2002 DODGE RAM heater

ENGINE COOLANT TEMP
SENSOR - 5.9L
DESCRIPTION
The Engine Coolant Temperature (ECT) sensor is
used to sense engine coolant temperature. The sensor
protrudes into an engine water jacket.
The ECT sensor is a two-wire Negative Thermal
Coefficient (NTC) sensor. Meaning, as engine coolant
temperature increases, resistance (voltage) in the
sensor decreases. As temperature decreases, resis-
tance (voltage) in the sensor increases.
OPERATION
At key-on, the Powertrain Control Module (PCM)
sends out a regulated 5 volt signal to the ECT sensor.
The PCM then monitors the signal as it passes
through the ECT sensor to the sensor ground (sensor
return).
When the engine is cold, the PCM will operate in
Open Loop cycle. It will demand slightly richer air-
fuel mixtures and higher idle speeds. This is done
until normal operating temperatures are reached.
The PCM uses inputs from the ECT sensor for the
following calculations:
²for engine coolant temperature gauge operation
through CCD or PCI (J1850) communications
²Injector pulse-width
²Spark-advance curves
²ASD relay shut-down times
²Idle Air Control (IAC) motor key-on steps
²Pulse-width prime-shot during cranking
²O2 sensor closed loop times
²Purge solenoid on/off times
²EGR solenoid on/off times (if equipped)
²Leak Detection Pump operation (if equipped)
²Radiator fan relay on/off times (if equipped)²Target idle speed
REMOVAL
WARNING: HOT, PRESSURIZED COOLANT CAN
CAUSE INJURY BY SCALDING. COOLING SYSTEM
MUST BE PARTIALLY DRAINED BEFORE REMOV-
ING THE COOLANT TEMPERATURE SENSOR.
REFER TO GROUP 7, COOLING.
(1) Partially drain cooling system (Refer to 7 -
COOLING - STANDARD PROCEDURE).
(2) Remove air cleaner assembly.
(3) Disconnect electrical connector from sensor
(Fig. 14).
(4)Engines with air conditioning:When
removing the connector from sensor, do not pull
directly on wiring harness. Fabricate an L-shaped
hook tool from a coat hanger (approximately eight
inches long). Place the hook part of tool under the
connector for removal. The connector is snapped onto
the sensor. It is not equipped with a lock type tab.
(5) Remove sensor from intake manifold.
INSTALLATION
(1) Install sensor.
(2) Tighten to 6±8 N´m (55±75 in. lbs.) torque.
(3) Connect electrical connector to sensor. The sen-
sor connector is symmetrical (not indexed). It can be
installed to the sensor in either direction.
(4) Install air cleaner assembly.
(5) Refill cooling system (Refer to 7 - COOLING -
STANDARD PROCEDURE).
Fig. 13 Block HeaterÐDiesel Engine
1 - BLOCK HEATER
Fig. 14 Engine Coolant Temperature
1 - GENERATOR
2 - A/C COMPRESSOR
3 - ENGINE COOLANT TEMPERATURE SENSOR
4 - ELEC. CONN.
BR/BEENGINE 7 - 47
ENGINE BLOCK HEATER - 5.9L DIESEL (Continued)

ENGINE COOLANT
THERMOSTAT - 5.9L
DESCRIPTION
CAUTION: Do not operate an engine without a ther-
mostat, except for servicing or testing.
The thermostat on the 5.9L gas powered engine is
located beneath the thermostat housing at the front
of the intake manifold (Fig. 15).
The thermostat is a wax pellet driven, reverse pop-
pet choke type.
Coolant leakage into the pellet container will cause
the thermostat to fail in the open position. Thermo-
stats very rarely stick. Do not attempt to free a ther-
mostat with a prying device.
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 longer engine
warmup time, unreliable warmup performance,
increased exhaust emissions and crankcase condensa-
tion that can result in sludge formation.
OPERATION
The wax pellet is located in a sealed container at
the spring end of the thermostat. When heated, thepellet expands, overcoming closing spring tension
and water pump pressure to force the valve to open.
DIAGNOSIS AND TESTINGÐTHERMOSTAT
ON-BOARD DIAGNOSTICS
Allgasoline powered modelsare equipped with
On-Board Diagnostics for certain cooling system com-
ponents. Refer to On-Board Diagnostics (OBD) in the
Diagnosis section of this group for additional infor-
mation. If the powertrain control module (PCM)
detects low engine coolant temperature, it will record
a Diagnostic Trouble Code (DTC) in the PCM mem-
ory. Do not change a thermostat for lack of heat as
indicated by the instrument panel gauge or by poor
heater performance unless a DTC is present. Refer to
the Diagnosis section of this group for other probable
causes. For other DTC numbers, (Refer to 25 - EMIS-
SIONS CONTROL - DESCRIPTION).
The DTC can also be accessed through the DRB
scan tool. Refer to the appropriate Powertrain Diag-
nostic Procedures information for diagnostic informa-
tion and operation of the DRB scan tool.
REMOVAL
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.
Factory installed thermostat housings on 3.9L,
5.2L and 5.9L engines are installed on a gasket with
an anti-stick coating. This will aid in gasket removal
and clean-up.
(1) Disconnect negative battery cable at battery.
(2) Drain cooling system until coolant level is
below thermostat (Refer to 7 - COOLING - STAN-
DARD PROCEDURE).
(3) Air Conditioned vehicles: Remove support
bracket (generator mounting bracket-to-intake mani-
fold) located near rear of generator (Fig. 16).
NOTE: On air conditioning equipped vehicles, the
generator must be partially removed.
(4) Remove accessory drive belt (Refer to 7 -
COOLING/ACCESSORY DRIVE/DRIVE BELTS -
REMOVAL) (Fig. 17).
(5) Remove two generator mounting bolts. Do not
remove any wiring at generator. If equipped with
4WD, unplug 4WD indicator lamp wiring harness
(located near rear of generator).
Fig. 15 Thermostat - 5.9L Gas Powered Engines
1 - THERMOSTAT HOUSING
2 - GASKET
3 - INTAKE MANIFOLD
4 - THERMOSTAT
5 - MACHINED GROOVE
7 - 48 ENGINEBR/BE

ENGINE COOLANT
THERMOSTAT - 8.0L
DESCRIPTION
CAUTION: Do not operate an engine without a ther-
mostat, except for servicing or testing.
The thermostat on all gas powered engines is
located beneath the thermostat housing at the front
of the intake manifold (Fig. 22).
The thermostat is a moveable sleeve type.
Coolant leakage into the pellet container will cause
the thermostat to fail in the open position. Thermo-
stats very rarely stick. Do not attempt to free a ther-
mostat with a prying device.
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 longer engine
warmup time, unreliable warmup performance,
increased exhaust emissions and crankcase condensa-
tion that 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
Allgasoline powered modelsare equipped with
On-Board Diagnostics for certain cooling system com-
ponents. Refer to On-Board Diagnostics (OBD) in the
Diagnosis section of this group for additional infor-
mation. If the powertrain control module (PCM)
detects low engine coolant temperature, it will record
a Diagnostic Trouble Code (DTC) in the PCM mem-
ory. Do not change a thermostat for lack of heat as
indicated by the instrument panel gauge or by poor
heater performance unless a DTC is present. Refer to
the Diagnosis section of this group for other probable
causes. For other DTC numbers, (Refer to 25 - EMIS-
SIONS CONTROL - DESCRIPTION).
The DTC can also be accessed through the DRB
scan tool. Refer to the appropriate Powertrain Diag-
nostic Procedures information for diagnostic informa-
tion and operation of the DRB scan tool.
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.
If the thermostat is being replaced, be sure that
the replacement is the specified thermostat for the
vehicle model and engine type.
A rubber lip-type seal with a metal shoulder is
pressed into the intake manifold beneath the thermo-
stat (Fig. 23).
(1) Disconnect negative battery cable at battery.
(2) Drain cooling system until coolant level is
below thermostat (Refer to 7 - COOLING - STAN-
DARD PROCEDURE).
(3) Remove the two support rod mounting bolts
and remove support rod (intake manifold-to-genera-
tor mount) (Fig. 24).
Fig. 22 ThermostatÐ8.0L V-10 Engine
1 - COOLANT TEMP. SENSOR (FOR PCM)
2 - HEATER SUPPLY FITTING
3 - BOLTS (6)
4 - HOUSING WITH INTEGRAL SEAL
5 - THERMOSTAT
6 - RUBBER LIP SEAL
7 - TEMP. GAUGE SENDING UNIT
BR/BEENGINE 7 - 51

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 replacementis necessary, use only an original equipment clamp
with a matching number or letter.
(4) Remove upper radiator hose clamp. Remove
upper radiator hose at thermostat housing.
(5) Disconnect the wiring connectors at both of the
sensors located on thermostat housing.
(6) Remove six thermostat housing mounting bolts,
thermostat housing and thermostat.
INSTALLATION
(1) Clean mating areas of intake manifold and
thermostat housing.
(2) Check the condition (for tears or cracks) of the
rubber thermostat seal located in the intake manifold
(Fig. 23) (Fig. 25). The thermostat should fit snugly
into the rubber seal.
(3) If seal replacement is necessary, coat the outer
(metal) portion of the seal with MopartGasket
Maker. Install the seal into the manifold using Spe-
cial Seal Tool number C-3995-A with handle tool
number C-4171.
Fig. 23 Thermostat SealÐ8.0L V-10 Engine
1 - METAL SEAL SHOULDER
2 - RUBBER LIP SEAL
3 - THERMOSTAT OPENING
Fig. 24 Support RodÐ8.0L V-10 Engine
1 - BOLTS
2 - SUPPORT ROD
Fig. 25 ThermostatÐ8.0L V-10 Engine
1 - COOLANT TEMP. SENSOR (FOR PCM)
2 - HEATER SUPPLY FITTING
3 - BOLTS (6)
4 - HOUSING WITH INTEGRAL SEAL
5 - THERMOSTAT
6 - RUBBER LIP SEAL
7 - TEMP. GAUGE SENDING UNIT
7 - 52 ENGINEBR/BE
ENGINE COOLANT THERMOSTAT - 8.0L (Continued)

(4) Install thermostat into recessed machined
groove on intake manifold (Fig. 25).
(5) Install thermostat housing (Fig. 25).
(6) Install housing-to-intake manifold bolts.
Tighten bolts to 25 N´m (220 in. lbs.) torque.
CAUTION: Housing bolts should be tightened
evenly to prevent damage to housing and to pre-
vent leaks.
(7) Connect the wiring to both sensors.
(8) Install the upper radiator hose and hose clamp
to thermostat housing.
(9) Install support rod.
(10) Fill cooling system (Refer to 7 - COOLING -
STANDARD PROCEDURE).
(11) Connect negative battery cable to battery.
(12) Start and warm engine. Check for leaks.
ENGINE COOLANT
THERMOSTAT - 5.9L DIESEL
DESCRIPTION
CAUTION: Do not operate an engine without a ther-
mostat, except for servicing or testing. An engine
with the thermostat removed will operate in the
radiator bypass mode, causing an overheat condi-
tion.
The thermostat of the 5.9L diesel engine is located
in the front of the cylinder head, underneath the
water outlet connector (Fig. 26).
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 longer engine
warmup time, unreliable warmup performance,
increased exhaust emissions and crankcase condensa-
tion that 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
The cooling system used with the diesel engine
provides the extra coolant capacity and extra cooling
protection needed for higher GVWR (Gross Vehicle
Weight Rating) and GCWR (Gross Combined Weight
Rating) vehicles.
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.
Fig. 26 ThermostatÐ5.9L DieselÐTypical
1 - WATER OUTLET CONNECTOR
2 - THERMOSTAT HOUSING
3 - THERMOSTAT
BR/BEENGINE 7 - 53
ENGINE COOLANT THERMOSTAT - 8.0L (Continued)

INSPECTION
Inspect the radiator side tanks for cracks, broken
or missing fittings also inspect the joint where the
tanks seam up to the radiator core for signs of leak-
age and/or deteriorating seals.
Inspect radiator core for corroded, bent or missing
cooling fins. Inspect the core for bent or damaged
cooling tubes.
INSTALLATION
(1) Position fan shroud over the fan blades rear-
ward towards engine.
(2) Install rubber insulators to alignment dowels
at lower part of radiator.
(3) Lower the radiator into position while guiding
the two alignment dowels into lower radiator sup-
port. Different alignment holes are provided in the
lower radiator support for each engine application.
(4) Install two upper radiator mounting bolts.
Tighten bolts to 11 N´m (95 in. lbs.) torque.
(5) Position the rubber shields to the sides of radi-
ator. Install the plastic clips retaining the rubber
shields to the sides of radiator.
(6) Connect both radiator hoses and install hose
clamps.
(7) Install windshield washer reservoir tank.
(8) Position fan shroud to flanges on sides of radi-
ator. Install fan shroud mounting bolts (Fig. 34).
Tighten bolts to 6 N´m (50 in. lbs.) torque.
(9) Install coolant reserve/overflow tank hose to
radiator filler neck nipple.
(10) Install coolant reserve/overflow tank to fan
shroud (fits into T-slots on shroud).
(11) Install battery negative cables.
(12) Position heater controls tofull heatposition.
(13) Fill cooling system with coolant (Refer to 7 -
COOLING - STANDARD PROCEDURE).
(14) Operate engine until it reaches normal tem-
perature. Check cooling system fluid levels.
RADIATOR - 8.0L
DESCRIPTION
The radiator is a aluminum cross-flow design with
horizontal tubes through the radiator core and verti-
cal plastic side tanks (Fig. 36).
This radiator contains an internal transmission oil
cooler only on the V-10 gas engine and the 5.9L die-
sel engine combinations.
OPERATION
The radiator supplies sufficient heat transfer using
the cooling fins interlaced between the horizontal
tubes in the radiator core to cool the engine.
DIAGNOSIS AND TESTINGÐRADIATOR
COOLANT FLOW
Use the following procedure to determine if coolant
is flowing through the cooling system.
(1) Idle engine until operating temperature is
reached. If the upper radiator hose is warm to the
touch, the thermostat is opening and coolant is flow-
ing to the radiator.
WARNING: HOT, PRESSURIZED COOLANT CAN
CAUSE INJURY BY SCALDING. USING A RAG TO
COVER THE RADIATOR PRESSURE CAP, OPEN
RADIATOR CAP SLOWLY TO THE FIRST STOP. THIS
WILL ALLOW ANY BUILT-UP PRESSURE TO VENT
TO THE RESERVE/OVERFLOW TANK. AFTER PRES-
SURE BUILD-UP HAS BEEN RELEASED, REMOVE
CAP FROM FILLER NECK.
(2) Drain a small amount of coolant from the radi-
ator until the ends of the radiator tubes are visible
through the filler neck. Idle the engine at normal
operating temperature. If coolant is flowing past the
exposed tubes, the coolant is circulating.
REMOVAL
(1) Disconnect battery negative cables.
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.
Fig. 36 Cross Flow RadiatorÐTypical
1 - COOLING TUBES
2 - TANKS
7 - 60 ENGINEBR/BE
RADIATOR - 5.9L (Continued)

(2) Install rubber insulators to alignment dowels
at lower part of radiator.
(3) Lower the radiator into position while guiding
the two alignment dowels into lower radiator sup-
port. Different alignment holes are provided in the
lower radiator support for each engine application.
(4) Install two upper radiator mounting bolts.
Tighten bolts to 11 N´m (95 in. lbs.) torque.
(5) Connect both radiator hoses and install hose
clamps.
(6) Install windshield washer reservoir tank.
(7) Position fan shroud to flanges on sides of radi-
ator. Install fan shroud mounting bolts (Fig. 37).
Tighten bolts to 6 N´m (50 in. lbs.) torque.
(8) Install coolant reserve/overflow tank hose to
radiator filler neck nipple.
(9) Connect the overflow hose to the radiator.
(10) Install battery negative cables.
(11) Position heater controls tofull heatposition.
(12) Fill cooling system with coolant (Refer to 7 -
COOLING - STANDARD PROCEDURE).
(13) Operate engine until it reaches normal tem-
perature. Check cooling system fluid levels.
RADIATOR - 5.9L DIESEL
DESCRIPTION
The radiator is a aluminum cross-flow design with
horizontal tubes through the radiator core and verti-
cal plastic side tanks (Fig. 39).
This radiator contains an internal transmission oil
cooler only on the V-10 gas engine and the 5.9L die-
sel engine combinations.
OPERATION
The radiator supplies sufficient heat transfer using
the cooling fins interlaced between the horizontal
tubes in the radiator core to cool the engine.
DIAGNOSIS AND TESTINGÐRADIATOR
COOLANT FLOW
Use the following procedure to determine if coolant
is flowing through the cooling system.
(1) Idle engine until operating temperature is
reached. If the upper radiator hose is warm to the
touch, the thermostat is opening and coolant is flow-
ing to the radiator.
WARNING: HOT, PRESSURIZED COOLANT CAN
CAUSE INJURY BY SCALDING. USING A RAG TO
COVER THE RADIATOR PRESSURE CAP, OPEN
RADIATOR CAP SLOWLY TO THE FIRST STOP. THIS
WILL ALLOW ANY BUILT-UP PRESSURE TO VENT
TO THE RESERVE/OVERFLOW TANK. AFTER PRES-SURE BUILD-UP HAS BEEN RELEASED, REMOVE
CAP FROM FILLER NECK.
(2) Drain a small amount of coolant from the radi-
ator until the ends of the radiator tubes are visible
through the filler neck. Idle the engine at normal
operating temperature. If coolant is flowing past the
exposed tubes, the coolant is circulating.
REMOVAL
(1) Disconnect both battery negative cables.
Remove the nuts retaining the positive cable to the
top of radiator. Position positive battery cable to rear
of vehicle.
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.
(2) Drain the cooling system (Refer to 7 - COOL-
ING - 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). SNAP-ON CLAMP TOOL (NUMBER HPC-20)
MAY BE USED FOR LARGER CLAMPS. ALWAYS
WEAR SAFETY GLASSES WHEN SERVICING CON-
STANT TENSION CLAMPS.
Fig. 39 Cross Flow RadiatorÐTypical
1 - COOLING TUBES
2 - TANKS
7 - 62 ENGINEBR/BE
RADIATOR - 8.0L (Continued)

CLEANING
Clean radiator fins are necessary for good heat
transfer. The radiator and air conditioning fins
should be cleaned when an accumulation of debris
has occurred. With the engine cold, apply cold water
and compressed air to the back (engine side) of the
radiator to flush the radiator and/or A/C condenser of
debris.
INSPECTION
Inspect the radiator side tanks for cracks, broken
or missing fittings also inspect the joint where the
tanks seam up to the radiator core for signs of leak-
age and/or deteriorating seals.
Inspect radiator core for corroded, bent or missing
cooling fins. Inspect the core for bent or damaged
cooling tubes.
INSTALLATION
(1) Position fan shroud over the fan blades rear-
ward towards engine.
(2) Install rubber insulators to alignment dowels
at lower part of radiator.
(3) Lower the radiator into position while guiding
the two alignment dowels into lower radiator sup-
port. Different alignment holes are provided in the
lower radiator support for each engine application.
(4) Install two upper radiator mounting bolts.
Tighten bolts to 11 N´m (95 in. lbs.) torque.
(5) Connect both radiator hoses and install hose
clamps.
(6) Connect transmission cooler lines to radiator
tank. Inspect quick connect fittings for debris and
install until an audible ªclickº is heard. Pull apart to
verify connection.
(7) Install windshield washer reservoir tank.
(8) Position fan shroud to flanges on sides of radi-
ator. Install fan shroud mounting bolts (Fig. 41).
Tighten bolts to 6 N´m (50 in. lbs.) torque.
(9) Install metal clips to top of fan shroud.
(10) Install coolant reserve/overflow tank hose to
radiator filler neck nipple.
(11) Install coolant reserve/overflow tank to fan
shroud (fits into T-slots on shroud).
(12) Install battery negative cables.
(13) Install positive battery cable to top of radia-
tor. Tighten radiator-to-battery cable mounting nuts.
(14) Position heater controls tofull heatposition.
(15) Fill cooling system with coolant (Refer to 7 -
COOLING - STANDARD PROCEDURE).
(16) Operate engine until it reaches normal tem-
perature. Check cooling system and automatic trans-
mission (if equipped) fluid levels.
RADIATOR PRESSURE CAP
DESCRIPTION
Radiators are equipped with a pressure cap, which
releases pressure at some point within a range of
97-124 kPa (14-18 psi). The pressure relief point (in
pounds) is engraved on top of cap.
The cooling system will operate at pressures
slightly above atmospheric pressure. This results in a
higher coolant boiling point allowing increased radi-
ator cooling capacity.
A rubber gasket seals radiator filler neck to pre-
vent leakage. This is done to keep system under
pressure. It also maintains vacuum during coolant
cool-down allowing coolant to return from reserve/
overflow tank.
OPERATION
The cap (Fig. 43) contains a spring-loaded pressure
relief valve that opens when system pressure reaches
release range of 97-124 kPa (14-18 psi).
A vent valve in the center of cap allows a small
coolant flow through cap when coolant is below boil-
ing temperature. The valve is completely closed when
boiling point is reached. As the coolant cools, it con-
tracts and creates a vacuum in the cooling system.
This causes the vacuum valve to open and coolant in
the reserve/overflow tank to be drawn through its
connecting hose into radiator. If the vacuum valve is
stuck shut, the radiator hoses will collapse on cool-
down. Clean the vent valve (Fig. 43).
Fig. 43 Radiator Pressure Cap and Filler NeckÐ
Typical
1 - STAINLESS-STEEL SWIVEL TOP
2 - RUBBER SEALS
3 - VENT VALVE
4 - RADIATOR TANK
5 - FILLER NECK
6 - OVERFLOW NIPPLE
7 - MAIN SPRING
8 - GASKET RETAINER
7 - 64 ENGINEBR/BE
RADIATOR - 5.9L DIESEL (Continued)