Dodge Dakota (R1). Manual — part 256
(2) Insert block heater assembly with element loop
pointing at twelve o’clock (Fig. 7).
(3) With block heater fully seated, tighten center
screw to 2 N·m (17 in. lbs.) torque.
(4) Refill cooling system (Refer to 7 - COOLING -
STANDARD PROCEDURE).
(5) Start and warm the engine. Check for leaks.
ENGINE COOLANT
TEMPERATURE SENSOR
DESCRIPTION
The Engine Coolant Temperature (ECT) sensor is
used to sense engine coolant temperature. The sensor
protrudes into an engine water jacket.
The ECT sensor is a two-wire Negative Thermal
Coefficient (NTC) sensor. Meaning, as engine coolant
temperature increases, resistance (voltage) in the
sensor decreases. As temperature decreases, resis-
tance (voltage) in the sensor increases.
OPERATION
At key-on, the Powertrain Control Module (PCM)
sends out a regulated 5 volt signal to the ECT sensor.
The PCM then monitors the signal as it passes
through the ECT sensor to the sensor ground (sensor
return).
When the engine is cold, the PCM will operate in
Open Loop cycle. It will demand slightly richer air-
fuel mixtures and higher idle speeds. This is done
until normal operating temperatures are reached.
The PCM uses inputs from the ECT sensor for the
following calculations:
• for engine coolant temperature gauge operation
through CCD or PCI (J1850) communications
• Injector pulse-width
• Spark-advance curves
• ASD relay shut-down times
• Idle Air Control (IAC) motor key-on steps
• Pulse-width prime-shot during cranking
• O2 sensor closed loop times
• Purge solenoid on/off times
• EGR solenoid on/off times (if equipped)
• Leak Detection Pump operation (if equipped)
• Radiator fan relay on/off times (if equipped)
• Target idle speed
REMOVAL - 3.9L/5.2L/5.9L
The engine coolant temperature sensor is installed
into a water jacket at front of intake manifold near
rear of generator (Fig. 8).
WARNING: HOT, PRESSURIZED COOLANT CAN
CAUSE INJURY BY SCALDING. COOLING SYSTEM
MUST BE PARTIALLY DRAINED BEFORE REMOV-
ING THE COOLANT TEMPERATURE SENSOR.
(1) Partially drain cooling system (Refer to 7 -
COOLING - STANDARD PROCEDURE).
(2) Disconnect electrical connector from sensor
(Fig. 8).
(3) Engines
with
air
conditioning:
When
removing the connector from sensor, do not pull
directly on wiring harness. Fabricate an L-shaped
hook tool from a coat hanger (approximately eight
inches long). Place the hook part of tool under the
connector for removal. The connector is snapped onto
the sensor. It is not equipped with a lock type tab.
(4) Remove sensor from intake manifold.
REMOVAL - 4.7L
WARNING: HOT, PRESSURIZED COOLANT CAN
CAUSE INJURY BY SCALDING. COOLING SYSTEM
MUST BE PARTIALLY DRAINED BEFORE REMOV-
ING THE ENGINE COOLANT TEMPERATURE (ECT)
SENSOR.
The ECT sensor is located near the front of the
intake manifold (Fig. 9).
(1) Partially drain cooling system (Refer to 7 -
COOLING - STANDARD PROCEDURE).
(2) Disconnect electrical connector from ECT sen-
sor.
(3) Remove sensor from intake manifold.
Fig. 8 Engine Coolant Temperature Sensor—5.2L/
5.9L Engines—Typical
1 - GENERATOR
2 - A/C COMPRESSOR
3 - ENGINE COOLANT TEMPERATURE SENSOR
4 - ELEC. CONN.
7 - 36
ENGINE
AN
ENGINE BLOCK HEATER - 4.7L (Continued)
REMOVAL - 2.5L
WARNING: HOT, PRESSURIZED COOLANT CAN
CAUSE INJURY BY SCALDING. COOLING SYSTEM
MUST BE PARTIALLY DRAINED BEFORE REMOV-
ING THE COOLANT TEMPERATURE SENSOR.
(1) Partially drain cooling system (Refer to 7 -
COOLING - STANDARD PROCEDURE).
(2) Disconnect electrical connector from sensor
(Fig. 10).
(3) Remove sensor from thermostat housing.
INSTALLATION - 3.9L/5.2L/5.9L
The engine coolant temperature sensor is installed
into a water jacket at front of intake manifold near
rear of generator (Fig. 8).
(1) Install sensor.
(2) Tighten to 11 N·m (8 ft. lbs.) torque.
(3) Use long needlenose pliers to connect electrical
connector to sensor. The sensor connector is symmet-
rical (not indexed). It can be installed to the sensor
in either direction.
(4) Replace any lost engine coolant (Refer to 7 -
COOLING - STANDARD PROCEDURE).
INSTALLATION - 4.7L
(1) Install sensor.
(2) Tighten to 11 N·m (8 ft. lbs.) torque.
(3) Connect electrical connector to sensor.
(4) Replace any lost engine coolant (Refer to 7 -
COOLING - STANDARD PROCEDURE).
INSTALLATION - 2.5L
(1) Install sensor.
(2) Tighten to 11 N·m (8 ft. lbs.) torque.
(3) Replace any lost engine coolant (Refer to 7 -
COOLING - STANDARD PROCEDURE).
ENGINE COOLANT
THERMOSTAT - 2.5L
DESCRIPTION
CAUTION: Do not operate an engine without a ther-
mostat, except for servicing or testing.
The thermostat (Fig. 11) on all gas powered
engines is located beneath the thermostat housing at
the front of the intake manifold.
The thermostat is a wax pellet driven, reverse pop-
pet choke type.
Fig. 9 Engine Coolant Temperature Sensor—4.7L
V–8 Engine
1 - ECT SENSOR
2 - MOUNTING BOLTS (2)
3 - MAP SENSOR
4 - INTAKE MANIFOLD
Fig. 10 Engine Coolant Temperature Sensor—2.5L
Engines
1 - THERMOSTAT HOUSING
2 - ENGINE COOLANT TEMPERATURE SENSOR
3 - ELECTRICAL CONNECTOR
AN
ENGINE
7 - 37
ENGINE COOLANT TEMPERATURE SENSOR (Continued)
Coolant leakage into the pellet container will cause
the thermostat to fail in the open position. Thermo-
stats very rarely stick. Do not attempt to free a ther-
mostat 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,
increased exhaust emissions and crankcase condensa-
tion that can result in sludge formation.
OPERATION
The wax pellet is located in a sealed container at
the spring end of the thermostat. When heated, the
pellet expands, overcoming closing spring tension
and water pump pressure to force the valve to open.
DIAGNOSIS AND TESTING—THERMOSTAT
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) in the
Diagnosis section of this group for additional infor-
mation. If the powertrain control module (PCM)
detects low engine coolant temperature, it will record
a Diagnostic Trouble Code (DTC) in the PCM mem-
ory. Do not change a thermostat for lack of heat as
indicated by the instrument panel gauge or by poor
heater performance unless a DTC is present. Refer to
the Diagnosis section of this group for other probable
causes. For other DTC numbers, (Refer to 25 - EMIS-
SIONS CONTROL - DESCRIPTION).
The DTC can also be accessed through the DRB
scan tool. Refer to the appropriate Powertrain Diag-
nostic Procedures information for diagnostic informa-
tion and operation of the DRB scan tool.
REMOVAL
WARNING:
DO
NOT
LOOSEN
THE
RADIATOR
DRAINCOCK WITH THE SYSTEM HOT AND PRES-
SURIZED. SERIOUS BURNS FROM THE COOLANT
CAN OCCUR.
DO NOT WASTE reusable coolant. If the solution is
clean, drain the coolant into a clean container for reuse.
(1) Disconnect battery negative cable.
(2) Drain the coolant from the radiator until the
level is below the thermostat housing (Refer to 7 -
COOLING - STANDARD PROCEDURE).
(3) Remove radiator upper hose and heater hose at
thermostat housing.
(4) Disconnect wiring connector at engine coolant
temperature sensor.
(5) Remove thermostat housing mounting bolts,
thermostat housing, gasket and thermostat (Fig. 12).
Discard old gasket.
(6) Clean the gasket mating surfaces.
INSTALLATION
(1) Install the replacement thermostat so that the
pellet, which is encircled by a coil spring, faces the
engine. All thermostats are marked on the outer
flange to indicate the proper installed position.
(a) Observe the recess groove in the engine cyl-
inder head (Fig. 13).
(b) Position thermostat into this groove with
arrow and air bleed hole on outer flange pointing up.
(2) Install replacement gasket and thermostat
housing.
CAUTION:
Tightening
the
thermostat
housing
unevenly or with the thermostat out of its recess
may result in a cracked housing.
(3) Tighten the housing bolts to 20 N·m (15 ft. lbs.)
torque.
(4) Install hoses to thermostat housing.
(5) Install electrical connector to coolant tempera-
ture sensor.
(6) Connect battery negative cable.
Fig. 11 Thermostat—Typical
1 - LONG BOLT
2 - GASKET
3 - THERMOSTAT
4 - THERMOSTAT HOUSING
5 - SHORT BOLT
7 - 38
ENGINE
AN
ENGINE COOLANT THERMOSTAT - 2.5L (Continued)
(7) Be sure that the radiator draincock is tightly
closed. Fill the cooling system to the correct level
with the required coolant mixture (Refer to 7 -
COOLING - STANDARD PROCEDURE).
(8) Start and warm the engine. Check for leaks.
ENGINE COOLANT
THERMOSTAT - 3.9L/5.9L
DESCRIPTION
CAUTION: Do not operate an engine without a ther-
mostat, except for servicing or testing.
The thermostat on the 3.9L and 5.9L gas powered
engines is located beneath the thermostat housing at
the front of the intake manifold (Fig. 14).
The thermostat is a wax pellet driven, reverse pop-
pet choke type.
Coolant leakage into the pellet container will cause
the thermostat to fail in the open position. Thermo-
stats very rarely stick. Do not attempt to free a ther-
mostat 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,
increased exhaust emissions and crankcase condensa-
tion that can result in sludge formation.
Fig. 12 2.5LThermostat Removal/Installation
1 - LONG BOLT
2 - GASKET
3 - THERMOSTAT
4 - THERMOSTAT HOUSING
5 - SHORT BOLT
Fig. 13 Thermostat Recess
1 - GROOVE
Fig. 14 Thermostat—5.2L and 5.9L Gas Powered
Engines
1 - THERMOSTAT HOUSING
2 - GASKET
3 - INTAKE MANIFOLD
4 - THERMOSTAT
5 - MACHINED GROOVE
AN
ENGINE
7 - 39
ENGINE COOLANT THERMOSTAT - 2.5L (Continued)
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