2002 JEEP GRAND CHEROKEE engine

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 other prob-
lems. These are: longer engine warmup time, unreli-
able warmup performance, increased exhaust
emissions and crankcase condensation. This conden-
sation can result in sludge formation.
DESCRIPTIONÐ4.0L ENGINE
CAUTION: Do not operate an engine without a ther-
mostat, except for servicing or testing.
A pellet-type thermostat controls the operating
temperature of the engine by controlling the amount
of coolant flow to the radiator. On all engines the
thermostat is closed below 195ÉF (90ÉC). Above this
temperature, coolant is allowed to flow to the radia-
tor. This provides quick engine warm up and overall
temperature control. (Fig. 23).
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 other prob-
lems. These are: longer engine warmup time, unreli-
able warmup performance, increased exhaust
emissions and crankcase condensation. This conden-
sation 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 TESTINGÐTHERMOSTAT
ON-BOARD DIAGNOSTICS
All models are equipped with On-Board Diagnos-
tics for certain cooling system components.If the pow-
ertrain control module (PCM) detects low engine
coolant temperature, it will record a Diagnostic Trou-
ble Code (DTC). For other DTC numbers, (Refer to 25
- EMISSIONS CONTROL - DESCRIPTION).
The DTC can also be accessed through the DRB
scan tool.
Fig. 22 Thermostat
1 - FROM HEATER
2 - FROM RADIATOR
3 - TO WATER PUMP
4 - ENGINE BYPASS
5 - THERMOSTAT
Fig. 23 Thermostat and Housing
1 - LONG BOLT
2 - GASKET
3 - THERMOSTAT
4 - THERMOSTAT HOUSING
5 - SHORT BOLT
WJENGINE 7 - 37
ENGINE COOLANT THERMOSTAT (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)

(5) Install electrical connector to coolant tempera-
ture sensor.
(6) Be sure that the radiator draincock is tightly
closed. Fill the cooling system to the correct levelwith the required coolant mixture (Refer to 7 -
COOLING - STANDARD PROCEDURE).
(7) Start and warm the engine. Check for leaks.
INSTALLATIONÐ4.7L ENGINE
(1) Clean mating areas of timing chain cover and
thermostat housing.
(2) Install thermostat (spring side down) into
recessed machined groove on timing chain cover (Fig.
25).
(3) Position thermostat housing on timing chain
cover.
(4) Install two housing-to-timing chain cover bolts.
Tighten bolts to 13 N´m (115 in. lbs.) torque.
CAUTION: Housing must be tightened evenly and
thermostat must be centered into recessed groove
in timimg chain cover. If not, it may result in a
cracked housing, damaged timing chain cover
threads or coolant leaks.
(5) Install lower radiator hose on thermostat hous-
ing.
(6) Install splash shield.
(7) Lower vehicle.
(8) Fill cooling system (Refer to 7 - COOLING -
STANDARD PROCEDURE).
(9) Connect negative battery cable to battery.
(10) Start and warm the engine. Check for leaks.
Fig. 25 Thermostat and Thermostat Housing
1 - THERMOSTAT HOUSING
2 - THERMOSTAT LOCATION3 - THERMOSTAT AND GASKET
4 - TIMING CHAIN COVER
Fig. 26 Thermostat Recess
1 - GROOVE
WJENGINE 7 - 39
ENGINE COOLANT THERMOSTAT (Continued)

FAN DRIVE VISCOUS CLUTCH
- 4.0L
DESCRIPTION
CAUTION: Engines equipped with serpentine drive
belts have reverse rotating fans and viscous fan
drives. They are marked with the word REVERSE to
designate their usage. Installation of the wrong fan
or viscous fan drive can result in engine overheat-
ing.
CAUTION: If the viscous fan drive is replaced
because of mechanical damage, the cooling fan
blades should also be inspected. Inspect for fatigue
cracks, loose blades, or loose rivets that could
have resulted from excessive vibration. Replace fan
blade assembly if any of these conditions are
found. Also inspect water pump bearing and shaft
assembly for any related damage due to a viscous
fan drive malfunction.
The thermal viscous fan drive (Fig. 27) is a sili-
cone-fluid-filled coupling used to connect the fan
blades to the water pump shaft. The coupling allows
the fan to be driven in a normal manner. This is
done at low engine speeds while limiting the top
speed of the fan to a predetermined maximum level
at higher engine speeds.
An electrical cooling fan located in the fan shroud
aids in low speed cooling, It is designed to augment
the viscous fan, However, it does not replace the vis-
cous fan.
OPERATION
A thermostatic bimetallic spring coil is located on
the front face of the viscous fan drive unit (Fig. 27).
This spring coil reacts to the temperature of the radi-
ator discharge air. It engages the viscous fan drive
for higher fan speed if the air temperature from the
radiator rises above a certain point. Until additional
engine cooling is necessary,the fan will remain at
a reduced rpm regardless of engine speed. Nor-
mally less than three hundred (300) rpm.
Only when sufficient heat is present, will the vis-
cous fan drive engage. This is when the air flowing
through the radiator core causes a reaction to the
bimetallic coil. It then increases fan speed to provide
the necessary additional engine cooling.
Once the engine has cooled, the radiator discharge
temperature will drop. The bimetallic coil again
reacts and the fan speed is reduced to the previous
disengaged speed.
DIAGNOSIS AND TESTINGÐVISCOUS FAN
DRIVE
If the fan assembly free-wheels without drag (the
fan blades will revolve more than five turns when
spun by hand), replace the fan drive. This spin test
must be performed when the engine is cool.
For the following test, the cooling system must be
in good condition. It also will ensure against exces-
sively high coolant temperature.
WARNING: BE SURE THAT THERE IS ADEQUATE
FAN BLADE CLEARANCE BEFORE DRILLING.
(1) Drill a 3.18-mm (1/8-in) diameter hole in the
top center of the fan shroud.
(2) Obtain a dial thermometer with an 8 inch stem
(or equivalent). It should have a range of -18É to
105ÉC (0É to 220É F). Insert thermometer through the
hole in the shroud. Be sure that there is adequate
clearance from the fan blades.
(3) Connect a tachometer and an engine ignition
timing light (timing light is to be used as a strobe
light).
(4) Block the air flow through the radiator. Secure
a sheet of plastic in front of the radiator (or air con-
ditioner condenser). Use tape at the top to secure the
plastic and be sure that the air flow is blocked.
(5) Be sure that the air conditioner (if equipped) is
turned off.
WARNING: USE EXTREME CAUTION WHEN THE
ENGINE IS OPERATING. DO NOT STAND IN A
DIRECT LINE WITH THE FAN. DO NOT PUT YOUR
HANDS NEAR THE PULLEYS, BELTS OR FAN. DO
NOT WEAR LOOSE CLOTHING.
Fig. 27 Viscous Fan Drive
1 - VISCOUS FAN DRIVE
2 - THERMOSTATIC SPRING
3 - MOUNTING NUT TO WATER PUMP HUB
7 - 40 ENGINEWJ

(6) Start the engine and operate at 2400 rpm.
Within ten minutes the air temperature (indicated on
the dial thermometer) should be up to 93É C (200É F).
Fan driveengagementshould have started to occur
at between 91É to 96É C (195É to 205É F). Engage-
ment is distinguishable by a definiteincreasein fan
flow noise (roaring). The timing light also will indi-
cate an increase in the speed of the fan.
(7) When the air temperature reaches 93É C (200É
F), remove the plastic sheet. Fan drivedisengage-
mentshould have started to occur at between 62É to
85É C (145É to 185É F). A definitedecreaseof fan
flow noise (roaring) should be noticed. If not, replace
the defective viscous fan drive unit.
PWM FAN CONTROL MODULE -
4.0L
DESCRIPTION
The pulse width modulated (PWM) radiator cooling
fan relay is located behind the front bumper fascia
below the right headlamp.
OPERATION
The PWM relay is used to control the speed of the
electric radiator cooling fan. It allows for multiple fan
speeds. This allows for improved fan noise and A/C
performance, better engine cooling, and additional
vehicle power.
PWM relay operation is controlled by the Power-
train Control Module (PCM). To operate the PWM
relay, the PCM looks at inputs from:
²Engine coolant temperature
²Ambient temperature from the body controller
²Vehicle speed
²Transmission oil temperature
²A/C switch position (A/C request)
REMOVAL
The Pulse Width Modulated (PWM) cooling fan
relay is located below the right headlamp behind the
bumper fascia (Fig. 28).
(1) Remove front bumper and grill assembly.
(2) Remove 1 support bolt near front of reservoir
(Fig. 28).
(3) Remove 2 reservoir mounting bolts.
(4) Remove reservoir from vehicle to gain access to
vacuum hose (Fig. 29). Disconnect vacuum hose from
reservoir fitting at rear of reservoir.
(5) Disconnect electrical connector at relay (Fig.
30).
(6) Remove 2 relay mounting bolts (Fig. 30) and
remove relay.
Fig. 28 Radiator Cooling Fan Relay Location
1 - RADIATOR FAN RELAY
2 - VACUUM RESERVOIR
3 - BOLT
4 - RIGHT FRONT FENDER
Fig. 29 Vacuum Reservoir Removal/Installation
1 - VACUUM HOSE
2 - RADIATOR
3 - VACUUM RESERVOIR
WJENGINE 7 - 41
FAN DRIVE VISCOUS CLUTCH - 4.0L (Continued)

INSTALLATION
(1) Position relay to body and install 2 bolts.
Tighten bolts to 3 N´m (25 in. lbs.) torque.
(2) Connect electrical connector to relay.
(3) Connect vacuum hose to reservoir.
(4) Install reservoir and tighten 2 bolts to 3 N´m
(25 in. lbs.) torque.
(5) Install front bumper and grill assembly.
RADIATOR - 4.7L
DESCRIPTION
All vehicles are equipped with a cross flow type
radiator with plastic side tanks (Fig. 31).
Plastic tanks, while stronger than brass, are sub-
ject to damage by impact, such as from tools or
wrenches. Handle radiator with care.
REMOVAL
WARNING: DO NOT REMOVE THE CYLINDER
BLOCK DRAIN PLUGS OR LOOSEN THE RADIATOR
DRAINCOCK WITH THE SYSTEM HOT AND UNDER
PRESSURE. SERIOUS BURNS FROM COOLANT
CAN OCCUR. REFER TO COOLING SYSTEM DRAIN-
ING.Do not waste reusable coolant. If the solution is
clean, drain the coolant into a clean container for
reuse.
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. 32). 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 (Fig. 33). If
replacement is necessary, use only an original
equipment clamp with matching number or letter.
CAUTION: When removing the radiator or A/C con-
denser for any reason, note the location of all radi-
ator-to-body and radiator-to-A/C condenser rubber
air seals (Fig. 34). These are used at the top, bot-
tom and sides of the radiator and A/C condenser.
To prevent overheating, these seals must be
installed to their original positions.
(1) Disconnect the negative battery cable at bat-
tery.
(2) Drain coolant from radiator (Refer to 7 -
COOLING - STANDARD PROCEDURE).
(3) Remove the front grill (Refer to 23 - BODY/EX-
TERIOR/GRILLE - REMOVAL).
Fig. 30 Radiator Cooling Fan Relay Removal/
Installation
1 - ELECTRICAL CONNECTOR
2 - RADIATOR FAN RELAY
3 - MOUNTING BOLTS (2)
Fig. 31 Cross Flow Radiator - Typical
1 - RADIATOR
7 - 42 ENGINEWJ
PWM FAN CONTROL MODULE - 4.0L (Continued)

(4) Remove two radiator mounting bolts.
(5) Disconnect both transmission cooler lines from
radiator.
(6) Disconnect electrical connector for the fan con-
trol solenoid.
(7) Disconnect the power steering cooler line from
cooler and filter.
(8) Disconnect the radiator upper and lower hoses.
(9) Disconnect the overflow hose from radiator.
(10) Remove the air inlet duct at the grill.(11) The lower part of radiator is equipped with
two alignment dowel pins (Fig. 35). They are located
on the bottom of radiator tank and fit into rubber
grommets. These rubber grommets are pressed into
the radiator lower crossmember.
WARNING: THE AIR CONDITIONING SYSTEM (IF
EQUIPPED) IS UNDER A CONSTANT PRESSURE
EVEN WITH THE ENGINE OFF. REFER TO REFRIG-
ERANT WARNINGS IN, HEATING AND AIR CONDI-
TIONING BEFORE HANDLING ANY AIR
CONDITIONING COMPONENT.
NOTE: The radiator and radiator cooling fan can be
removed as an assembly. It is not necessary to
remove the cooling fan before removing or install-
ing the radiator.
(12) Disconnect the two high pressure fluid lines
at the hydraulic fan drive.
(13) Disconnect the low pressure return hose at
the hydraulic fan drive.
(14) Gently lift up and remove radiator from vehi-
cle. Be careful not to scrape the radiator fins against
any other component. Also be careful not to disturb
the air conditioning condenser (if equipped).
CLEANING
Clean radiator fins With the engine cold, apply cold
water and compressed air to the back (engine side) of
Fig. 32 Hose Clamp Tool - Typical
1 - HOSE CLAMP TOOL 6094
2 - HOSE CLAMP
Fig. 33 Clamp Number/Letter Location - Typical
1 - TYPICAL CONSTANT TENSION HOSE CLAMP
2 - CLAMP NUMBER/LETTER LOCATION
3 - TYPICAL HOSE
Fig. 34 Air Seals - Typical
1 - AIR DAM
2 - RADIATOR
3 - AIR DAM
4 - A/C CONDENSER
5 - AIR SEAL
WJENGINE 7 - 43
RADIATOR - 4.7L (Continued)

the radiator to flush the radiator and/or A/C con-
denser of debris.
INSPECTION
The radiator cooling fins should be checked for
damage or deterioration. Inspect cooling fins to make
sure they are not bent or crushed, these areas result
in reduced heat exchange causing the cooling system
to operate at higher temperatures. Inspect the plastic
end tanks for cracks, damage or leaks.
Inspect the radiator neck for damage or distortion.
INSTALLATION
CAUTION: Before installing the radiator or A/C con-
denser, be sure the radiator-to-body and radiator-to-
A/C condenser rubber air seals (Fig. 39) are
properly fastened to their original positions. These
are used at the top, bottom and sides of the radia-
tor and A/C condenser. To prevent overheating,
these seals must be installed to their original posi-
tions.
(1) Equipped with air conditioning: Gently lower
the radiator and fan shroud into the vehicle. Guide
the two radiator alignment dowels through the holes
in the rubber air seals first and then through the A/C
support brackets (Fig. 40). Continue to guide thealignment dowels into the rubber grommets located
in lower radiator crossmember. The holes in the
L-shaped brackets (located on bottom of A/C con-
denser) must be positioned between bottom of rubber
air seals and top of rubber grommets.
(2) Connect the radiator upper and lower hoses
and hose clamps to radiator.
CAUTION: The tangs on the hose clamps must be
positioned straight down.
(3) Install coolant reserve/overflow tank hose at
radiator.
(4) Connect both transmission cooler lines at the
radiator.
(5) Install both radiator mounting bolts.
(6) Install air inlet duct at grill.
(7) Attach electric connector for hydraulic fan con-
trol solenoid.
(8) Install the grill (Refer to 23 - BODY/EXTERI-
OR/GRILLE - INSTALLATION).
(9) Connect the two high pressure lines to the
hydraulic fan drive. Tighten
1¤2in. pressure line fit-
ting to 49 N´m (36 ft. lbs.). and the 3/8 in. pressure
line fitting to 29 N´m (21.5 ft. lbs.).
(10) Connect the low pressure hose to the hydrau-
lic fan drive. Position the spring clamp.
(11) Connect the power steering filter hoses to the
filter. Install new hose clamps.
(12) Rotate the fan blades (by hand) and check for
interference at fan shroud.
(13) Refill cooling system (Refer to 7 - COOLING -
STANDARD PROCEDURE).
(14) Refill the power steering reservoir and bleed
air from system (Refer to 19 - STEERING/PUMP -
STANDARD PROCEDURE).
(15) Connect battery cable at battery.
(16) Start and warm engine. Check for leaks.
RADIATOR - 4.0L
DESCRIPTION
All vehicles are equipped with a cross flow type
radiator with plastic side tanks (Fig. 36).
Plastic tanks, while stronger than brass, are sub-
ject to damage by impact, such as from tools or
wrenches. Handle radiator with care.
REMOVAL
WARNING: DO NOT REMOVE THE CYLINDER
BLOCK DRAIN PLUGS OR LOOSEN THE RADIATOR
DRAINCOCK WITH THE SYSTEM HOT AND UNDER
PRESSURE. SERIOUS BURNS FROM COOLANT
CAN OCCUR. REFER TO COOLING SYSTEM DRAIN-
ING.
Fig. 35 Radiator Alignment Dowels - Typical
1 - RADIATOR
2 - ALIGNMENT DOWEL
3 - RADIATOR LOWER ISOLATOR
4 - RADIATOR LOWER CROSSMEMBER
7 - 44 ENGINEWJ
RADIATOR - 4.7L (Continued)