Dodge Ram Truck 1500-2500-3500. Manual - part 239

On the 3.7L/4.7L engine the thermostat is designed to
block the flow of the coolant bypass journal by 50%
instead of completely blocking the flow. This design
controls coolant temperature more accurately.

The same thermostat is used for winter and summer
seasons. An engine should not be operated without a
thermostat, except for servicing or testing. Operating
without a thermostat causes other problems. These
are: longer engine warm-up time, unreliable warm-up
performance, increased exhaust emissions and crank-
case condensation. This condensation can result in
sludge formation.

5.9L DIESEL

CAUTION: Do not operate an engine without a
thermostat, except for servicing or testing. An
engine with the thermostat removed will operate in
the radiator bypass mode, causing an overheat
condition.

The thermostat of the 5.9L diesel engine is located in
the front of the cylinder head, underneath the thermo-
stat housing.

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ENGINE

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OPERATION

3.7L/4.7L/5.7L ENGINE

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.

8.3L ENGINE

The thermostat’s primary purpose is to maintain engine temperature in a range that will provide satisfactory engine
performance and emission levels under all expected driving conditions.

The thermostat is unique because the center does not open and close like a conventional thermostat; it works like
a sliding sleeve. The outside sleeve moves, directing coolant flow through the engine block or through the bypass
passages back to the water pump. During warm-up below 85°C (185°F), the thermostat is seated in the retracted
position. This will allow the coolant to flow into the bypass passage, and back to the water pump. At 85°C (185°F)
the thermostat begins to open, allowing coolant to flow through both the bypass and the radiator. At 97°C (207°F)
the thermostat will fully open, blocking the path to the bypass, allowing all coolant to flow through the radiator.

DIAGNOSIS AND TESTING

THERMOSTAT

ON-BOARD DIAGNOSTICS - GAS ENGINES

All gasoline powered models are equipped with On-Board Diagnostics for certain cooling system components.
Refer to On-Board Diagnostics (OBD) in the Diagnosis section of this group for additional information. If the pow-
ertrain control module (PCM) detects low engine coolant temperature, it will record a Diagnostic Trouble Code
(DTC) in the PCM memory. 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.

The DTC can also be accessed through the DRBIII

scan tool. Refer to the appropriate Powertrain Diagnostic Pro-

cedures information for diagnostic information and operation of the DRBIII

scan tool.

5.9L DIESEL ENGINE

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 affect warm up or cold weather operating characteristics if the thermostat is operating
properly. This is because coolant will be held in the engine until it reaches the thermostat “set” 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 temperature gauge readings for
diesel versus gasoline engines may, at times be normal.

Typically, complaints of low engine coolant temperature are observed as low heater output when combined with cool
or cold outside temperatures.

To help promote faster engine warm-up, the electric 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.

A “Cold Weather Cover” 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
literature supplied with the cover for additional information.

For engines equipped with exhaust brakes, this device can be used to aid engine warm-up while the engine is
idling.

1. To determine if the thermostat is defective, it must be removed from the vehicle (Refer to 7 - COOLING/ENGINE/

ENGINE COOLANT THERMOSTAT - REMOVAL).

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2. After the thermostat has been removed, examine the thermostat and inside of thermostat housing for contami-

nants. If contaminants are found, the thermostat may already be in a “stuck open” position. Flush the cooling
system before replacing thermostat (Refer to 7 - COOLING - STANDARD PROCEDURE).

3. Place the thermostat into a container filled with water.

4. Place the container on a hot plate or other suitable heating device.

5. Place a commercially available radiator thermometer into the water.

6. Apply heat to the water while observing the thermostat and thermometer.

The thermostat will begin to open at 85.5 - 89.4°C. (186 - 193°F ). If the valve starts to move before this tem-

perature is reached, it is opening too early. Replace thermostat. The thermostat should be fully open (valve will
stop moving) at 97°C (207°F). If the valve is still moving when the water temperature reaches 97°C (207°F), it is
opening too late. Replace thermostat. If the valve refuses to move at any time, replace thermostat.

REMOVAL

3.7L/4.7L ENGINE

WARNING: DO NOT LOOSEN THE RADIATOR
DRAINCOCK WITH THE COOLING SYSTEM HOT
AND PRESSURIZED. 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.

1. Disconnect the negative battery cable.

2. Drain the cooling system (Refer to 7 - COOLING -

STANDARD PROCEDURE).

3. Raise and support the vehicle.

4. Remove the splash shield.

5. Remove the lower radiator hose clamp and the

lower radiator hose at the thermostat housing.

6. Remove the thermostat housing mounting bolts,

thermostat housing and thermostat.

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ENGINE

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5.7L ENGINE

WARNING: DO NOT LOOSEN THE RADIATOR
DRAINCOCK WITH THE COOLING SYSTEM HOT
AND PRESSURIZED. 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.

1. Disconnect the negative battery cable.

2. Drain the cooling system

3. Remove the radiator hose clamp (3) and radiator

hose (4) at the thermostat housing (2).

4. Remove the thermostat housing mounting bolts,

thermostat housing and thermostat.

5.9L DIESEL ENGINE

WARNING: DO NOT LOOSEN THE RADIATOR
DRAINCOCK WITH THE SYSTEM HOT AND PRES-
SURIZED. SERIOUS BURNS FROM THE COOLANT
CAN OCCUR.

Do not waste reusable coolant. If the solution is clean,
drain the coolant into a clean container for reuse.

1. Disconnect the battery negative cables.

2. Drain cooling system until coolant level is below

thermostat (Refer to 7 - COOLING - STANDARD
PROCEDURE).

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ENGINE

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