Operation and maintenance manual

Coolant Thermostat QSB4.5 and QSB6.7
Page A-10 Section A - Adjustment, Repair, and Replacement
CAUTION
Never operate the engine without a thermostat.
Without a thermostat, the path of least resistance for
the coolant is through the bypass to the water pump
inlet. This can cause the engine to overheat.
CAUTION
A missing check ball can cause the engine to run
cold, resulting in engine damage.
The thermostat contains two check balls to vent air past
the thermostat when it is closed. This helps to vent air
during the cooling system fill process.
NOTE: Some off-highway applications use a thermostat
with one check ball. When replacing a thermostat, always
be sure to use the same part number. Though an
incorrect thermostat will physically fit, it will lead to
improper engine operation.
Remove
Remove the water outlet connection capscrews.
Remove the water outlet connection.
Remove the thermostat.
Clean and Inspect for Reuse
CAUTION
Do not let any debris fall into the thermostat cavity
when cleaning the gasket surfaces. Damage to the
cooling system and engine can occur.
Clean the mating surfaces with an abrasive pad, Part
Number 3823258 or equivalent, and a clean cloth.