cooling system flow DODGE RAM 2003 Service User Guide

CONDITION POSSIBLE CAUSES CORRECTION
Temperature gauge reading is
inconsistent (flucttuates, cycles
or is erratic)1. During cold weather
operation, with the heater blower
in the high position, the gauge
reading may drop slightly.1. A normal condition. No correction
necessary.
2. Temperature gauge or engine
mounted gauge sensor defective
or shorted. Also, corroded or
loose wiring in this circuit.2. Check operation of gauge and repair if
necessary. (Refer to 8 - ELECTRICAL/
INSTRUMENT CLUSTER - DIAGNOSIS
AND TESTING).
3. Gauge reading rises when
vehicle is brought to a stop after
heavy use (engine still running)3. A normal condition. No correction is
necessary. Gauge should return to normal
range after vehicle is driven.
4. Gauge reading high after
re-starting a warmed up (hot)
engine.4. A normal condition. No correction is
necessary. The gauge should return to
normal range after a few minutes of
engine operation.
5. Coolant level low in radiator
(air will build up in the cooling
system causing the thermostat
to open late).5. Check and correct coolant leaks. (Refer
to 7 - COOLING - DIAGNOSIS AND
TESTING).
6. Cylinder head gasket leaking
allowing exhaust gas to enter
cooling system causing a
thermostat to open late.6. (a) Check for cylinder head gasket
leaks. (Refer to 7 - COOLING -
DIAGNOSIS AND TESTING).
(b) Check for coolant in the engine oil.
Inspect for white steam emitting from the
exhaust system. Repair as necessary.
7. Water pump impeller loose on
shaft.7. Check water pump and replace as
necessary. (Refer to 7 - COOLING/
ENGINE/WATER PUMP - REMOVAL).
8. Loose accessory drive belt.
(water pump slipping)8. (Refer to 7 - COOLING/ACCESSORY
DRIVE/DRIVE BELTS - DIAGNOSIS AND
TESTING). Check and correct as
necessary.
9. Air leak on the suction side of
the water pump allows air to
build up in cooling system
causing thermostat to open late.9. Locate leak and repair as necessary.
PRESSURE CAP IS BLOWING
OFF STEAM AND/OR
COOLANT TO COOLANT TANK.
TEMPERATURE GAUGE
READING MAY BE ABOVE
NORMAL BUT NOT HIGH.
COOLANT LEVEL MAY BE
HIGH IN COOLANT RESERVE/
OVERFLOW TANK1. Pressure relief valve in
radiator cap is defective.1. Check condition of radiator cap and cap
seals. (Refer to 7 - COOLING/ENGINE/
RADIATOR PRESSURE CAP -
DIAGNOSIS AND TESTING). Replace cap
as necessary.
COOLANT LOSS TO THE
GROUND WITHOUT
PRESSURE CAP BLOWOFF.
GAUGE READING HIGH OR
HOT1. Coolant leaks in radiator,
cooling system hoses, water
pump or engine.1. Pressure test and repair as necessary.
(Refer to 7 - COOLING - DIAGNOSIS
AND TESTING).
7 - 14 COOLINGDR
COOLING (Continued)

CONDITION POSSIBLE CAUSES CORRECTION
DETONATION OR PRE-
IGNITION (NOT CAUSED BY
IGNITION SYSTEM). GAUGE
MAY OR MAY NOT BE
READING HIGH1. Engine overheating. 1. Check reason for overheating and
repair as necessary.
2. Freeze point of coolant not
correct. Mixture is too rich or too
lean.2. Check coolant concentration. (Refer to
LUBRICATION & MAINTENANCE/FLUID
TYPES - DESCRIPTION).
HOSE OR HOSES COLLAPSE
WHILE ENGINE IS RUNNING1. Vacuum created in cooling
system on engine cool-down is
not being relieved through
coolant reserve/overflow system.1. (a) Radiator cap relief valve stuck.
(Refer to 7 - COOLING/ENGINE/
RADIATOR PRESSURE CAP -
DIAGNOSIS AND TESTING). Replace if
necessary
(b) Hose between coolant
reserve/overflow tank and
radiator is kinked. Repair as
necessary.
(c) Vent at coolant reserve/
overflow tank is plugged. Clean
vent and repair as necessary.
(d) Reserve/overflow tank is internally
blocked or plugged. Check for blockage
and repair as necessary.
NOISY VISCOUS FAN/DRIVE 1. Fan blades loose. 1. Replace fan blade assembly. (Refer to 7
- COOLING/ENGINE/RADIATOR FAN -
REMOVAL)
2. Fan blades striking a
surrounding object.2. Locate point of fan blade contact and
repair as necessary.
3. Air obstructions at radiator or
air conditioning condenser.3. Remove obstructions and/or clean
debris or insects from radiator or A/C
condenser.
4. Thermal viscous fan drive has
defective bearing.4. Replace fan drive. Bearing is not
serviceable. (Refer to 7 - COOLING/
ENGINE/FAN DRIVE VISCOUS CLUTCH
- REMOVAL).
5. A certain amount of fan noise
may be evident on models
equipped with a thermal viscous
fan drive. Some of this noise is
normal.5. (Refer to 7 - COOLING/ENGINE/FAN
DRIVE VISCOUS CLUTCH -
DESCRIPTION) for an explanation of
normal fan noise.
DRCOOLING 7 - 15
COOLING (Continued)

STANDARD PROCEDURE
STANDARD PROCEDURE - COOLANT LEVEL
CHECK
NOTE: Do not remove radiator cap for routine cool-
ant level inspections. The coolant level can be
checked at coolant recovery bottle or the coolant
degas bottle.
WARNING: DO NOT REMOVE OR LOOSEN THE
RADIATOR CAP WITH THE COOLING SYSTEM HOT
AND UNDER PRESSURE. SERIOUS BURNS FROM
COOLANT OR HIGH PRESSURE STEAM CAN
OCCUR.
The 5.9L, 5.9L Diesel, and 8.0L engine coolant
reserve / overflow system provides a quick method for
determining the coolant level without removing the
radiator pressure cap. With the engine at normal
operating temperature and idling, observe the level
of the coolant on the external level indicator on the
side of the coolant reserve / overflow bottle. The cool-
ant level should be between the MIN and MAX
marks. If the coolant is below the MIN mark, add a
50/50 mixture of antifreeze and water to the bottle
until the level reaches the MIN mark.Do Not Over-
fill the bottle by adding fluid above the MAX
line.This may cause coolant to spill onto the ground
during subsequent vehicle operation.
The 3.7L/4.7L/5.9L engine coolant degas system
provides a quick method for determining the coolant
level with out removing the radiator pressure cap.
With a cold engine, observe the level of coolant in the
degas bottle. The level should be in the COLD FILL
RANGE.DO NOT OVERFILLthe bottle by adding
fluid above the COLD FILL RANGE. This may cause
coolant to spill onto the ground during subsequent
vehicle operation.
STANDARD PROCEDURE - COOLING SYSTEM
CLEANING/REVERSE FLUSHING
CLEANING
Drain the cooling system and refill with water. Run
the engine with the radiator cap installed until the
upper radiator hose is hot. Stop the engine and drain
the water from system. If the water is dirty, fill the
system with water, run the engine and drain the sys-
tem. Repeat this procedure until the water drains
clean.
REVERSE FLUSHING
Reverse flushing of the cooling system is the forc-
ing of water through the cooling system. This is doneusing air pressure in the opposite direction of normal
coolant flow. It is usually only necessary with very
dirty systems with evidence of partial plugging.
REVERSE FLUSHING RADIATOR
Disconnect the radiator hoses from the radiator
inlet and outlet. Attach a section of the radiator hose
to the radiator bottom outlet fitting and insert the
flushing gun. Connect a water supply hose and air
supply hose to the flushing gun.
CAUTION: Internal radiator pressure must not
exceed 138 kPa (20 psi) as damage to radiator may
result.
Allow the radiator to fill with water. When the
radiator is filled, apply air in short blasts. Allow the
radiator to refill between blasts. Continue this
reverse flushing until clean water flows out through
the rear of the radiator cooling tube passages.
REVERSE FLUSHING ENGINE
Drain the cooling system. 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
and attach a lead-away hose to the water pump inlet
fitting.
CAUTION: On vehicles equipped with a heater water
control valve, be sure the heater control valve is
closed (heat off). This will prevent coolant flow with
scale and other deposits from entering the heater
core.
Connect the water supply hose and air supply hose
to 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. Con-
tinue until clean water flows through the lead away
hose.
Remove the lead away hose, flushing gun, water
supply hose and air supply hose. Remove the thermo-
stat housing and install the thermostat. Install the
thermostat housing with a replacement gasket. Refer
to Thermostat Replacement. Connect the radiator
hoses. Refill the cooling system with the correct anti-
freeze/water mixture. Refer to Refilling the Cooling
System.
CHEMICAL CLEANING
In some instances, use a radiator cleaner (Mopart
Radiator Kleen or equivalent) before flushing. This
will soften scale and other deposits and aid flushing
operation.
DRCOOLING 7 - 17
COOLING (Continued)

CAUTION: Follow manufacturers instructions when
using these products.
STANDARD PROCEDUREÐDRAINING COOLING
SYSTEM 3.7L/4.7L/5.7L ENGINE
WARNING: DO NOT REMOVE THE CYLINDER
BLOCK DRAIN PLUGS (Fig. 6) OR LOOSEN THE
RADIATOR DRAINCOCK WITH SYSTEM HOT AND
UNDER PRESSURE. SERIOUS BURNS FROM
COOLANT CAN OCCUR.
(1) With the engine cold, raise the vehicle on a
hoist and locate the radiator draincock.
NOTE: Radiator draincock is located on the left/
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. Remove the
radiator cap, open the draincock and drain the cool-
ing system.
(3) If draining the entire engine is required,
remove the cylinder block drain plugs.
STANDARD PROCEDURE - REFILLING
COOLING SYSTEM 3.7L/4.7L/5.7L ENGINE
DO NOT WASTE REUSABLE COOLANT.Ifthe
solution is clean, drain the coolant into a clean con-
tainer for reuse.(1) Install the cylinder block drain plugs (if
removed). Coat the threads with MopartThread
Sealant with Teflon.
(2) Close the radiator draincock.
CAUTION: Failure to purge air from the cooling sys-
tem can result in an overheating condition and
severe engine damage.
(3) Fill system using a 50/50 mixture antifreeze
and low mineral content water. Stop filling when the
level in the degas bottle has reached the top of the
COLD FILL RANGE.
(4) Start and operate the engine until the thermo-
stat opens (upper radiator hose is warm to the
touch).
(5) If necessary, add a 50/50 mixture of anti-freeze
and water to the degass bottle to maintain the proper
coolant level in the degas bottle.
(6) Install the radiator cap.
STANDARD PROCEDUREÐDRAINING COOLING
SYSTEM 5.9L/8.0L ENGINE
WARNING: DO NOT REMOVE CYLINDER BLOCK
DRAIN PLUGS OR LOOSEN RADIATOR DRAIN-
COCK WITH SYSTEM HOT AND UNDER PRESSURE.
SERIOUS BURNS FROM COOLANT CAN OCCUR.
DO NOT WASTE reusable coolant. If solution is
clean, drain coolant into a clean container for reuse.
(1) Attach one end of a hose to the draincock. Put
the other end into a clean container.
(2)DO NOT REMOVE THE RADIATOR CAP
when draining the coolant from the reservoir/over-
flow tank. Open radiator draincock and when the
tank is empty, remove the radiator cap and continue
draining the cooling system.
(3) If draining the entire engine, remove the cylin-
der block drain plugs. Refer to (Fig. 7).
STANDARD PROCEDUREÐREFILLING
COOLING SYSTEM 5.9L/8.0L ENGINE
WARNING: DO NOT REMOVE CYLINDER BLOCK
DRAIN PLUGS OR LOOSEN RADIATOR DRAIN-
COCK WITH SYSTEM HOT AND UNDER PRESSURE.
SERIOUS BURNS FROM COOLANT CAN OCCUR.
DO NOT WASTE reusable coolant. If solution is
clean, drain coolant into a clean container for reuse.
Clean cooling system prior to refilling. (Refer to 7 -
COOLING - STANDARD PROCEDURE).
(1) Install cylinder block drain plugs. Coat the
threads with MopartThread Sealant with Teflon.
(2) Close radiator petcock.
Fig. 6 Drain Plug - 3.7L/4.7L Engine
1 - CYLINDER BLOCK DRAIN PLUG
2 - EXHAUST MANIFOLD AND HEAT SHIELD
7 - 18 COOLINGDR
COOLING (Continued)

(3) Fill cooling system with a 50/50 mixture of
water and antifreeze.
(4) Fill coolant reserve/overflow tank to MAX mark
on bottle.
(5) Start and operate engine until thermostat
opens (upper radiator hose warm to touch).
(6) If necessary, add a 50/50 water and antifreeze
mixture to the coolant reserve/overflow tank. This is
done to maintain coolant level between the MAX and
MIN marks. The level in the reserve/overflow tank
may drop below the MIN mark after three or four
warm-up and cool-down cycles.
STANDARD PROCEDUREÐDRAINING COOLING
SYSTEM 5.9L DIESEL ENGINE
WARNING: DO NOT REMOVE THE CYLINDER
BLOCK DRAIN PLUGS OR LOOSEN THE RADIATOR
DRAIN PLUG WITH SYSTEM HOT AND UNDER
PRESSURE. SERIOUS BURNS FROM COOLANT
CAN OCCUR.
DO NOT WASTE reusable coolant. If the solution
is clean, drain the coolant into a clean container for
reuse.
(1) Start the engine and place the heater control
temperature selector in the Full-On position.
(2) Turn the ignition off.
(3) Do not remove radiator cap when draining cool-
ant from reserve/overflow tank. Open radiator drain
plug and when tank is empty, remove radiator cap. If
the coolant reserve/overflow tank does not drain,
(Refer to 7 - COOLING - DIAGNOSIS AND TEST-
ING). The coolant need not be removed from tank
unless the system is being refilled with fresh mix-
ture.
(4) Remove radiator pressure cap.
STANDARD PROCEDUREÐREFILLING
COOLING SYSTEM 5.9L DIESEL ENGINE
Clean cooling system prior to refilling (Refer to 7 -
COOLING - STANDARD PROCEDURE).
(1) Close radiator drain plug.
CAUTION: Due to the use of the one-way check
valve, the engine must not be operating when refill-
ing the cooling system.
NOTE: The diesel engine is equipped with two one-
way check valves (jiggle pins). The check valves
are used as a servicing feature and will vent air
when the system is being filled. Water pressure (or
flow) will hold the valves closed.
(2) Fill the cooling system with a 50/50 mixture of
water and antifreeze.
(3) Fill coolant reserve/overflow tank to the FULL
mark.
(4) Start and operate engine until thermostat
opens. Upper radiator hose should be warm to touch.
(5) If necessary, add 50/50 water and antifreeze
mixture to the coolant reserve/overflow tank to main-
tain coolant level. This level should be between the
ADD and FULL marks. The level in the reserve/over-
flow tank may drop below the ADD mark after three
or four warm-up and cool-down cycles.
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
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 a freeze
point of -37ÉC (-35ÉF). If it loses color or becomes con-
taminated, drain, flush, and replace with fresh prop-
erly mixed coolant solution.
CAUTION: Do not use coolant additives that are
claimed to improve engine cooling.
For 5.9L engines, do not remove the radiator cap to
add coolant to the system. When adding coolant to
maintain the correct level, do so only at the reserve/
overflow bottle. Remove the radiator cap only for
testing or when refilling the system after service.
Removing the cap unnecessarily can cause loss of
coolant and allow air to enter the system, which pro-
duces corrosion.
Fig. 7 Cylinder Block Drain Plug - 5.9L Engines
1 - BLOCK DRAIN PLUG
DRCOOLING 7 - 19
COOLING (Continued)

CAUTION: Do not use coolant additives that are
claimed to improve engine cooling.
OPERATION
Coolant flows through the engine block absorbing
the heat from the engine, then flows to the radiator
where the cooling fins in the radiator transfers the
heat from the coolant to the atmosphere. During cold
weather the ethylene-glycol or propylene-glycol cool-
ant prevents water present in the cooling system
from freezing within temperatures indicated by mix-
ture ratio of coolant to water.
COOLANT RECOVERY
CONTAINER-5.9L
DESCRIPTION
The coolant reserve/overflow tank is mounted on
top of the fan shroud, and is made of high tempera-
ture plastic (Fig. 1).
OPERATION
The coolant reserve/overflow system works in con-
junction with the radiator pressure cap. It utilizes
thermal expansion and contraction of coolant to keep
coolant free of trapped air. It provides a volume for
expansion and contraction of coolant. It also providesa convenient and safe method for checking coolant
level and adjusting level at atmospheric pressure.
This is done without removing the radiator pressure
cap. The system also provides some 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.
REMOVAL
(1) Remove recovery hose from radiator.
(2) Remove the coolant container to fan shroud
mounting bolt.
(3) Tilt the container backward towards the engine
to disengage the mounting pin locking features and
lift the container away from the fan shroud (Fig. 1).
INSTALLATION
(1) Align the coolant container mounting pins into
the slots on the fan shroud and push the container
onto the fan shroud.
(2) Secure the container to the fan shroud with the
bolt. Tighten to 8.5N´m (75 in-lbs).
NOTE: Ensure that the locking feature on the
mounting pins has engaged.
(3) Connect the recovery hose to the radiator (Fig.
1).
COOLANT DEGAS
CONTAINER-3.7L/4.7L
DESCRIPTION
The coolant degas container is mounted on top of
the fan shroud and is made of high temperatyre plas-
tic (Fig. 2).
OPERATION
The coolant degas system works in parallel with
the radiator. It is fed through a vent line connected
to the top of the radiator inlet tank and returns to
the engine/coolant pump via the heater return hoses.
This plumbing arrangement, together with the inlet
thermostat, provides for constant flow through the
degas container whenever the engine is running. The
air space in the top of the degas container serves sev-
eral functions. It provides a volume for the expansion
of coolant during engine operation. It provides a
space for quick de-aeration of the coolant. Since the
container is the highest point in the cooling system,
any air trapped in the coolant will quickly be trans-
ported to the degas container and be separated out.
Fig. 1 Coolant Recovery Bottle Ð 5.9L
1 - SCREW
2 - COOLANT RECOVERY CONTAINER
3 - RADIATOR/RADIATOR CAP
4 - FAN SHROUD
7 - 38 ENGINEDR
COOLANT (Continued)

The air space also acts as sort of a spring that pro-
vides constant system pressurization in conjunction
with the radiator cap on top of the container. By
returning coolant to the pump side of the inlet ther-
mostat, the degas container also supplies greater
pressure to the coolant pump, providing for enhanced
coolant flow at high engine speeds.
The degas container also provides a convenient and
safe method for checking the coolant level with out
removing the radiator pressure cap. The degas con-
tainer does not require a separate overflow container
since it was designed with enough volume to provide
a coolant reserve and also protect for any after-boil
conditions.
REMOVAL
(1) Drain enough coolant from the system so that
the degas container is empty. Refer to Draining Cool-
ing System 3.7L/4.7L Engines in this group
(2) Loosen the clamps securing the supply and
return hoses to the container and remove the hoses.
(3) Remove the coolant container to fan shroud
mounting bolts.
(4) Tilt the container back towards the engine to
disengage the mounting pin locking features and lift
the container away from the fan shroud.
INSTALLATION
(1) Align the mounting pins into the slots on the
fan shroud and push the container into the fan
shroud.
(2) Secure the coolant container to the fan shroud
with bolts. Tighten to 8.5 N-m (75 in. lbs).
NOTE: Ensure the locking feature on the mounting
pins has engaged.
(3) Connect the supply and return hoses to the
container and ensure that the hose clamps are posi-
tioned properly.
(4) Refill the cooling system(Refer to 7 - COOLING
- STANDARD PROCEDURE).
RADIATOR FAN
REMOVAL
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.
(1) Disconnect negative battery cable from battery.
(2) Remove coolant reserve/overflow container from
fan shroud and lay aside.Do Notdisconnect the
hoses or drain coolant from the container.
(3) The thermal viscous fan drive/fan blade assem-
bly is attached (threaded) to the water pump hub
shaft (Fig. 4). Remove the fan blade/viscous fan drive
assembly from the water pump by turning the
mounting nut counterclockwise as viewed from the
front. Threads on the viscous fan drive areRIGHT-
HAND.A 36 MM Fan Wrench should be used to pre-
vent pulley from rotating (Fig. 3).
(4)Do Notattempt to remove the fan/viscous fan
drive assembly from the vehicle at this time.
(5)Do Notunbolt the fan blade assembly (Fig. 4)
from viscous fan drive at this time.
(6) Remove the fan shroud-to-radiator mounting
bolts.
(7) Pull the lower shroud mounts out of the radia-
tor tank clips.
(8) Remove the fan shroud and fan blade/viscous
fan drive assembly as a complete unit from vehicle.
(9) After removing the fan blade/viscous fan drive
assembly,do notplace the viscous fan drive in a
horizontal position. If stored horizontally, silicone
Fig. 2 Coolant Degas Container
1 - SCREWS
2 - COOLANT DEGAS CONTAINER
3 - FAN SHROUD
4 - RADIATOR
DRENGINE 7 - 39
COOLANT DEGAS CONTAINER-3.7L/4.7L (Continued)

(6) Install the radiator upper hose to the thermo-
stat housing.
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 wrong direction. Refer to (Fig. 24) for the
correct 5.9L engine belt routing. The correct belt
with correct length must be used.
(7) Air Conditioned vehicles; Install the generator.
Tighten the bolts to 41 N´m (30 ft. lbs.).
(8) Install the support bracket (generator mount-
ing bracket-to-intake manifold). (Fig. 19). Tighten the
bolts to 54 N´m (40 ft. lbs.).
(9) Install the accessory drive belt (Fig. 20)(Refer
to 7 - COOLING/ACCESSORY DRIVE/DRIVE
BELTS - INSTALLATION).
(10) Fill the cooling system (Refer to 7 - COOLING
- STANDARD PROCEDURE).
(11) Connect battery negative cable.
(12) Start and warm the engine. Check for leaks.
ENGINE COOLANT
THERMOSTAT - 3.7L/4.7L
DESCRIPTION
CAUTION: Do not operate the 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. On the 3.7L4.7L engine the
thermostat is designed to block the flow of the cool-
ant bypass journal by 50% instead of completely
blocking the flow. This design controls coolant tem-
perature more accurately (Fig. 25).
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
Fig. 23 Thermostat PositionÐ5.9L EnginesFig. 24 Belt Routing ± 5.9L Engines
1 - IDLER PULLEY
2 - GENERATOR PULLEY
3 - A/C COMPRESSOR PULLEY
4 - IF W/OUT A/C
5 - POWER STEERING PUMP PULLEY
6 - WATER PUMP PULLEY
7 - CRANKSHAFT PULLEY
8 - AUTOMATIC TENSIONER
7 - 50 ENGINEDR
ENGINE COOLANT THERMOSTAT- 5.7L/5.9L (Continued)

This system capacity will not effect warm up or
cold weather operating characteristics if the thermo-
stat is operating properly. This is because coolant
will be held in the engine until it reaches the ther-
mostat ªsetº 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 if the outside temperature is below
4ÉC (40ÉF).Do not use the block heater if the
outside temperature is above 4ÉC (40ÉF).
A ªCold Weather Coverº 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. It attaches to the
front of the vehicle at the grill opening.The cover is
to be used with cool or cold temperatures only.
If used with high outside temperatures, serious
engine damage could result.Refer to the litera-
ture supplied with the cover for additional informa-
tion.
(1) To determine if the thermostat is defective, it
must be removed from the vehicle (Refer to 7 -
COOLING/ENGINE/ENGINE COOLANT THERMO-
STAT - REMOVAL).
(2) After the thermostat has been removed, exam-
ine the thermostat and inside of thermostat housing
for contaminants. If contaminants are found, the
thermostat may already be in a ªstuck openº position.
Flush the cooling system before replacing thermostat
(Refer to 7 - COOLING - STANDARD PROCE-
DURE).
(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) The thermostat will begin to open at 85.5 Ð
89.4ÉC. (186 Ð193ÉF ). If the valve starts to move
before this temperature is reached, it is opening too
early. Replace thermostat. The thermostat should be
fully open (valve will stop moving) at 97ÉC (207ÉF). Ifthe valve is still moving when the water temperature
reaches 97ÉC (207ÉF), it is opening too late. Replace
thermostat. If the valve refuses to move at any time,
replace thermostat.
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 the battery negative cables.
(2) Drain cooling system until coolant level is
below thermostat (Refer to 7 - COOLING - STAN-
DARD 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). SNAP-ON CLAMP TOOL (NUMBER HPC-20)
MAY BE USED FOR LARGER CLAMPS. ALWAYS
WEAR SAFETY GLASSES WHEN SERVICING CON-
STANT 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 a matching number or letter.
(3) Remove radiator hose clamp and hose from
thermostat housing.
(4) Remove the three (3) water outlet-to-cylinder
head bolts and remove the water outlet connector
(Fig. 28).
(5) Clean the mating surfaces of the water outlet
connector and clean the thermostat seat groove at
the top of the thermostat housing (Fig. 28).
INSTALLATION
(1) Inspect thermostat seal for cuts or nicks.
Replace if damaged.
(2) Install the thermostat into the groove in the
top of the cylinder head (Fig. 28).
(3) Install the thermostat housing and bolts.
Tighten the bolts to 10 N´m (88 in. lbs.) torque.
(4) Install the radiator upper hose and clamp.
(5) Fill the cooling system with coolant (Refer to 7
- COOLING - STANDARD PROCEDURE).
(6) Connect the battery negative cables.
DRENGINE 7 - 53
ENGINE COOLANT THERMOSTAT - 5.9L DIESEL (Continued)

occur when ambient (outside air temperature) is very
high.
²Engine loads and temperatures are high such as
when towing a trailer.
²Cool silicone fluid within the fan drive unit is
being redistributed back to its normal disengaged
(warm) position. This can occur during the first 15
seconds to one minute after engine start-up on a cold
engine.
LEAKS
Viscous fan drive operation is not affected by small
oil stains near the drive bearing. If leakage appears
excessive, replace the fan drive unit.
VISCOUS 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. The timing light is to be used as a
strobe light. This step cannot be used on the diesel
engine.
(4) Block the air flow through the radiator. Secure
a sheet of plastic in front of the radiator. 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.
(6) Start the engine and operate at 2400 rpm.
Within ten minutes the air temperature (indicated on
the dial thermometer) should be up to 88É C (190É F).
Fan driveengagementshould start to occur at/be-
tween:
²3.7L Automatic Ð 93É C - 99ÉC (200É F - 210É F)²3.7L Manual/4.7L Automatic/5.9L Ð 85É to 91É C
(185É to 195É F)
²4.7L Manual Ð 74É to 79É C (165É to 175É F)
²Engagement is distinguishable by a definite
increasein fan flow noise (roaring). The timing light
also will indicate an increase in the speed of the fan.
(7) When viscous drive engagement is verified,
remove the plastic sheet. Fan drivedisengagement
should start to occur at or between:
²3.7L Automatic Ð 76ÉC to 81ÉC (168É F to 178É
F)
²3.7L Manual/4.7L Auto/ 5.9L Ð 67ÉC to 73ÉC
(153É F to 163É F)
²4.7L Manual Ð 56ÉC to 62ÉC (133É F to 143É F)
²8.0L engine Ð 88É to 96É C (190É to 205É F) A
definitedecreaseof fan flow noise (roaring) should
be noticed. If not, replace the defective viscous fan
drive unit.
CAUTION: Some 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 overheating.
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.
FAN DRIVE VISCOUS CLUTCH
- 5.9L DIESEL
DESCRIPTION
The electronically controlled thermal viscous fan
drive (Fig. 31) is attached to the fan drive pulley
mounted to the engine. The coupling allows the fan
to be driven in a normal manner. The fan speed is
controlled by the electronic control module.
OPERATION
The Engine Control Module (ECM) controls the
level of engagment of the electronically controlled
viscous fan clutch by monitoring coolant tempera-
ture, intake manifold temperature, and air condition-
ing status. Based on cooling requirements, the ECM
sends a signal to the viscous fan clutch to increase or
decrease the fan speed.
DRENGINE 7 - 55
FAN DRIVE VISCOUS CLUTCH (Continued)