Dodge RAM TRUCK 1500 1995 Service Manual page 301

COOLING SYSTEM SERVICE PROCEDURES 7 - 31
pump pressure to force the valve to open. Coolant
leakage into the pellet container will cause the ther­
mostat to fail in the open position. Thermostats very
rarely stick. Do not attempt to free a thermostat with
a prying device.
The same thermostat is used for winter and sum­
mer seasons. An engine should not be operated with­
out a thermostat, except for servicing or testing.
Operating without a thermostat causes longer engine
warmup time, unreliable warmup performance, in­
creased exhaust emissions and crankcase condensa­
tion that can result in sludge formation.
CAUTION: Do not operate an engine without a ther­
mostat, except for servicing or testing.
THERMOSTAT OPERATION—EXCEPT DIESEL
The thermostat controls the operating temperature
of the engine by controlling the amount of coolant
flow to the radiator. The thermostat is closed below
88°C (192°F). When the coolant reaches this temper­
ature, the thermostat begins to open, allowing cool­
ant flow to the radiator. This provides quick engine
warm-up and overall temperature control. The ther­
mostat is designed to provide a minimum engine op­
erating temperature of 88 to 93°C (192 to 199°F). It
should be fully open for maximum coolant flow dur­
ing operation in hot ambient temperatures of approx­
imately 104°C (220°F). Above 104°C (220°F), coolant
temperature is controlled by the radiator, fan and
ambient temperature.
CAUTION: Never operate the diesel engine without
a thermostat. Without a thermostat, coolant will not
flow to radiator causing engine overheating.
ON-BOARD DIAGNOSTICS
FOR CERTAIN COOLING SYSTEM COMPONENTS
All gasoline powered models are equipped with
On-Board Diagnostics for certain cooling system com­
ponents. Refer to On-Board Diagnostics (OBD) in the
Diagnosis section of this group for additional infor­
mation. If the powertrain control module (PCM) de­
tects low engine coolant temperature, it will record a
Diagnostic Trouble Code (DTC) in the PCM memory.
The DTC number for low coolant temperature is 17.
Do not change a thermostat for lack of heat as indi­
cated 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.
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.
THERMOSTAT REMOVAL—3.9L V-6 OR
5.2/5.9L V-8 GAS POWERED ENGINES
WARNING: DO NOT L O O S E N THE RADIATOR
DRAINCOCK WITH THE S Y S T E M HOT AND P R E S ­
SURIZED. S E R I O U S B U R N S FROM THE COOLANT
CAN OCCUR.
Do not waste reusable coolant. If the solution is
clean, drain the coolant into a clean container for re­
use.
If the thermostat is being replaced, be sure that
the replacement is the specified thermostat for the
vehicle model and engine type.
Factory installed thermostat housings on 3.9L V-6
or 5.2/5.9L V-8 engines are installed on a gasket with
an anti-stick coating. This will aid in gasket removal
and clean-up.
(1) Disconnect negative battery cable at battery.
(2) Drain cooling system until coolant level is be­
low thermostat. Refer to Draining Cooling System in
this group. If not equipped with air conditioning, pro­
ceed to step number 4.
(3) If equipped with air conditioning:
(a) Remove the support bracket (rod) located
near the rear of generator (Fig. 41).
Fig. 41 Support Bracket—Generator Mounting
Bracket-to-lntake Manifold—Typical
(b) The drive belt must be removed. Refer to Belt
Removal/Installation in the Engine Accessory Drive
Belt section of this group.
(c) The generator must be partially removed. Re­
move the two generator mounting bolts. Do not re-