flow to the radiator. When coolant temperature is below
83° C (181° F), the thermostat is closed (Fig. 50).
When coolant temperature reaches 83° C (181°
F) the thermostat begins to open allowing coolant flow to the radiator.
This provides quick engine wam-up and overall temperature control. The
thermostat is designed to provide a minimum engine operating temperature
of 83° C (181° F) and to be fully open for maximum coolant flow
at approximately 95° C (203°F). Above 95°C (203°F), coolant
temperature is controlled by the radiator, fan and ambient temperature.
The air bleeds (jiggle pins) that were used on
the thermostats of diesel engines in previous years are no longer used.
They have been replaced by a vertically mounted one-way check valve (jiggle
pin) and a rubber bypass hose. The check valve is used as as a servicing
feature and will vent air when the system is being filled. It is also
used to block the flow of coolant during engine operation (all coolant
will pass through the thermostat).
Water pressure (or flow) will Hold the pin closed.
When the engine is off, the check valve will be in
the open position. When the engine is operating the check valve will be
in the closed position.
The, check valve is located inside of a brass
fitting. This fitting is threaded into the front of the cylinder head
(Fig. 51). It is connected to the thermostat housing with a rubber hose
and screw-type clamps (ft. 51).
THERMOSTAT REMOVAL - DIESEL ENGINE
WARNING: DO NOT LOOSEN THE RADIATOR CAP OR DRAIN COCK
WITH THE SYSTEM HOT AND PRESSURIZED. SERIOUS BURNS FROM THE COOLANT COULD
Do not waste reusable coolant.
If the solution is clean, drain the coolant into a clean container for
(1) Disconnect both negative battery cables from
accessory drive belt. Refer to Belt Removal/Installation in the Engine
Accessory Drive Belt section in this group. (3)
Drain cooling system until coolant level is below thermostat. Refer to
Draining Cooling System in this section.
WARNING: CONSTANT TENSION HOSE CLAMPS ARE USED ON MOST
COOLING SYSTEM HOSES. WHEN REMOVING OR INSTALLING, USE ONLY TOOLS DESIGNED
FOR SERVICING THIS TYPE OF CLAMP, SUCH AS SPECIAL TOOL NUMBER 6094 (FIG.
43). SNAP-ON CLAMP TOOL NUMBER HPC-20 MAY BE USED FOR LARGER CLAMPS. ALWAYS
WEAR SAFETY GLASSES WHEN SERVICING CONSTANT TENSION CLAMPS.
CAUTION: A number or letter is stamped into the tongue
of constant tension clamps. If replacement is necessary, use only an original
equipment clamp with a matching number or letter.
(4) Remove radiator base clamp
and hose from thermostat housing. A special clamp tool (Fig. 43) must
be used to remove the constant tension clamps.
(5) Remove the hose clamp and check valve hose
at thermostat housing (Fig. 52).
(6) Remove the two upper generator bracket mounting
bolts (Fig. 53).
(7) Remove the upper generator mounting bracket
(8) Loosen but do not remove the generator lower