MOTOR TRUCK SERVICE MANUAL
COOLING SYSTEM
GENERAL
DESCRIPTION
contracts allowing the return spring on the shutter
An internal combustion engine operated at a
assembly to gradually close the shutter blades until the
constant predetermined temperature has less wear and
coolant is again raised to the required temperature.
greater efficiency. To provide this constant temperature,
Because of the modulated control, the shutter blades
shutters are mounted in front of the radiator. The shutter
do not necessarily move from a fully closed to a fully
blades are opened and closed automatically by a
open position or vise-versa. They open only that amount
thermostatic modulated control, Fig. 1.
necessary to maintain a constant operating temperature.
The slight temperature rise possible when an engine is
shutdown will not affect the position of the shutter blades.
The blades should be in the closed position when the
engine temperature is cold.
Failure of the shutter control thermostat will not result
in engine damage because the expansive properties of
the thermostat element will always keep the blades in an
open position.
NOTE: Do not discard thermostat because plunger
is extended.
A small spring is provided to return piston of
thermostat if shutter should be held open while engine
cools. However, should piston be in extended position
Fig. 1 Radiator Shutter Control.
when cold, it is necessary that thermostat be heated to
operating temperature before attempting to return.
The operating temperature of the engine is
Cover radiator completely and bring temperature to
dependent upon the shutter control thermostat setting,
normal, then apply spring tension and piston will return
therefore, it is important that a shutter control of the
when engine cools. If thermostat is removed, heat in
correct degree rating be installed (see "NOTE ", page 6).
circulating water and apply spring tension until it cools.
OPERATION
NEVER FORCE piston back when cold, as serious
The modulated shutter control is mounted in the
damage will result. Should the piston not return to
radiator bottom tank with the thermostat unit extending
proper height, the neoprene diaphragm may be ruptured
into the coolant. When the engine is cold, the engine
and thermostat will have to be replaced.
thermostat and radiator shutter blades are closed. The
REMOVAL
shutter blades are held closed by a spring in the shutter
Shutter Control Assembly
assembly. When the temperature of the coolant reaches
To remove modulated shutter control, drain coolant
the opening temperature of the engine thermostat, the
from radiator. Disconnect control rod from control lever.
thermostat opens allowing the coolant to circulate
Remove the two (2) bolts securing shutter control to
through the radiator. The shutter control thermostat
bottom tank of radiator and take out control assembly.
element senses the increase in coolant temperature and
Shutter Assembly
expands, moving the control lever which is connected to
To remove shutter assembly, take out bolts securing
the shutters by means of a rod. This action gradually
frame assembly and lift out shutter assembly.
opens the shutter blades until the coolant temperature
rise is halted at the required setting.
If atmospheric temperatures should cause the
coolant temperature to receed, the shutter control
thermostat element
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