Thermostat-Diesel; Thermostat-Gas Engines; Water Pump - Dodge ram truck 3500 1996 Service Manual

B R COOLING SYSTEM 7 - 31
D I A G N O S I S A N D T E S T I N G ( C o n t i n u e d )
THERMOSTAT—DIESEL
The cooling system used with the diesel engine
provides 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 i f the thermo­
stat is operating properly. This is because coolant
will be held i n the engine until i t 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
vehicle is unloaded. Because of this, lower tempera­
ture 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 elec­
tric 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 i f the outside temperature is below
4°C (40°F). Do not use the Mock heater i f the
outside temperature is above 4°C (40°F).
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. I t attaches to the
front of the vehicle at the grill opening. The cover is
to be used with cool or cold temperatures only.
I f 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.
NOTE: The DRB scan tool cannot be used to mon­
itor engine coolant temperature on the diesel
engine.
(1) To determine i f the thermostat is defective, i t
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. I f contaminants are found, the
thermostat may already be i n 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). I f the valve starts to move before
this temperature is reached, i t is opening too early.
Replace thermostat. The thermostat should be fully
open (valve will stop moving) at 95°C (203°F).
(8) I f the valve is still moving when the water tem­
perature reaches 203°, i t is opening too late. Replace
thermostat.
(9) I f the valve refuses to move at any time,
replace thermostat.
THERMOSTAT—GAS ENGINES
ON-BOARD DIAGNOSTICS
All gasoline powered models are equipped with
On-Board Diagnostics for certain cooling system com­
ponents. Refer to On-Board Diagnostics (OBD) i n the
Diagnosis section of this group for additional infor­
mation. I f the powertrain control module (PCM)
detects low engine coolant temperature, i t will record
a Diagnostic Trouble Code (DTC) in the PCM mem­
ory. The DTC number for low coolant temperature is
17. Do not change a thermostat for lack of heat as
indicated by the instrument panel gauge or by poor
heater performance unless a DTC number 17 is
present. Refer to the Diagnosis section of this group
for other probable causes. For other DTC numbers,
refer to On-Board Diagnostics in the General Diagno­
sis section of Group 14, Fuel Systems.
NOTE: Vehicles equipped with a 5.9L diesel engine
do not have the DTC number 17 check engine lamp
feature.
The DTC can also be accessed through the DRB
scan tool. Refer to the appropriate Powertrain Diag­
nostic Procedures manual for diagnostic information
and operation of the DRB scan tool.
WATER PUMP
A quick test to determine i f pump is working is to
check i f heater warms properly. A defective water
pump will not be able to circulate heated coolant
through the long heater hose to the heater core.