1953 JEEP DJ engine overheat

TUNE-UP

C-29.
SERVICE
DIAGNOSIS

POOR
FUEL ECONOMY Ignition Timing Slow or Spark Advance Stuck

Carburetor
Float High
Accelerator Pump Not Properly Adjusted High Fuel Pump Pressure

Fuel
Leakage

Leaky
Fuel Pump Diaphragm Loose Engine Mounting Causing High Fuel Level in Carburetor

Low
Compression
Valves Sticking
Spark
Plugs Bad

Spark
Plug Cables Bad
Weak
Coil
or Condenser Improper Valve Tappet Clearance

Carburetor
Air Cleaner Dirty
High Oil Level in Air Cleaner Dragging Brakes

Front
Wheels Out of Alignment

Tires
Improperly Inflated Inaccurate Odometer

Faulty
Fuel Tank Cap
Clogged
Muffler or Bent Exhaust Pipe Sticking Exhaust Manifold Valve

LACK
OF POWER
Low
Compression Ignition System (Timing Late)
Improper Functioning Carburetor
or Fuel Pump

Fuel
Lines
Clogged

Air
Cleaner Restricted Engine Temperature High Improper Tappet Clearance
Sticking Valves
Valve Timing Late

Leaky
Gaskets
Muffler
Clogged

Bent Exhaust Pipe Sticking Exhaust Manifold Valve —
Dauntless V-6 Engine

LOW
COMPRESSION
Leaky
Valves Poor Piston Ring Seal Sticking Valves
Valve Spring Weak or Broken
Cylinder
Scored or Worn
Tappet Clearance Incorrect Piston Clearance too Large

Leaky
Cylinder Head Gasket

BURNED
VALVES AND SEATS Sticking Valves or too Loose in Guides
Improper Timing
Excessive Carbon Around Valve Head and Seat Overheating
Valve Spring Weak or Broken
Valve Tappet Sticking
Valve Tappet Clearance Incorrect
Clogged
Exhaust System

Defective
Valve
Lifter
— Hydraulic
VALVES
STICKING
Warped Valve Improper Tappet Clearance Carbonized or Scored Valve
Stems

Insufficient Clearance Valve Stem to Guide
Weak or Broken Valve Spring Valve Spring Cocked Contaminated Oil

OVERHEATING
Inoperative Cooling System
Theromstat Inoperative Improper Ignition Timing
Improper Valve Timing
Excessive Carbon Accumulation
Fan
Belt too Loose

Clogged
Muffler or Bent Exhaust Pipe
Oil
System Failure Scored or Leaky Piston Rings
Sticking Exhaust Manifold Valve — Dauntless V-6 Engine

POPPING-SPITTING-DETONATION
Improper Ignition Improper Carburetion
Excessive Carbon
Deposit
in
Combustion Chambers
Poor Valve Seating Sticking Valves
Broken Valve Spring Tappets Adjusted too Close
Spark
Plug Electrodes Burned
Water or Dirt in Fuel
Clogged
Lines Improper Valve Timing

Clogged
Fuel Filter Sticking Exhaust Manifold Valve —
Dauntless V-6 Engine

EXCESSIVE
OIL CONSUMPTION Piston Rings Stuck in Grooves, Worn or Broken Piston Rings Improperly Fitted or Weak Piston Ring Oil Return
Holes
Clogged

Excessive Clearance, Main and
Connecting Rod Bearings

Oil
Leaks at Gaskets or Oil Seals
Excessive Clearance, Valve Stem
to Valve Guide (Intake)

Cylinder
Bores Scored, Out-of-
Round or Tapered
Too Much Clearance, Piston to Cylinder Bore
Misaligned Connecting Rods
High Road
Speeds
or Temperature
Crankcase
Ventilator Not Operating

BEARING
FAILURE
Crankshaft
Bearing Journal Out-of-Round

Crankshaft
Bearing Journal Rough

Lack
of Oil
Oil
Leakage

Dirty
Oil

Low
Oil Pressure or Oil Pump Failure

Drilled
Passages
in Crankcase or Crankshaft
Clogged

Oil
Screen Dirty
Connecting Rod Bent 34

D

HURRICANE
F4
ENGINE
D-112.
SERVICE
DIAGNOSIS

Poor
Fuel
Economy Ignition Timing Slow or Spark Advance Stuck

Carburetor
Float High
Accelerator Pump Not Properly Adjusted
High
Fuel
Pump Pressure

Fuel
Leakage
Leaky
Fuel
Pump Diaphragm
Loose Engine Mounting Causing High
Fuel
Level

in
Carburetor

Low
Compression Valves Sticking

Spark
Plugs Bad

Spark
Plug Cables Bad Weak
Coil
or Condenser Improper Valve Tappet Clearance

Carburetor
Air Cleaner Dirty
High Oil Level in Air Cleaner Dragging Brakes

Front
Wheels Out of Alignment
Tires
Improperly Inflated Inaccurate Odometer

Faulty
Fuel
Tank
Cap

Clogged
Muffler or Bent Exhaust Pipe

Lack
of Power
Low
Compression Ignition System (Timing Late)
Improper Functioning Carburetor or
Fuel
Pump

Fuel
Lines
Clogged
Air
Cleaner Restricted
Engine Temperature High Improper Tappet Clearance
Sticking Valves Valve Timing Late

Leaky
Gaskets
Muffler
Clogged
Bent Exhaust Pipe

Defective
Spark Plugs—Clean or Replace
Defective
Breaker Points—Replace
Points

Incorrect Breaker Point Gap—Reset
Points

Defective
Condenser or Coil—Replace
Loose Electrical Connections—Locate and Tighten
Broken Valve Spring—Replace Spring Broken Piston or Rings—Replace
Defective
Head Gasket—Replace Gasket
Cracked
Distributor Cap—Replace Cap

Low
Compression
Leaky
Valves
Poor Piston Ring Seal Sticking Valves
Valve Spring Weak or Broken
Cylinder
Scored or Worn
Tappet Clearance Incorrect
Piston Clearance too Large
Leaky
Cylinder Head Gasket
Burned Valves and
Seats
Sticking Valves or too Loose in Guides Improper Timing
Excessive Carbon Around Valve Head and Seat Overheating
Valve Spring Weak or Broken Burned Valves and Seats—Continued
Valve Tappet Sticking
Valve Tappet Clearance Incorrect
Clogged
Exhaust System
Valves Sticking Warped Valve Improper Tappet Clearance
Carbonized or Scored Valve
Stems
Insufficient Clearance Valve Stem to Guide
Weak or Broken Valve Spring Valve Spring Cocked Contaminated Oil
Overheating Inoperative Cooling System
Thermostat Inoperative Improper Ignition Timing
Improper Valve Timing
Excessive Carbon Accumulation

Fan
Belt too Loose

Clogged
Muffler or Bent Exhaust Pipe

Oil
System Failure
Scored or Leaky Piston Rings

Popping-Spitting-Detonation
Improper Ignition
Improper Carburetion
Excessive Carbon
Deposit
in Combustion
Cham­
bers
Poor Valve Seating Sticking Valves
Broken Valve Spring Tappets Adjusted too Close

Spark
Plug Electrodes Burned
Water or Dirt in
Fuel
Clogged
Lines Improper Valve Timing
Excessive Oil Comsumption Piston Rings Stuck in Grooves, Worn or Broken Piston Rings Improperly Fitted or Weak Piston Ring Oil Return
Holes
Clogged
Excessive Clearance, Main and Connecting Rod
Bearings

Oil
Leaks at Gaskets or Oil Seals
Excessive Clearance, Valve Stem to Valve Guide (Intake)

Cylinder
Bores Scored, Out-of-Round or Tapered Too Much Clearance, Piston to Cylinder Bore
Misaligned Connecting Rods
High Road
Speeds
or Temperature
Crankcase
Ventilator Not Operating
Bearing Failure
Crankshaft
Bearing Journal Out-of-Round

Crankshaft
Bearing Journal Rough

Lack
of Oil
Oil
Leakage
Dirty
Oil

Low
Oil Pressure or Oil Pump Failure
Drilled
Passages
in Crankcase or Crankshaft
Clogged

Oil
Screen Dirty Connecting Rod Bent 70

'Jeep'
UNIVERSAL
SERIES SERVICE
MANUAL

Dl
Dl-104.
SERVICE
DIAGNOSIS

Poor Fuel Economy
Ignition Timing Late or Spark Advance Inoperative

Carburetor
Float Setting Too High
Accelerator Pump Improperly Adjusted
Fuel
Pump Pressure High

Fuel
Line
Leakage

Fuel
Pump Diaphragm Leakage
Cylinder
Compression Low
Valves Do Not Seat Properly
Spark
Plugs
Defective

Spark
Plug Cables
Defective

Ignition
Coil
or Capacitor
Defective

Carburetor
Air Cleaner Dirty

Brakes
Drag
Wheel Alignment Incorrect

Tire
Pressure Incorrect Odometer Inaccurate

Fuel
Tank
Cap Clogged or
Defective

Muffler or Exhaust Pipe Clogged or Bent

Lack
of
Power
Cylinder
Compression Low
Ingitdon Timing Late

Carburetor
or
Fuel
Pump Clogged or
Defective

Fuel
Lines Clogged
Air
Cleaner Restricted
Engine Temperature High Valves Do Not Seat Property

Valve
Timing Late Intake Manifold or Cylinder Head
Gasket Leaks
Muffler or Exhaust Pipe Clogged or Bent
Spark
Plugs Dirty or
Defective

Breaker
Point Gap Incorrect
Breaker
Points
Defective
Ignition
Coil
or Capacitor
Defective

Electrical
Connection Loose
Broken
Valve Spring

Broken
Piston Ring or Piston
Cylinder
Head Gasket
Defective

Distributor Cap Cracked

Low
Compression
Valves Not Seating Properly Piston Rings Seal Poorly
Valve
Spring Weak or Broken
Cylinder
Scored or Worn
Piston Clearance Too Great

Cylinder
Head Gasket Leaks

Burned
Valves and
Seats
Valves Stick or Are Too Loose in Guides
Valve
Timing Incorrect

Valve
Head and Seat Have Excessive Carbon
Engine Overheats

Valve
Spring Weak or Broken

Valve
Lifter Seized or Collapsed
Exhaust
System Clogged
Valves Sticking

Valve
Stem Warped

Valve
Stem Carbonized or Scored

Valve
Stem Clearance Insufficient in Guide

Valve
Spring Weak or Broken

Valve
Spring Distorted
Oil
Contaminated

Overheating
Cooling System Inoperative
Thermostat Inoperative Ignition Timing Incorrect

Valve
Timing Incorrect
Carbon
Accumulation Excessive

Fan
Belt Loose
Muffler or Exhaust Pipe Clogged or Bent

Oil
System Failure
Piston Rings Worn or Scored
Popping,
Spitting,
Detonation
Ignition Timing Incorrect

Carburetion
Improper

Carbon
Deposit
in Combustion
Chambers Excessive
Valves Not Seating Properly
Valve
Spring Broken
Spark
Plug Electrodes Burned
Water or Dirt in
Fuel
Fuel
Line
Clogged
Valve
Timing Incorrect

Excessive
Oil
Consumption
Piston Rings Stuck in Grooves, Weak,
Worn,
Broken, or Incorrectly Fitted

Crankshaft
Main Bearings or
Connecting Rod Bearings Have
Excessive Clearance
Gaskets or Oil Seals
Leak

Cylinder
Bores Worn, Scored,
Out-of-Round or Tapered
Pistons Have Too Great Clearance to Cylinder Bores
Connecting Rods Misaligned High Road Speed
High Temperature

Crankcase
Ventilation System Inoperative
Bearing Failure
Crankshaft
Bearing Journal Rough or Out-of-Round

Oil
Level Low
Oil
Leakage

Oil
Dirty
Oil
Pressure Low or Lacking
(Oil
Pump Failure)

Drilled
Passages
in Crankshaft or
Crankcase
Clogged

Oil
Screen Dirty
Connecting Rod Bent 105

'Jeep*
UNIVERSAL
SERIES
SERVICE
MANUAL

COOLING
SYSTEM

Contents

SUBJECT
PAR.

GENERAL
.G-l Antifreeze Solutions. .G-l6
Cylinder
Block.
..................
.G-8

Draining
Cooling System............... G-3

Engine
Overheating..
.................
.G-19
Fan
Belt.
......... .........
.G-18
Filling
Cooling System.................
G-2

Inhibited
Coolant Solution .G-l7

Temperature
Sending Unit.
...........
.G-l0

Thermostat
.........................
G-9

RADIATOR
.G-5
Radiator
and Heater Hoses.............
G-7
SUBJECT
PAR.

Radiator
Pressure
Cap.................
G-4

Radiator
Removal and Replacement..... G-6

WATER
PUMP.
. . .G-ll
Water
Pump Disassembly. .............G-13

Water
Pump Inspection.
..............
.G-12

Water
Pump Reassembly.
.............
.G-14

Water
Pump Removal and Replacement. .G-l5

SERVICE
DIAGNOSIS.
.G-20

SPECIFICATIONS
. .G-21

ANTIFREEZE
CHART.
..... ... .G-22

G-l. GENERAL
a.
The satisfactory performance of the Hurricane

F4
engine
is controlled to a great
extent
by the proper operation of the cooling system. The
engine

block is full length water jacketed which prevents
distortion of the cylinder walls. Directed cooling
and
large water holes, properly placed in the cylin­
der head gasket cause more water to flow past the
valve
seats
(which are the
hottest
parts of the

block)
and
carry
the heat away from the valves, giving positive cooling of valves and seats.

Minimum
temperature of the coolant is controlled by a thermostat mounted in the
outlet
passage of
the engine. When the coolant temperature is below
thermostat-rated temperature, the thermostat re­ mains closed and the coolant is directed through
the radiator-bypass
hose
to the water pump. When the thermostat opens, coolant flow is directed to
the top of the radiator. The radiator dissipates the
excess
engine
heat before the coolant is recirculated
through the engine.
The
cooling system is pressurized. Operating pres­
sure
is regulated by the rating of the radiator cap

which
contains a relief valve, b. The Dauntless V-6
engine
efficiency and per­formance is controlled to a great
extent
by proper
operation of the cooling system. The cooling system

does
more than cool the engine. It also directs
the flow of coolant to provide the
best
operating
temperature range for each part of the engine.

In
the Dauntless V-6
engine
coolant is forced by
the water pump into two main passages that run the length of the block on each side (Fig. G-l).
FIG.
G-1—COOLANT
FLOW
THROUGH
THE
DAUNTLESS
V-6
ENGINE

161

COOLING
SYSTEM

14263

FIG.
G-2—COOLING SYSTEM
COMPONENTS
V-6
ENGINE

1—
Radiator
Pressure Cap

2—
Hose
Clamp

3—
Radiator
Hose (Inlet-Upper)
4—
Radiator
Hose (Outlet-Lower) 5—
Bolt
6—
Water
Pump Assembly 7—
Cap
8—Thermostat
By-Pass Hose
g—Water Outlet
Elbow

10—
Gasket

11—
Thermostat
12—
Water
Pump Gasket

13—
Dowel
Pin
14—
Radiator
Shroud (Heavy Duty Cooling) 15—
Pulley

16—
Fan
Spacer
17—
Fan
and Alternator Belt

18—Fan

19—
Lockwasher

20—
Radiator

21—
Drain
Cock
From
these
main passages, the coolant flows around
the
full
length of each combustion chamber.

After
cooling the block, the coolant passes through
ports between the block and each cylinder head.
These
ports direct most of the coolant flow around the exhaust valve area to prevent hot exhaust
gases

from
overheating the exhaust ports.

From
the cylinder heads, the water passes into a
water
manifold between each of the heads and the

water
pump. If the thermostat is closed, the coolant
is ported back to the pump where it is recirculated

back
into the pump and into the engine. After the
coolant heats enough to open the thermostat, the coolant is directed from the water manifold through
a
hose
to the top of the radiator and then through
the radiator which acts as a heat exchanger to cool the fluid. The coolant is then ported through a
hose

from
the bottom of the radiator to the pump, which

recirculates
it back to the engine.

The
cooling system is pressurized. Operating pres­
sure
is regulated by a relief valve in the radiator

cap. The
heater inlet
hose
is connected to a port on
the right bank cylinder head. The outlet
hose
is connected to the heater adapter tube on the water

pump.

c.
It is recommended when using water for coolant
that the cooling system be flushed and checked for leaks twice a year, preferably in the
fall
before
antifreeze is added and in the spring when the antifreeze is drained.

Reverse
flushing
will
aid greatly in removing rust 162

G
COOLING SYSTEM
engine
connections. Insert flushing gun and flush
heater core.
Care
must be taken when applying air
pressure to prevent damage to the heater core.

G-2.
Filling
Cooling System
To
fill
the cooling system, remove the
fill
cap and

fill
the tank to the top. Replace the cap and run
the
engine
at medium speed for approximately one
minute. Remove the cap and recheck the coolant level. Add more coolant if necessary to bring the level back to the top of the tank. If the cooling system is filled when the
engine
is cold, recheck the coolant level after the
engine
has warmed up.
This

will
ensure that the thermostat has opened allow­ ing complete cooling system circulation.

Always
correct any cooling system leaks before installing antifreeze. A corrosion inhibitor should be used in the cooling system to prevent the forma­
tion of rust and scale. A quality brand antifreeze containing a corrosion inhibitor should be used.

When
the antifreeze is drained in the spring, a
corrosion inhibitor should be added with the water.

Note:
Cooling system components for both V6 and

F4
engines
are shown in
Figs.
G-2 and G-3.

G-3. Draining
Cooling System

To
completely
drain
the cooling system, open the

drain
in the
bottom
of the radiator and also a

drain
on the right side of the cylinder block on the
Hurricane
F4 engine. The Dauntless V-6
engine

has two
drain
plugs, one located on each side of the cylinder block. Both plugs must be removed to
completely
drain
the cooling system.
Remove the radiator cap to break any vacuum
that may have developed.

Should
the cooling solution be lost from the system

and
the
engine
become
overheated do not
refill

the system immediately but allow the
engine
to cool or
refill
slowly while the
engine
is running. If
cold solution is poured into the radiator while the

engine
is overheated there is danger of cracking the

cylinder
block and/or cylinder head.
G-4.
Radiator Pressure
Cap

All
radiators are equipped with pressure caps which
reduce evaporation of cooling solution and make the
engines
more efficient by permitting slightly
higher operating temperatures. When operating
properly,
the pressure cap permits pressure build-up

in
the cooling system during periods of severe heat

load.
This
pressure increases the boiling point of the coolant and thus reduces overflow losses. The

effectiveness
of the cap is limited by its opening
pressure and the boiling point of the coolant (see
note
below). The pressure cap employs a spring-
loaded, rubber-faced pressure seal which presses against a seat in the radiator top tank. Spring pres­

sure
determines the opening pressure of the valve.

A
typical pressure cap is shown in Fig. G-5.

Note:
Refer to cooling system specifications (Par.

G-21)
for opening (relief) pressure when the ve­
hicle is equipped with either the
Hurricane
F4
or
Dauntless V-6 engine. If a new cap is required, always install a cap of the same type and pressure
rating
specified. It should never be altered or re­
placed by a plain cap.

A
vacuum release valve (Fig. G-5) is employed to
prevent undesirable vacuum build-up when the system
cools
down. The vacuum release valve is
held against its seat under light spring pressure.

Vacuum
in the system is relieved by the valve
which
opens
at V2 to 1 psi. [0,035 a 0,07 kg-cm2]

vacuum.
A pressure tester can be used to check and
test
the vacuum pressure rate (see Fig. G-6).
Although the mechanism of the pressure cap re­ quires no maintenance, the cap should be inspected
periodically for cleanliness and freedom of opera­ tion. The pressure cap gasket and radiator filler neck seat should also be inspected to be sure they

are
providing a proper seal. If the rubber face of
the valve is defective, a new cap should be installed.
Filler
neck reseating
tools
are commercially
avail­
able to correct minor
defects
at the surface of the seat. Follow instructions of the reseating tool manu­

facturer.

To
remove the radiator pressure cap when the
engine
coolant temperature is high or boiling, place

a
cloth over the pressure cap and
turn
counter­ clockwise about Vi
turn
until the first (pressure release)
stop
is reached. Keep the cap in this posi­
tion until all pressure is released.
Then
push cap
down and
turn
still
further until cap can be re­ moved. To install the pressure cap, place it in posi­
tion and
turn
it clockwise as far as it
will
go.

Caution:
Use extreme care in removing the radiator
pressure cap. In overheated systems, the sudden release of pressure can cause a steam flash and this

flash,
or the
loosened
cap can cause serious personal

injury.

G-5.
RADIATOR

Maintenance of the radiator consists of keeping
the exterior of the radiator core clean, the interior free from rust and scale, and the radiator free from

leaks.
Check
the cooling system fluid level and for
leaks each
2000
miles
[3.200
km.] or every 30
days, whichever occurs first.
This
exterior of the

radiator
core should be cleaned and the radiator inspected for leaks each
6000
miles
[9.600
km.]
of normal service of the vehicle. Cleaning should be performed by blowing out with air stream or water stream directed from the
rear
of the radiator.

Visual
inspection is not sufficient as the accumula­ tion of small particles of foreign material on core
surfaces can restrict cooling without closing the core openings.

Radiator
leakage occasionally results from cor­
rosion perforation of the metal but most leakage results from mechanical failure of soldered joints
when too much strain has been put on the joint.
Fractures
occur most
often
at the joint where the
radiator
inlet and
outlet
pipes are attached to the

tanks.
When the seams break, the entire soldered

joint
is
exposed
and can corrode, but breakage
rather
than corrosion is the
primary
cause of seam
leakage. Examine the radiator carefully for leaks before and after cleaning. Cleaning may uncover points of leakage already existing but plugged with
rust.
White, rusty, or colored leakage stains indicate 164

G
COOLING SYSTEM and
the outlet
hose
is connected to the water pump
housing.
When
installing a new hose, clean the pipe connec­
tions and apply a thin layer of nonhardening seal­
ing compound. Hose clamps should be properly
located over the connections to provide secure fastening. The pressurized cooling system pressure

can
blow off improperly installed hoses.

G-8.
Cylinder
Block

Any
coolant leaks at the engine block water joints

are
aggravated by pump pressure in the water

jacket
and by pressure developed in the cooling system when the pressure cap is in place.
Small
leaks showing up only as moist
spots
often
cannot
be detected when the engine is hot except by the
appearance of rust, corrosion, and dye stains where
leakage evaporated. Also, expansion and contrac­ tion of the engine block resulting from extreme
temperature changes can aggravate leaks. For
these

reasons, when checking for coolant leaks inspect
the block when it is cold and while the engine is

running.
A
leaking
drain
cock or plug that cannot be stopped

leaking
by tightening should be replaced.
Leaking

core-hole expansion plugs should be replaced.
If
tightening gasketed joints
will
not correct leak­
age, install new gaskets. Use a sealing compound
where recommended.

G-9.
Thermostat
a.
The cooling system of the engine is designed
to provide adequate cooling under most adverse conditions. However, it is necessary to employ
some

device to provide quick warming and to prevent
overcooling during normal operation. Automatic
control
of engine operating temperature is provided
by a water flow control thermostat installed in the
water
outlet of the
Hurricane
F4 engine. The ther­
mostat is a heat-operated valve. It should always
be maintained in working order and the vehicle
should never be driven without one installed as there would then be no control of engine tempera­

ture.
The temperature at which the thermostat
opens
is preset and cannot be altered.

b.
The thermostat on the
Hurricane
F4 engine is
located in a housing on the top front of the cylinder

head.
On the Dauntless V-6 engine it is located
in
the thermostat housing of the air intake manifold.

The
standard engine thermostat for the
Hurricane

F4
and Dauntless V-6 engine has a normal rating
of
190°F.
[87.8°C]
and should begin to open at

a
coolant temperature between
180°F.
[82°C]
to
192°F.
[89°C]
and be fully open at
202°F.
[94°C.].
See Fig. G-7 for method of testing.

When
the thermostat is not operating properly, the engine may
run
too hot or too cold. Overheating

may
damage the thermostat so that its valve
will

not function properly, and a cold engine
will
not achieve
full
efficiency.
Rust
can also interfere with
thermostat operation. To
test
the thermostat, place

it
in water heated approximately
25°F.
[17°C]
above the temperature stamped on the thermostat

valve.
Submerge the bellows completely and agitate
the water thoroughly. The valve should open fully.
Next, place the thermostat in water heated approxi-
FIG.
G-7—THERMOSTAT
TEST

mately 10°F.
[11°C]
below the temperature
stamped on the thermostat valve. Submerge the bellows completely and agitate the water thorough­
ly.
The valve should close completely. If the ther­
mostat fails either of
these
tests, it should be re­ placed with a new one of the same type and rating.

G-10. Temperature
Sending Unit

The
sending unit incorporates a temperature sens­ ing element that when it is surrounded by cold engine coolant, the unit provides the highest resist­
ance in the temperature
gauge
indicator
circuit.
Resultant
low current flow in the circuit causes the

indicator
on the instrument panel to read at the low (C) end of the
gauge.
As engine coolant tem­

perature
increases, the resistance of the unit is
decreased allowing an increased current flow in
the
circuit,
making the instrument panel
gauge

register in proportion to the temperature of the engine coolant.

To
test
the sending unit, first run the engine until

it
has had time enough to warm up.
If
no reading is indicated on the
gauge,
check the
sending unit to
gauge
wire by removing the wire

from
the sending unit and momentarily grounding
the wire. If the
gauge
now indicates, the sending

unit
is faulty. If the
gauge
still
does
not indicate, the wire is defective.
Repair
or replace the wire,

a.
Hurricane
F4 Engine.

The
thermo-couple coolant temperature sending
unit
is mounted in the right
rear
of the cylinder head (Fig. G-8) and is connected by a single wire
to the dash unit of the instrument cluster. 166

'Jeep'
UNIVERSAL
SERIES SERVICE
MANUAL

G
cation period. It is
good
preventive maintenance to
replace a badly frayed, worn or cracked fan belt
before it breaks in operation.

To
replace the fan belt,
loosen
the attaching
bolts

at each generator or alternator brace-to-engine mounting and pivot the alternator or generator to­

ward
the
engine
to gain slack needed to install the new belt Remove the old belt. Position the new
belt over the fan pulley, over the crankshaft pulley,
then over the generator or alternator pulley.
Pull
the generator or alternator away from the
engine

until
belt tension is
firm.
Then tighten the generator

or
alternator mounting
bolts
and check the tension
as indicated above. Reset the generator or alternator as necessary for correct belt tension.
Finally,
torque
the generator or alternator mounting
bolts
25 to 35 lb-ft. [3,4 a 4,8 kg-m.].

Note:
On the Dauntless V-6
engine
when adjusting
the fan belt tension, the alternator mounting
bolts

should be torqued 30 to 40 lb-ft. [4,14 to 5,53

kg-m.].
If a fan belt tension
gauge
(W-283) is
avail­

able, proper tension should be 80 pounds [36,2 kg.].

G-l
9. Engine Overheating

An
engine
will
not be damaged by high coolant
temperatures unless the coolant boils. The pres­

surized
cooling system on the 'Jeep' vehicles raises the boiling point of the coolant solution. Should
overheating be encountered, and the fault is be­
lieved to be in the cooling system check for the
following:

a.
Proper coolant level. See
Filling
Cooling Sys­
tem Par. G-2.
b. Poor air flow.
Check
for dirty radiator core. (See Radiator Par. G-5).
Check
for faulty belt
pulley operation, worn or
loose
fan belt, or dam­ aged fan.
Clean,
repair, replace or adjust as neces­

sary.

c. Foaming coolant.
Check
for air leaks at water
pump,
hose
connection and filler cap. Tighten, re­

pair
or replace as necessary.

d.
Surging or "after boil".
Check
pressure cap and
replace if valves or gasket are faulty.
e.
External
leaks.
Check
the following for leaks:
Hoses and clamps, water pump, radiator, head gas­
ket, core plugs and drain cocks, as well as the cylin­ der head or block for
cracks.

f.
Internal
leaks.
Check
for faulty head gasket,
cracked
cylinder head or block.
g. Poor coolant flow.
Check
hose
condition, water pump, fan belt, and repair or replace as necessary. Inspect block for rust or scale, and clean and flush
the system, if necessary.

h.
Check
the temperature
gauge.
169