82°C [180°F] Nominal Temperature Thermostat
Thermostat Opening Temperature
°C °F
Initial Opening 79 MIN 175
83 MAX 182
Fully Opened 94 MAX 202
88°C [190°F] Nominal Temperature Thermostat
Thermostat Opening Temperature
°C °F
Initial Opening 86 MIN 186
89 MAX 193
Fully Opened 97 MAX 207