Chrysler RAM TRUCK 2500 1994 Service Manual page 288

• COOLING SYSTEM 7 - 33
flow to the radiator. When coolant temperature is be­
low 83°C (181°F), the thermostat is closed (Fig. 50).
Fig. 50 Thermostat Operation—5.9L Diesel—Typical
When coolant temperature reaches 83°C (181°F),
the thermostat begins to open allowing coolant flow
to the radiator. This provides quick engine warm-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 tempera­
ture.
The air bleeds (jiggle pins) that were used on the
thermostats of diesel engines i n previous years are
no longer used. They have been replaced by a verti­
cally mounted one-way check valve (jiggle pin) and a
rubber bypass hose. The check valve is used as a ser­
vicing feature and will vent air when the system is
being filled. I t is also used to block the flow of cool­
ant 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 i n
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). I t is connected to the thermostat
housing with a rubber hose and screw-type clamps
(Fig. 51).
THERMOSTAT REMOVAL—DIESEL E N G I N E
WARNING: DO NOT L O O S E N T H E RADIATOR
DRAINCOCK WITH T H E S Y S T E M HOT AND P R E S ­
SURIZED. S E R I O U S BURNS FROM T H E C O O L A N T
CAN O C C U R .
Fig. 51 One-Way Check Valve (Jiggle Pin) Location
Do not waste reusable coolant. I f the solution is
clean, drain the coolant into a clean container for re­
use.
(1) Disconnect both negative battery cables from
both batteries.
(2) Remove accessory drive belt. Refer to Belt Re­
moval/Installation i n the Engine Accessory Drive Belt
section i n this group.
(3) Drain cooling system until coolant level is be­
low thermostat. Refer to Draining Cooling System i n
this section.
WARNING: CONSTANT TENSION H O S E C L A M P S
A R E U S E D ON MOST COOLING S Y S T E M H O S E S .
WHEN REMOVING OR INSTALLING, U S E ONLY
T O O L S D E S I G N E D F O R SERVICING THIS T Y P E O F
CLAMP, S U C H A S S P E C I A L CLAMP T O O L (NUMBER
8094) (FIG. 43). SNAP-ON CLAMP T O O L (NUMBER
HPC-20) MAY B E U S E D F O R L A R G E R C L A M P S . A L ­
WAYS W E A R S A F E T Y G L A S S E S WHEN SERVICING
CONSTANT TENSION C L A M P S .
CAUTION: A number or letter is stamped into the
tongue of constant tension clamps (Fig. 44). If re­
placement is necessary, u s e only an original equip­
ment clamp with a matching number or letter.
(4) Remove radiator hose 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).