air JEEP GRAND CHEROKEE 2002 WJ / 2.G Repair Manual

STANDARD PROCEDURE - DRAINING COOLING
SYSTEM - 4.0L ENGINE
WARNING: DO NOT REMOVE THE CYLINDER
BLOCK DRAIN PLUGS OR LOOSEN THE RADIATOR
DRAINCOCK WITH SYSTEM HOT AND UNDER
PRESSURE. SERIOUS BURNS FROM COOLANT
CAN OCCUR.
(1) DO NOT remove radiator cap first. With engine
cold, raise vehicle on a hoist and locate radiator
draincock.
NOTE: Radiator draincock is located on the right/
lower side of radiator facing to rear of vehicle.
(2) Attach one end of a hose to the draincock. Put
the other end into a clean container. Open draincock
and drain coolant from radiator. This will empty the
coolant reserve/overflow tank. The coolant does not
have to be removed from the tank unless the system
is being refilled with a fresh mixture. When tank is
empty, remove radiator cap and continue draining
cooling system.
To drain the engine of coolant, remove the cylinder
block drain plug located on the side of cylinder block
(Fig. 9).
STANDARD PROCEDURE - REFILLING
COOLING SYSTEM - 4.0L ENGINE
(1) Tighten the radiator draincock and the cylinder
block drain plug(s) (if removed).
(2) Fill system using a 50/50 mixture of ethylene-
glycol antifreeze and low mineral content water. Fill
radiator to top and install radiator cap. Add suffi-
cient coolant to the reserve/overflow tank to raise
level to FULL mark.
(3) With heater control unit in the HEAT position,
operate engine with radiator cap in place.
(4) After engine has reached normal operating
temperature, shut engine off and allow it to cool.
When engine is cooling down, coolant will be drawn
into the radiator from the reserve/overflow tank.
(5) Add coolant to reserve/overflow tank as neces-
sary.Only add coolant to the reserve/overflow
tank when the engine is cold. Coolant level in a
warm engine will be higher due to thermal
expansion.To purge the cooling system of all air,
this heat up/cool down cycle (adding coolant to cold
engine) must be performed three times. Add neces-
sary coolant to raise tank level to the FULL mark
after each cool down period.
STANDARD PROCEDURE - ADDING
ADDITIONAL COOLANT
The use of aluminum cylinder blocks, cylinder
heads and water pumps requires special corrosion
protection. Only MopartAntifreeze/Coolant, 5
Year/100,000 Mile Formula (glycol base coolant with
Fig. 8 Cooling System Bleed Plug - 4.7L
1 - COOLING SYSTEM BLEED PLUG
Fig. 9 Drain PlugÐ4.0L Engine
1 - COOLANT TEMPERATURE SENSOR
2 - BLOCK DRAIN PLUG
WJCOOLING 7 - 13
COOLING (Continued)

corrosion inhibitors called HOAT, for Hybrid Organic
Additive Technology) is recommended. This coolant
offers the best engine cooling without corrosion when
mixed with 50% distilled water to obtain to obtain a
freeze point of -37ÉC (-35ÉF). If it loses color or
becomes contaminated, drain, flush, and replace with
fresh properly mixed coolant solution.
CAUTION: Do not use coolant additives that are
claimed to improve engine cooling.
STANDARD PROCEDURE - COOLING SYSTEM -
REVERSE FLUSHING
CAUTION: The cooling system normally operates at
97-to-124 kPa (14-to -18 psi) pressure. Exceeding
this pressure may damage the radiator or hoses.
Reverse flushing of the cooling system is the forc-
ing of water through the cooling system. This is done
using air pressure in the opposite direction of normal
coolant flow. It is usually only necessary with very
dirty systems with evidence of partial plugging.
CHEMICAL CLEANING
If visual inspection indicates the formation of
sludge or scaly deposits, use a radiator cleaner
(Mopar Radiator Kleen or equivalent) before flushing.
This will soften scale and other deposits and aid the
flushing operation.
CAUTION: Be sure instructions on the container are
followed.
REVERSE FLUSHING RADIATOR
Disconnect the radiator hoses from the radiator fit-
tings. Attach a section of radiator hose to the radia-
tor bottom outlet fitting and insert the flushing gun.
Connect a water supply hose and air supply hose to
the flushing gun.
CAUTION: The cooling system normally operates at
97-to-124 kPa (14- to-18 psi) pressure. Exceeding
this pressure may damage the radiator or hoses.
Allow the radiator to fill with water. When radiator
is filled, apply air in short blasts allowing radiator to
refill between blasts. Continue this reverse flushing
until clean water flows out through rear of radiator
cooling tube passages. For more information, refer to
operating instructions supplied with flushing equip-
ment. Have radiator cleaned more extensively by a
radiator repair shop.
REVERSE FLUSHING ENGINE
Drain the cooling system (Refer to 7 - COOLING -
STANDARD PROCEDURE). Remove the thermostat
housing and thermostat. Install the thermostat hous-
ing. Disconnect the radiator upper hose from the
radiator and attach the flushing gun to the hose. Dis-
connect the radiator lower hose from the water
pump. Attach a lead away hose to the water pump
inlet fitting.
CAUTION: Be sure that the heater control valve is
closed (heat off). This is done to prevent coolant
flow with scale and other deposits from entering
the heater core.
Connect the water supply hose and air supply hose
to the flushing gun. Allow the engine to fill with
water. When the engine is filled, apply air in short
blasts, allowing the system to fill between air blasts.
Continue until clean water flows through the lead
away hose. For more information, refer to operating
instructions supplied with flushing equipment.
Remove the lead away hose, flushing gun, water
supply hose and air supply hose. Remove the thermo-
stat housing (Refer to 7 - COOLING/ENGINE/EN-
GINE COOLANT THERMOSTAT - REMOVAL).
Install the thermostat and housing with a replace-
ment gasket (Refer to 7 - COOLING/ENGINE/EN-
GINE COOLANT THERMOSTAT -
INSTALLATION). Connect the radiator hoses. Refill
the cooling system with the correct antifreeze/water
mixture (Refer to 7 - COOLING - STANDARD PRO-
CEDURE).
SPECIFICATIONS
TORQUE
DESCRIPTION N´m Ft. In.
Lbs. Lbs.
Automatic Belt Tensioner to
Mounting
BracketÐBolt
4.0L 28 Ð 250
4.7L 41 30 Ð
Automatic Belt Tensioner
PulleyÐ
Bolt
(4.7L) 61 45 Ð
Block HeaterÐBolt
7 - 14 COOLINGWJ
COOLING (Continued)

CONDITION POSSIBLE CAUSES CORRECTION
BELT BROKEN (NOTE: IDENTIFY
AND CORRECT PROBLEM
BEFORE NEW BELT IS
INSTALLED)1. Excessive tension. 1. Replace belt and automatic belt
tensioner.
2. Incorrect belt. 2. Replace belt.
3. Tensile member damaged during
belt installation.3. Replace belt.
4. Severe misalignment. 4. Check and replace.
5. Bracket, pulley, or bearing failure. 5. Replace defective component
and belt.
NOISE (OBJECTIONABLE
SQUEAL, SQUEAK, OR RUMBLE
IS HEARD OR FELT WHILE
DRIVE BELT IS IN OPERATION)1. Belt slippage. 1. Replace belt or automatic belt
tensioner.
2. Bearing noise. 2. Locate and repair.
3. Belt misalignment. 3. Replace belt.
4. Belt-to-pulley mismatch. 4. Install correct belt.
REMOVALÐ4.0L ENGINE
NOTE: The belt routing schematics are published
from the latest information available at the time of
publication. If anything differs between these sche-
matics and the Belt Routing Label, use the sche-
matics on Belt Routing Label. This label is located
in the engine compartment.
CAUTION: DO NOT LET TENSIONER ARM SNAP
BACK TO THE FREEARM POSITION, SEVERE DAM-
AGE MAY OCCUR TO THE TENSIONER.
Belt tension is not adjustable. Belt adjustment is
maintained by an automatic ( spring load ) belt ten-
sioner.
(1) Disconnect negative battery cable from battery.
(2) Rotate belt tensioner until it contacts its stop.
Remove belt, then slowly rotate the tensioner into
the freearm position. (Fig. 4).
INSTALLATIONÐ4.0L ENGINE
NOTE: The belt routing schematics are published
from the latest information available at the time of
publication. If anything differs between these sche-
matics and the Belt Routing Label, use the sche-
matics on Belt Routing Label. This label is located
in the engine compartment.
Belt tension is not adjustable. Belt adjustment is
maintained by an automatic ( spring load ) belt ten-
sioner.
(1) Check condition of all pulleys.CAUTION: When installing the serpentine accessory
drive belt, the belt MUST be routed correctly. If not,
the engine may overheat due to the water pump
rotating in the wrong direction (Fig. 4).
Fig. 4 Belt RoutingÐ4.0L
1 - GENERATOR
2 - IDLER
3 - POWER STEERING
4 - A/C
5 - CRANKSHAFT
6 - WATER PUMP
7 - TENSIONER
8 - ACCESSORY DRIVE BELT
WJACCESSORY DRIVE 7 - 19
DRIVE BELTS - 4.0L (Continued)

CONDITION POSSIBLE CAUSES CORRECTION
BELT BROKEN (NOTE: IDENTIFY
AND CORRECT PROBLEM
BEFORE NEW BELT IS
INSTALLED)1. Excessive tension. 1. Replace belt and automatic belt
tensioner.
2. Incorrect belt. 2. Replace belt.
3. Tensile member damaged during
belt installation.3. Replace belt.
4. Severe misalignment. 4. Check and replace.
5. Bracket, pulley, or bearing failure. 5. Replace defective component
and belt.
NOISE (OBJECTIONABLE
SQUEAL, SQUEAK, OR RUMBLE
IS HEARD OR FELT WHILE
DRIVE BELT IS IN OPERATION)1. Belt slippage. 1. Replace belt or automatic belt
tensioner.
2. Bearing noise. 2. Locate and repair.
3. Belt misalignment. 3. Replace belt.
4. Belt-to-pulley mismatch. 4. Install correct belt.
REMOVAL - 4.7L ENGINE
NOTE: The belt routing schematics are published
from the latest information available at the time of
publication. If anything differs between these sche-
matics and the Belt Routing Label, use the sche-
matics on Belt Routing Label. This label is located
in the engine compartment.
CAUTION: DO NOT LET TENSIONER ARM SNAP
BACK TO THE FREEARM POSITION, SEVERE DAM-
AGE MAY OCCUR TO THE TENSIONER.
Belt tension is not adjustable. Belt adjustment is
maintained by an automatic ( spring load ) belt ten-
sioner.
(1) Disconnect negative battery cable from battery.
(2) Rotate belt tensioner until it contacts its stop.
Remove belt, then slowly rotate the tensioner into
the freearm position. (Fig. 7).
Fig. 7 Belt Routing - 4.7L
1 - GENERATOR PULLEY
2 - ACCESSORY DRIVE BELT
3 - POWER STEERING PUMP PULLEY
4 - CRANKSHAFT PULLEY
5 - IDLER PULLEY
6 - TENSIONER
7 - A/C COMPRESSOR PULLEY
8 - WATER PUMP PULLEY
7 - 22 ACCESSORY DRIVEWJ
DRIVE BELTS - 4.7L (Continued)

INSPECTION..........................52
INSTALLATION.........................52
RADIATOR PRESSURE CAP
DESCRIPTION.........................53
OPERATION...........................53
DIAGNOSIS AND TESTINGÐRADIATOR
PRESSURE CAP......................53CLEANING............................53
INSPECTION..........................54
WATER PUMP INLET TUBE
REMOVAL.............................54
INSTALLATION.........................54
COOLANT
DESCRIPTION
DESCRIPTION - ENGINE COOLANT
ETHYLENE-GLYCOL MIXTURES
CAUTION: Richer antifreeze mixtures cannot be
measured with normal field equipment and can
cause problems associated with 100 percent ethyl-
ene-glycol.
The required ethylene-glycol (antifreeze) and water
mixture depends upon the climate and vehicle oper-
ating conditions. The recommended mixture of 50/50
ethylene-glycol and water will provide protection
against freezing to -37 deg. C (-35 deg. F). The anti-
freeze concentrationmust alwaysbe a minimum of
44 percent, year-round in all climates.If percentage
is lower than 44 percent, engine parts may be
eroded by cavitation, and cooling system com-
ponents may be severely damaged by corrosion.
Maximum protection against freezing is provided
with a 68 percent antifreeze concentration, which
prevents freezing down to -67.7 deg. C (-90 deg. F). A
higher percentage will freeze at a warmer tempera-
ture. Also, a higher percentage of antifreeze can
cause the engine to overheat because the specific
heat of antifreeze is lower than that of water.
Use of 100 percent ethylene-glycol will cause for-
mation of additive deposits in the system, as the cor-
rosion inhibitive additives in ethylene-glycol require
the presence of water to dissolve. The deposits act as
insulation, causing temperatures to rise to as high as
149 deg. C (300) deg. F). This temperature is hot
enough to melt plastic and soften solder. The
increased temperature can result in engine detona-
tion. In addition, 100 percent ethylene-glycol freezes
at 22 deg. C (-8 deg. F ).
PROPYLENE-GLYCOL MIXTURES
It's overall effective temperature range is smaller
than that of ethylene-glycol. The freeze point of 50/50
propylene-glycol and water is -32 deg. C (-26 deg. F).
5 deg. C higher than ethylene-glycol's freeze point.
The boiling point (protection against summer boil-
over) of propylene-glycol is 125 deg. C (257 deg. F )at 96.5 kPa (14 psi), compared to 128 deg. C (263
deg. F) for ethylene-glycol. Use of propylene-glycol
can result in boil-over or freeze-up on a cooling sys-
tem designed for ethylene-glycol. Propylene glycol
also has poorer heat transfer characteristics than
ethylene glycol. This can increase cylinder head tem-
peratures under certain conditions.
Propylene-glycol/ethylene-glycol Mixtures can
cause the destabilization of various corrosion inhibi-
tors, causing damage to the various cooling system
components. Also, once ethylene-glycol and propy-
lene-glycol based coolants are mixed in the vehicle,
conventional methods of determining freeze point will
not be accurate. Both the refractive index and spe-
cific gravity differ between ethylene glycol and propy-
lene glycol.
DESCRIPTION - HOAT COOLANT
WARNING: ANTIFREEZE IS AN ETHYLENE GLYCOL
BASE COOLANT AND IS HARMFUL IF SWAL-
LOWED OR INHALED. IF SWALLOWED, DRINK
TWO GLASSES OF WATER AND INDUCE VOMIT-
ING. IF INHALED, MOVE TO FRESH AIR AREA.
SEEK MEDICAL ATTENTION IMMEDIATELY. DO NOT
STORE IN OPEN OR UNMARKED CONTAINERS.
WASH SKIN AND CLOTHING THOROUGHLY AFTER
COMING IN CONTACT WITH ETHYLENE GLYCOL.
KEEP OUT OF REACH OF CHILDREN. DISPOSE OF
GLYCOL BASE COOLANT PROPERLY, CONTACT
YOUR DEALER OR GOVERNMENT AGENCY FOR
LOCATION OF COLLECTION CENTER IN YOUR
AREA. DO NOT OPEN A COOLING SYSTEM WHEN
THE ENGINE IS AT OPERATING TEMPERATURE OR
HOT UNDER PRESSURE, PERSONAL INJURY CAN
RESULT. AVOID RADIATOR COOLING FAN WHEN
ENGINE COMPARTMENT RELATED SERVICE IS
PERFORMED, PERSONAL INJURY CAN RESULT.
CAUTION: Use of Propylene Glycol based coolants
is not recommended, as they provide less freeze
protection and less corrosion protection.
The cooling system is designed around the coolant.
The coolant must accept heat from engine metal, in
the cylinder head area near the exhaust valves and
engine block. Then coolant carries the heat to the
radiator where the tube/fin radiator can transfer the
heat to the air.
WJENGINE 7 - 25

(1) Position sensor into the coolant recovery pres-
sure container (Fig. 1).
(2) Connect the coolant level sensor electrical con-
nector (Fig. 2).
(3) Close hood.
COOLANT RECOVERY PRESS
CONTAINER
DESCRIPTION
This system works along with the radiator pres-
sure cap. This is done by using thermal expansion
and contraction of the coolant to keep the coolant
free of trapped air. It provides:
²A volume for coolant expansion and contraction.
²A convenient and safe method for checking/ad-
justing coolant level at atmospheric pressure. This is
done without removing the radiator pressure cap.
²Some reserve coolant to the radiator to cover
minor leaks and evaporation or boiling losses.
As the engine cools, a vacuum is formed in the
cooling system of both the radiator and engine. Cool-
ant will then be drawn from the coolant tank and
returned to a proper level in the radiator.
The coolant reservoir/overflow system has a radia-
tor mounted pressurized cap, an overflow tube and a
plastic coolant reservoir/overflow tank (Fig. 3)
mounted to the right inner fender.
RADIATOR FAN - 4.7L
DESCRIPTION
The hydraulic fan (Fig. 4) used on vehicles
equipped the 4.7L engine, replaces both the electric
fan and the engine driven mechanical fan. The
hydraulic cooling fan is integral to the fan shroud
and is located between the radiator and the engine.
The power steering pump supplies the hydraulic
fluid and pressure to rotate the cooling fan blade,
while the electrical part of the fan is controlled by
the JTEC.
The hydraulic fan drive (motor) consists of the
three major following components:
²Steering flow control valve
Fig. 1 COOLANT LEVEL SENSOR ELECTRICAL
CONNECTOR
Fig. 2 COOLANT LEVEL SENSOR REMOVAL/
INSTALLATION
Fig. 3 Coolant Reservoir / Overflow Tank
1 - COOLANT OVERFLOW HOSE
2 - COOLANT RESERVOIR/OVERFLOW TANK
3 - COOLANT LEVEL SENSOR
4 - BOLT
WJENGINE 7 - 27
COOLANT LEVEL SENSOR (Continued)

²Fan control valve
²Two stage G-rotor hydraulic drive
The hydraulic fan and drive is not serviceable.
Therefore any failure of the fan blade, hydraulic fan
drive or fan shroud requires replacement of the fan
module because the fan blade and hydraulic fan drive
are matched and balanced as a system and servicing
either separately would disrupt this balance.
For hydraulic fluid routing information refer to
(Fig. 5).
CAUTION: Do not attempt to service the hydraulic
cooling fan or fan drive separately replace the cooling
module as an assembly. Failure to do so may cause
severe damage to the hydraulic cooling fan assembly.
OPERATION
The hydraulic radiator cooling fan used on the
Grand Cherokee with the 4.7L engine replaces both
the electric fan and the engine driven mechanical
fan. The use of this hydraulic fan provides the 4.7L
equipped Grand Cherokee with heavy trailer tow
capability while at the same time reducing unneces-
sary power drain on both the engine and the vehicles
electrical system.
HYDRAULIC FAN STRATEGY
The hydraulic radiator cooling fan is controlled by
the JTEC. A PWM (Pulse With Modulated) signal
from the JTEC controls the fan from 0 to 100% of the
available fan speed. There are four inputs to the
JTEC that determine what speed percentage of fan is
required by the vehicle. These inputs are:
²Engine Coolant Temperature
²Transmission Oil Temperature
²Battery Temperature
²A/C System Pressure
By monitoring these four parameters, the JTEC
can determine if cooling airflow is required. If airflow
is required, the JTEC will slowly ramp up (speed up)
the fan speed until the parameter(s) are under con-
trol. Once the temperature or pressure is reduced to
within operating parameters the fan will ramp up,
ramp down, or hold its speed to maintain the temper-
ature / pressure requirements.
NOTE: Even if the JTEC is not requesting fan on
operation the fan blade will usually spin between
100 and 500 RPM when the vehicle is at idle. This is
due to a controlled minimum oil flow requirement
through the fan drive motor.
ACTIVATING THE HYDRAULIC FAN WITH THE DRB
Under the Engine Systems test heading, there is a
subheading. ªHydraulic fan solenoid testº, that has
the selections, on /off. Activating the fan with the
DRB will run the fan at 100% duty cycle, which will
help troubleshoot any system problems, and also help
with the deaeration procedure.
NOTE: Engine must be running to activate the fan
with the DRB.
RADIATOR COOLING FAN HYDRAULIC FLUID PATH
Hydraulic fluid is pumped through the power
steering pump, from the pump the fluid travels
though a high pressure delivery line to the fan drive
motor. As fluid is diverted through the G-rotors, rota-
tional motion is created as fluid moves from the high-
pressure (inlet) side of the motor to the low-pressure
(outlet) side. Fluid exiting the drive motor is divided
into two paths. Path one continues through a high
pressure delivery line to the vehicles steering gear to
provide steering assist. and path two sends fluid
back to the power steering pump through a low pres-
sure line. Fluid exits the steering gear under low
pressure and travels through a low pressure line to
the power steering fluid cooler to be cooled before
being returned back the the power steering fluid res-
ervoir (Fig. 5).
Fig. 4 HYDRAULIC RADIATOR COOLING FAN AND
FAN DRIVE
1 - POWER STEERING FLUID COOLER
2 - RADIATOR
3 - HIGH PRESSURE LINE FROM STEERING GEAR PUMP TO
HYDRAULIC FAN MOTOR
4 - HYDRAULIC FAN MOTOR
5 - HIGH PRESSURE LINE FROM HYDRAULIC FAN MOTOR TO
STEERING GEAR
6 - FAN SHROUD
7 - 28 ENGINEWJ
RADIATOR FAN - 4.7L (Continued)

NOTE: When ever the high pressure line fittings are
removed from the hydraulic fan drive the o-rings
located on the fittings must be replaced.
(7) Lubricate the o-rings on the fittings with power
steering fluid then connect inlet and outlet high pres-
sure lines to fan drive (Fig. 9). Tighten inlet line to
49 N´m (36 ft. lbs.) tighten outlet line to 29 N´m (21.5
ft. lbs.).
(8) Connect low pressure return hose to fan drive
(Fig. 9).
(9) Lower vehicle.
(10) Install radiator upper hose.
(11) Connect electrical connector for hydraulic fan
control solenoid.
(12) Tighten fan shroud upper mounting bolts to 6
N´m (50 in. lbs.).
(13) Refill cooling system (Refer to 7 - COOLING -
STANDARD PROCEDURE).
CAUTION: Do not run engine with power steering
fluid below the full mark in the reservoir. Sever
damage to the hydraulic cooling fan or the engine
can occur.(14) Refill power steering fluid reservoir and bleed
air from steering system (Refer to 19 - STEERING/
PUMP - STANDARD PROCEDURE).
(15) Run engine and check for leaks.
RADIATOR FAN - 4.0L
DESCRIPTION
The radiator cooling fan used on the 4.0L engine is
an hybrid fan design. The hybrid fan system consist
of a low speed viscous driven mechanical fan and a
electrical fan (Fig. 10).
REMOVAL
(1) Disconnect negative battery cable from battery.
(2) The thermal viscous fan drive/fan blade assem-
bly is attached (threaded) to water pump hub shaft.
Remove fan blade/viscous fan drive assembly from
water pump by turning mounting nut counterclock-
wise as viewed from front (Fig. 11). Threads on vis-
cous fan drive areRIGHT HAND.
(3) Do not attempt to remove fan/viscous fan drive
assembly from vehicle at this time.
(4) Do not unbolt fan blade assembly from viscous
fan drive at this time.
(5) Remove fan shroud-to-upper crossmember nuts.
(6) Remove fan shroud and fan blade/viscous fan
drive assembly as a complete unit from vehicle.
Fig. 9 HYDRAULIC LINES/HOSES AND ELECTRICAL
CONNECTOR
1 - LOW PRESSURE RETURN HOSE
2 - HIGH PRESSURE LINE (OUTLET)
3 - HIGH PRESSURE LINE (INLET)
4 - HYDRAULIC FAN DRIVEFig. 10 Radiator Cooling Fan
1 - RADIATOR
2 - ELECTRIC COOLING FAN CONNECTOR
3 - FAN SHROUD
4 - ELECTRIC COOLING FAN
WJENGINE 7 - 31
RADIATOR FAN - 4.7L (Continued)

(2) Insert block heater assembly with element loop
pointing at twelve o'clock (Fig. 19).
(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 TEMP
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:
²for engine coolant temperature gauge operation
through CCD or PCI (J1850) communications
²Injector pulse-width
²Spark-advance curves
²ASD relay shut-down times
²Idle Air Control (IAC) motor key-on steps
²Pulse-width prime-shot during cranking
²O2 sensor closed loop times
²Purge solenoid on/off times
²EGR solenoid on/off times (if equipped)
²Leak Detection Pump operation (if equipped)
²Radiator fan relay on/off times (if equipped)
²Target idle speed
REMOVAL
REMOVALÐ4.0L ENGINE
WARNING: HOT, PRESSURIZED COOLANT CAN
CAUSE INJURY BY SCALDING. COOLING SYSTEM
MUST BE PARTIALLY DRAINED BEFORE REMOV-
ING THE ENGINE COOLANT TEMPERATURE (ECT)
SENSOR. REFER TO GROUP 7, COOLING.
(1) Partially drain cooling system. (Refer to 7 -
COOLING - STANDARD PROCEDURE).
Fig. 18 Drain Plug
1 - COOLANT TEMPERATURE SENSOR
2 - BLOCK DRAIN PLUG
Fig. 19 Engine Block Heater
1 - ENGINE BLOCK HEATER
WJENGINE 7 - 35
ENGINE BLOCK HEATER (Continued)

REMOVAL
REMOVALÐ4.0L ENGINE
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) Drain the coolant from the radiator until the
level is below the thermostat housing (Refer to 7 -
COOLING - STANDARD PROCEDURE).
WARNING: CONSTANT TENSION HOSE CLAMPS
ARE USED ON MOST COOLING SYSTEM HOSES.
WHEN REMOVING OR INSTALLING, USE ONLY
TOOLS DESIGNED FOR SERVICING THIS TYPE OF
CLAMP, SUCH AS SPECIAL CLAMP TOOL (NUMBER
6094) (Fig. 52). SNAP-ON CLAMP TOOL (NUMBER
HPC-20) MAY BE USED FOR LARGER CLAMPS.
ALWAYS WEAR SAFETY GLASSES WHEN SERVIC-
ING CONSTANT TENSION CLAMPS.
CAUTION: A number or letter is stamped into the
tongue of constant tension clamps. If replacement
is necessary, use only an original equipment clamp
with matching number or letter.
(2) Remove radiator upper hose and heater hose at
thermostat housing.
(3) Disconnect wiring connector at engine coolant
temperature sensor.
(4) Remove thermostat housing mounting bolts,
thermostat housing, gasket and thermostat (Fig. 24).
Discard old gasket.
(5) Clean the gasket mating surfaces.
REMOVALÐ4.7L ENGINE
WARNING: DO NOT LOOSEN RADIATOR DRAIN-
COCK WITH SYSTEM HOT AND PRESSURIZED.
SERIOUS BURNS FROM COOLANT CAN OCCUR.
Do not waste reusable coolant. If solution is clean,
drain coolant into a clean container for reuse.
If thermostat is being replaced, be sure that
replacement is specified thermostat for vehicle model
and engine type.
(1) Disconnect negative battery cable at battery.
(2) Drain cooling system (Refer to 7 - COOLING -
STANDARD PROCEDURE).
(3) Raise vehicle on hoist.
(4) Remove splash shield.(5) Remove lower radiator hose clamp and lower
radiator hose at thermostat housing.
(6) Remove thermostat housing mounting bolts,
thermostat housing and thermostat (Fig. 25).
INSTALLATION
INSTALLATIONÐ4.0L ENGINE
(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. 26).
(b) Position thermostat in 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 22 N´m (16 ft. lbs.)
torque.
(4) Install hoses to thermostat housing.
Fig. 24 Thermostat
1 - LONG BOLT
2 - GASKET
3 - THERMOSTAT
4 - THERMOSTAT HOUSING
5 - SHORT BOLT
7 - 38 ENGINEWJ
ENGINE COOLANT THERMOSTAT (Continued)