Dodge RAM TRUCK 1500 1995 Service Manual page 305

B R
Fig. 50 One-Way Check Vaive (Jiggle Pin) Location
THERMOSTAT DIAGNOSIS—DIESEL ENGINE
The cooling system used with the diesel engine pro­
vides the extra coolant capacity and extra cooling
protection needed for higher GVWR (Gross Vehicle
Weight Rating) and GCWR (Gross Combined Weight
Rating) vehicles.
This system capacity will not effect warm up or
cold weather operating characteristics if the thermo-
COOLING SYSTEM SERVICE PROCEDURES 7 - 35
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 in 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 They have been replaced by a verti­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. It 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 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. 50). It is connected to the thermostat
housing with a rubber hose and screw-type clamps
(Fig. 50).
stat is operating properly. This is because coolant
will be held in the engine until it reaches the ther­
mostat "set" temperature.
Diesel engines, due to their inherent efficiency are
slower to warm up than gasoline powered engines,
and will operate at lower temperatures when the ve­
hicle is unloaded. Because of this, lower temperature
gauge readings for diesel versus gasoline engines
may, at times be normal.
Typically, complaints of low engine coolant temper­
ature are observed as low heater output when com­
bined with cool or cold outside temperatures.
To help promote faster engine warm-up, the electric
engine block heater must be used with cool or cold
outside temperatures. This will help keep the engine
coolant warm when the vehicle is parked. Use the
block heater if the outside temperature is below 4°C
(40°F). Do not use the block heater if the out­
side temperature is above 4°C (40°F)
o
A "Cold Weather Cover" is available from the parts
department through the Mopar Accessories product
line. This accessory cover is designed to block airflow
entering the radiator and engine compartment to
promote faster engine warm-up. It attaches to the
front of the vehicle at the grill opening. The cover is
to be used with cool or cold temperatures only.
If used with high outside temperatures, serious
engine damage could result. Refer to the litera­
ture supplied with the cover for additional informa­
tion.
TESTING:
The following test procedure is to be used for the
diesel engine only.
The DRB scan tool cannot be used to monitor
engine coolant temperature on the diesel en­
gine.
(1) To determine if the thermostat is defective, it
must be removed from the vehicle. Refer to Thermo­
stats for removal and installation procedures.
(2) After the thermostat has been removed, exam­
ine the thermostat and inside of thermostat housing
for contaminants. If contaminants are found, the
thermostat may already be in a "stuck open" position.
Flush the cooling system before replacing thermostat.
Refer to Cooling System Cleaning/Reverse Flushing
in this group for additional information.
(3) Place the thermostat into a container filled
with water.
(4) Place the container on a hot plate or other suit­
able heating device.
(5) Place a commercially available radiator ther­
mometer into the water.
(6) Apply heat to the water while observing the
thermostat and thermometer.
(7) When the water temperature reaches 83°C
(181°F) the thermostat should start to open (valve
will start to move). If the valve starts to move before