1993 DODGE TRUCK Service Repair Manual

7 - 2
COOLING
SYSTEM

•

NOTE: HEATER
COOLANT FLOW
CIRCUIT
IS
ALWAYS

OPEN
EXCEPT
WHEN
IN MAX. A/C
OR
OFF
MODES
HEATER
INTAKE MANIFOLD
COOLANT FLOW "METERED" FROM REAR
TO

FRONT
AND
BELOW EXHAUST HEAT
CROSSOVER
SHUT
OFF
VALVE

A/C
ONLY COOLANT FLOW
-
PUMP
TO

CYLINDER
BLOCK,
UP
THROUGH
CYLINDER
HEADS
TO
INTAKE MANIFOLD WATER BOX
TO
RADIATOR
—
TO PUMP

•BYPASS
THERMOSTAT CLOSED-HIGH FLOW
THERMOSTAT OPEN
-
LOW FLOW

CYLINDER
HEAD
RR07B52

Fig.
2
Cooling
System
Routing—5.9L (V-8 Gas)—Typical All vehicles are equipped with either a 3.9L (V-6),
a 5.2L (V-8), a 5.9L (LDC-gas V-8), a 5.9L (HDC-gas
V-8) or a 5.9L (in-line 6 cylinder diesel) engine.
As coolant temperature reaches approximately

220°F,
the engine idle speed is increased by the pow-
ertrain control module (PCM) to provide increased
cooling system performance. The PCM was formerly
referred to as the engine controller or SBEC.

COOLING
SYSTEM
COMPONENTS—EXCEPT

DIESEL
ENGINE
The cooling system consists of:
• A down-flow radiator
• Thermal viscous fan drive
• Fan shroud
• Radiator pressure cap
• Thermostat
• Coolant reserve/overflow system
• Transmission oil cooler (automatic transmission)
• Coolant
• Water pump (to circulate coolant)
• Hoses and hose clamps Coolant flow circuits for 3.9L (V-6) and 5.2L (V-8)
engines with water cooled intake manifolds are
shown in figure 1. Coolant flow circuits for 5.9L (V-8 Gas) engines
with water cooled intake manifolds are shown in fig­ ure 2.
COOLING
SYSTEM
COMPONENTS-DIESEL

ENGINE
Coolant flow circuits for 5.9L (diesel) engines with
water cooled intake manifolds are shown in figure 3. The cooling system (Fig. 3) consists of: a cross-flow
radiator, engine driven cooling fan, thermal viscous
fan drive, fan shroud, radiator pressure cap, thermo­ stat, coolant reserve/overflow system, transmission
oil cooler (if equipped with an automatic transmis­
sion),
coolant, water pump, hoses and hose clamps.

SYSTEM
COOLANT ROUTING-DIESEL ENGINE
Coolant is drawn from radiator into the water
pump. Water pump output is directed to the engine oil cooler cavity of the cylinder block (Fig. 4). From the oil cooler cavity, the coolant circulates
around each cylinder. It then crosses to the lift pump
side of engine where it flows up into cylinder head
through openings in top of cylinder block (Fig. 4). Coolant flows past the valve bridges (Fig. 5), to ex­
haust manifold side of engine, to thermostat. As cool­ ant flows toward the thermostat, it provides cooling
for the injector nozzle.
When thermostat is closed (engine is below operating
temperature), coolant flows through bypass passage to
water pump inlet (Fig. 6). Once operating temperature is reached, the thermostat opens and blocks the bypass
passage. Coolant then flows to the radiator inlet.

• COOLING
SYSTEM
7 - 3
Fig. 3 Diesel Engine Cooling System-Typical

1.
Coolant
Flow from Cylinder
Block

2.
Coolant
to Thermostat
Housing

Fig. 4
Cylinder
Block
Coolant
Routing-Diesel Engine Fig 6 coolant Flow at Thermostat-Diesel Engine

DIAGNOSIS

PRELIMINARY
CHECKS

ENGINE COOLING SYSTEM OVERHEATING Establish what driving conditions caused the com­
plaint. Abnormal loads on the cooling system such as
the following may be the cause:

1.
PROLONGED IDLE, VERY HIGH AMBI­
ENT TEMPERATURE, SLIGHT TAIL WIND AT
IDLE, SLOW TRAFFIC, TRAFFIC JAMS, HIGH SPEED OR STEEP GRADES.
Driving techniques that avoid overheating are:
• Idle with A/C off when temperature gauge is at
end of normal range. * Increasing engine speed for more air flow is recom­
mended.

2.
TRAILER TOWING: Consult Trailer Towing section of owners manual.
Do not exceed limits.

3.
AIR CONDITIONING; ADD-ON OR AFTER
MARKET: A maximum cooling package should have been or­
dered with vehicle if add-on or after market A/C is
SYMPTOM AND ACTION

SYMPTOM
installed. If not, maximum cooling system compo­
nents should be installed for model involved per
manufacturer's specifications.

4.
RECENT SERVICE OR ACCIDENT RE­
PAIR:
Determine if any recent service has been performed
on vehicle that may effect cooling system. This may

be:

• Engine adjustments (incorrect timing)
• Slipping engine accessory drive belt(s) • Brakes (possibly dragging)
• Changed parts. Incorrect water pump or pump ro­
tating in wrong direction due to belt not correctly
routed
• Reconditioned radiator or cooling system refilling (possibly under filled or air trapped in system).
If investigation reveals none of the above as a
cause for an engine overheating complaint, refer to
the following Symptom and Action chart:
PRELIMINARY FIRST) ACTION
Blinking Engine Temperature
Warning Light or High Gauge indication - Without Coolant Loss
Normal during temporary operation
with
heavy load, towing
a
trailer,
high
outdoor temperatures, and/or on
a
steep
Loss
grade.

Coolant Loss
Hot Vehicle (Not Engine) Heat Damage,
Hot Carpet, Seat,
Hot
Catalytic
Converter,
Smoke, Burnt Odor
Hot Engine Crackling Noise Hot Smell
Severe Local Hot Spots
Coolant Color
Coolant Reserve Bottle Level Changes
Coolant Not Returning To Radiator
Improper refilling procedures
can
result
in
trapped air
in
the
system.
Subsequent
operation
of the
pressure cap and coolant reserve system
will
deaereate
the

cooling
system.
A low
coolant
level
will
then result
in the
Coolant Reserve
Tank. Add coolant.
If
condition persists,
refer
to
System
Diagnosis.

Check
heat shielding, exhaust
system,
engine emission controls, ignition
timing, engine misfiring.

A
moderate amount
of
sound from heating
metal
can
be
expected
with
any

vehicle. However,
a
crackling sound from
trie
thermostat
housing,
a hot
smell and/or severe local
hot
spots on
an
engine can indicate blocked coolant

passages,
bad castina, core sand deposits and subsequent blockage,
cracked cylinder block
or
head,
or
blown cylinder head gasket. Usually
accompanied
with
coolant
loss.

Coolant
color is
not
necessarily
an
indication
of
adequate
temperature
or

corrosion
protection.
Level changes
are to be
expected as coolant volume fluctuates
with
engine
temperature.
If the
level
in the
bottle
is
between
the
Maximum and Minimum
marks
at
normal engine operating temperature,
the
level
should
return
to

within
that
range
after
operation
at
elevated temperatures.

Coolant
will
not
return
to the
radiator
if the
radiator cap vent valve does
not

function,
if
an
air
leak destroys vacuum,
or if the
overflow
passage
is
blocked
or
restricted. Inspect
all
portions
of the
overflow
passage,
pressure

cap,
filler
neck nipple, hose, and
passages
within
the
bottle
for
vacuum leak
only. Coolant
return
failure
will
be
evident
by a low
level
in the
radiator.
Reserve
bottle
level
should increase during heat-up.

J9207-31

•
COOLING
SYSTEM
7 - 6 COOLING SYSTEM DIAGNOSIS (EXCEPT DIESEL)

CONDITION
AND
CHICK

OPTIONAL
M°¥
GAUGE
READS
LOW
(!) Verify
gauge
reading. Is a low temperature indicated?
(2) Is code 17 recorded in On Board
Diagnostics
memory?
(3) Is the
gauge
reading in the cold
range?

(4) Low coolant level during cold ambient temperatures
(accompanied
with poor heater performance).
(5) Coolant level is correct.

GAUGE
HEADING
HIGH.
NO
PRESSURE
BLOW
OFF
FROM
RADIATOR
PRESSURE
CAP
OR
STEAM
FROM
COOLANT

RESERVE
TANK.

(1) Verify
gauge
reading. Is a high temperature reading indicated?
(2)
Gauge
reading at
"H"
without
signs
of boiling.
(3) Low coolant level in radiator and coolant reserve tank.
(4) Coolant level in radiator is low. But not low in coolant reserve tank.
(5) Test coolant
freeze
point.
(6) Ensure proper coolant flow.
DIAGNOSIS

30° TO 40°

GAUGE
TRAVEL
IS
NORMAL

Normal
Gauge
Travel
(1) Inspect temperature
gauge
sending
unit. Refer to Group 8, Electrical. Repair or replace sending unit as necessary.
(2) If code 17 is recorded, replace the thermostat. If not, the thermostat is not the
cause
of the low
gauge
reading.
(3) Inspect for
disconnected
sending
unit electrical connector or incorrect
sending
unit. Ensure that
gauge
sending
unit is installed

and
not an indicator light switch.
(4)
WARNING:
DO NOT
REMOVE
THE
RADIATOR
CAP
OF A
HOT,
PRESSURIZED
ENGINE.
SERIOUS
INJURY
CAN

RESULT
FROM
SCALDING
COOLANT.

Inspect
coolant level in the coolant reserve tank and radiator.

Inspect
system
for leaks.
(5) Inspect heater door
controls.
Refer to Group 24, Heating and
Air
Conditioning.

TO
TOP
AMBIENT

High
Gauge
Reading
— Hot Weather — Heavy Load
(1) Compare
gauge
reading to
High
Gauge
Reading Illustration
above.

(2) Inspect for grounded
gauge,
sending
unit or circuit. Refer to
Group
8, Electrical.
(3) a — Pill to full.
b
— Inspect for leaks in
system
and repair as
necessary,

c
—
Ensure
radiator pressure cap was shut tight. Verify
proper
operation of the radiator cap upper and lower
seals.

(4) a —
Fill
to full,
b
— Inspect for leaks in the
system
and repair as
necessary,

c
— Inspect for leaks in the coolant reserve tank to radiator
hose.

d
— Verify proper operation of the radiator cap upper and lower
seals.

(5) a — Adjust coolant solution to
50/50
mixture of anti-freeze and water. Refer to Coolant in this
group,

b
— If a reading is not recorded or below
—
50, the mixture is
too
rich. Clean
system
and
fill
with a
50/50
mixture of
anti-freeze and water. Refer to Coolant in this
group.

(6) a •— With the thermostat open and a slight amount of coolant
removed,
inspect for coolant flow through the radiator at
the
filler
neck opening,

b
— Determine reason for lack of coolant flow and repair as
necessary.
J9007-69

7 - 6
COOLING
SYSTEM

• COOLING SYSTEM DIAGNOSIS (EXCEPT DIESEL)—CONTINUED
Condition and Checks
Diagnosis

(7) Other possible
causes.
(7) a — If
symptom
occurs
during high speed operation inspect for

plugged
air
inlet
side of the radiator or condenser,

plugged
radiator core tubes, add on A/C package
without
proper radiator, engine not operating
within
specifications,

dragging
brakes,
trailer
towing or
hill
climbing, or an insect screen.
b — If
symptom
occurs
during high or low
speed
operation inspect for: thermostat being stuck
partially
open if ambient

temperature
is
below
70°F
and
the vehicle
has
high

mileage,
plugged
air
inlet
side of the radiator or
condenser, add on
A/C
with
incorrect radiator.

c
— If
symptom
occurs
during low
speed
operation only, inspect the radiator fan drive. Repair as necessary.

TEMPERATURE
GAUGE
READS
HOT.
PRESSURE
CAP
VENTS
RESULTING
IN
STEAM
AND
COOLANT
TRANSFER
TO

COOLANT
RESERVE
TANK.
(1) Coolant
level
low in radiator and coolant reserve tank. (1) a —
Fill
cooling
system
and vent trapped air.
b — Inspect for leaks. Repair as necessary.

c
—
Ensure
that
pressure cap
is
completely shut and
seals.

d
— If
level
is low in radiator but normal in the coolant reserve tank, check the
filler
cap to coolant reserve
bottle

connection and pressure cap seal.
(2) Test coolant
freeze
point. (2) Adjust coolant to
50/50
mix of
anti-freeze
and
water.
Refer to

Coolant
section in this group.
(3)
Ensure
coolant
is
flowing through system. (3) a — With the coolant
level
low and the thermostat open, check
for coolant flow through the radiator at the
filler
neck.
b — If a
metal
cracking
sound
is heard, inspect for core sand restricting coolant flow through the
water
jacket
and/or a

faulty
cylinder head casting.
(4) Thermostat stuck in the
closed
position
(prevalent
in cold ambient temperatures). (4) Replace thermostat if found to be stuck in
closed
position.
Refer
to the Thermostat Testing section in this group.
(5) Cylinder head gasket leak. (5) Inspect for leaking cylinder head gasket
with
a commercially
available Block Leak Tester.
J9007-57

•

COOLING
SYSTEM
7 - 7 COOLING SYSTEM DIAGNOSIS (EXCEPT DIESELJ-GONTINUED

CONDITION
AND
CHECKS
DIAGNOSIS

TEMPERATURE
GAUGE
IS
INCONSISTENT,
CYCLES
AND/OR
IS
ERRATIC.

(1) Is cycle normal.
MID

(a)
Normal Gauge Reaction to Thermostat Cycle.

MID

(b) Normal Gauge Reaction at Stop After Heavy Use.
(c) Hot Water Build-Up is Normal at
Stop
after
Heavy Use.
(2)
Is
coolant in radiator low (air
will
build up in the cooling
system
(2)
Fill
system,
vent trapped air and check for leaks,
and
cause
the thermostat to open
late).

(3)
Is
a cylinder head gasket leak allowing exhaust
gas
to
enter
(3) a — Test for leaking cylinder head
gasket
leak
with
a
cooling
system
(exhaust
gas
building up in the cooling
system
will
commercially available Block Leak Tester,

cause
the thermostat to open
late).

b
— Check for coolant in engine oil.

c
— Inspect for
white
steam from exhaust
system.

(4)
Water pump impeller loose on shaft.
Loose
accessory
drive belt. (4) Repair or replace as necessary.

(5)
Air leak
on
the
suction
side of the
water
pump (allows air to build (5) Find leak and repair,
up
in cooling
system
causing
thermostat to open
late).

WARNING
LIGHT
GLOWS
ALL
THE
TIME
(VEHICLE
NOT
EQUIPPED
WITH
GAUGE).

(1) Inspect
temperature
gauge
sending
unit. The warning light
sending
(1)
Ensure
that
a warning light
sending
unit
is
installed, unit
has
a screwdriver slot in the electrode (used for calibration).

Gauge
sending
units do not have a slot in the electrode.

NO
GAUGE
READING
INITIALLY
THEN
HOT
INDICATION

(VEHICLE
EQUIPPED
WITH
GAUGE).

(1)
Gauge
stationary
until
very hot, then
moves
immediately to "H"
(1)
Vehicle
is
equipped
with
sending
unit for light not
gauge.
J9007-70

7 - 8
COOLING
SYSTEM

COOLING SYSTEM DIAGNOSIS (EXCEPT DIESEL)—CONTINUED

Condition and Check
Diagnosis

PRESSURE
CAP
VENTS
TO
ATMOSPHERE
AND COOLANT

RESERVE
TANK.
TEMPERATURE
GAUGE
READING
ABOVE

NORMAL
BUT NOT HIGH.
(1) Test radiator pressure cap
relief
pressure. Refer to Radiator Pressure cap section in this group. (1) Replace cap if
relief
pressure is lower than 14 psi.

COOLANT
LOSS
VISIBLE
ON
GROUND
BELOW
VEHICLE,
BUT
NO
PRESSURE
CAP
BLOW
OFF.
(1) Inspect
system
for leaks. (1) Repair as necessary.

COOLANT
LOSS
PAST
PRESSURE
CAP
TOP
SEAL,
VISIBLE
ON
RADIATOR
FILLER
NECK.

(1) With normal gauge reading. (1) a — Pressure cap not installed tightly.
b — Pressure cap top seal leaks.

c
— Pressure cap diaphragm bowed.
d — Damaged radiator
filler
neck.
e — Pressure cap top seal out of position.
(2) With high or low gauge reading on new vehicle. (2) a — Kinked coolant reserve
system
hose.
b — Coolant reserve
system
tank
plastic
tube
plugged,

c
— Pressure cap seal out of position.

DETONATION
OR
PREIGNITION.
NOT
CAUSED
BY IGNITION

OR
ENGINE
CONDITIONS.

(1) Check engine coolant
freeze
point. If the
tester
does
not register a reading or if
the
reading
is
below
50°F,
inspect
ethylene-

glycol/water
ratio.
A 100
percent
solution of ethylene-glycol in
the
system
causes
the engine to run
hotter
and
possibly
overheat. (1) a — Adjust coolant solution to
50/50
water
ethylene-glycol

mixture.

b — If 100
percent
ethylene-glycol solution
is
found in system, clean and flush
system
before
replacing
with
50/50
mixture
of ethylene-glycol and
water.

COOLING
SYSTEM
HOSES
COLLAPSE
ON
COOLDOWN.

(1) Inspect pressure cap
vent
valve. (1) a — Gasket swell can
prevent
valve from opening,
b — Replace pressure cap.
(2) Coolant reserve
tank
hose plugged or kinked. (2) Repair as necessary.
(3) Inside of pressure cap plugged. (3) Clean cap or replace if necessary.

COOLING
SYSTEM
SUSPECTED
AS
CAUSE
OF
INADEQUATE

AIR
CONDITIONING
SYSTEM
PERFORMANCE.

(1) Inspect for plugged radiator and/or condenser. (1) Clean
with
low pressure
water
from fan side.
(2) Inspect for
missing
air
seals
in the recirculating air path. (2) Repair as necessary.

EXCESSIVE
FAN
NOISE

(1) Inspect for loose or
bent
fan blades. (1) Replace fan.
(2) Inspect clearance
between
fan and adjacent
part.
(2) Repair or replace as necessary.
(3) Inspect radiator and condenser for incoming air obstructions. (3) Clean air path
with
low pressure
water
from fan side.
(4) Inspect
viscous
fan drive. (4) Replace if
viscous
drive
does not
operate
properly.

HEAT
ODOR

(1) Was
temperature
gauge reading
high?
(1) If
YES,
refer
to
GAUGE
READING
HIGH. If NO,
refer
to steps
2, 3, and 4.
(2) Are all
heat
shields in place? (2) If
YES,
refer
to
steps
3 and 4. If NO,
repair
as required.
(3) If the air side of the
heat
exchanger
plugged?
(3) Clean as necessary.
(4) Engine running rich
causing
catalytic converter to overheat. (4) Repair as necessary.

POOR
DRIVEABIUTY.
SUSPECT
THERMOSTAT
FAILED
IN
OPEN
POSITION.

(1) Check On-Board
Diagnostics.
Is code 17 set in memory? (1) If
YES,
replace thermostat. If NO,
refer
to the appropriate
Driveability Manual.

J9007-59

•

COOLING
SYSTEM
7 - 9 COOLING SYSTEM DIAGNOSIS (EXCEPT DIESEL)—CONTINUED

Condition
and Chock

Diagnosis

POOR
HEATER
PERFORMANCE.
SUSPECT

THERMOSTAT
FAILED
IN
OPEN
POSITION.

(1)
Does gauge
read
low?
(1) If YES, replace thermostat. If NO, inspect the
auxiliary
heater

vacuum
water valve. The
valve
should
be open except when the
climate
controls are
OFF
or in the
MAX
A/C mode.
(2) Is coolant level
low?
(2)
Fill
cooling system and
inspect for leaks. Repair as
necessary.

(3) Check
On-Board
Diagnostics.
Is
code
17 set in memory? (3) If
YES,
replace thermostat. If NO, inspect the auxiliary heater

vacuum
water valve. The valve
should
be open except when the climate controls are OFF or in the MAX A/C mode.
J9007-61