Thermostat

Replace the thermostat and housing gasket on the 6.7L Cummins diesel engine to restore proper engine temperature regulation.

Warnings

Tools required

Parts

• Thermostat assembly × 1 — Use OEM Mopar thermostat
• Thermostat housing gasket or O-ring × 1 — Use OEM specification
• Hose clamps (if damaged) × 2 — Worm gear or spring type as required

Fluids

• Mopar OAT Coolant (Purple) — 2 qt

Preparation

1. Ensure engine is completely cold before beginning work
2. Park vehicle on level ground and engage parking brake
3. Disconnect negative battery cable to prevent fan engagement
4. Place drain pan beneath lower radiator hose connection point
5. Remove engine cover if equipped

Procedure

1. 1

   Drain cooling system
   Locate the radiator petcock or lower radiator hose. Open the petcock or carefully loosen the lower radiator hose clamp and slide it back. Allow coolant to drain into the catch pan. If reusing coolant, ensure it is clean and properly tested for freeze protection. Once drained, close petcock or temporarily reconnect hose.
2. 2

   Access thermostat housing
   The thermostat housing is located on the front driver side of the engine block, near the water pump. Remove the upper radiator hose from the thermostat housing by loosening the hose clamp and carefully twisting the hose to break the seal. Slide the hose off the housing outlet.
3. 3

   Disconnect coolant temperature sensor
   Locate the coolant temperature sensor on the thermostat housing. Press the release tab and disconnect the electrical connector. Move the wiring harness aside to provide clearance for housing removal.
4. 4

   Remove thermostat housing
   Remove the thermostat housing mounting bolts using a socket and ratchet. There are typically 2-3 bolts securing the housing to the engine block. Carefully pull the housing away from the engine. If stuck, gently tap with a soft mallet. Remove the old thermostat and note its orientation with the spring side facing into the engine.
   Torque spec

   Thermostat Housing Bolts15 Nm (11 lb-ft)
5. 5

   Clean mating surfaces
   Thoroughly clean the thermostat housing mating surface on the engine block and the housing itself. Remove all traces of old gasket material, corrosion, and debris using a scraper. Be careful not to gouge the aluminum surfaces. Wipe clean with shop towels and inspect for cracks or damage.
6. 6

   Install new thermostat
   Install the new thermostat into the engine block recess with the spring side facing INTO the engine block. Ensure it seats properly in the recess. Install the new gasket or O-ring onto the thermostat housing, ensuring it is properly positioned in the groove.
7. 7

   Reinstall thermostat housing
   Position the thermostat housing over the thermostat, aligning the bolt holes. Install the housing bolts hand-tight first to ensure proper alignment. Torque the thermostat housing bolts in a criss-cross pattern to specification to ensure even sealing pressure.
   Torque spec

   Thermostat Housing Bolts15 Nm (11 lb-ft)
8. 8

   Reconnect coolant temperature sensor
   If the coolant temperature sensor was removed, apply a thin coating of thread sealant to the threads. Install the sensor into the thermostat housing and torque to specification. Reconnect the electrical connector firmly until it clicks.
   Torque spec

   Coolant Temperature Sensor20 Nm (15 lb-ft)
9. 9

   Reconnect upper radiator hose
   Slide the upper radiator hose onto the thermostat housing outlet. Ensure the hose is fully seated on the fitting. Position the hose clamp approximately 1/4 inch from the end of the hose and tighten to specification.
10. 10

    Refill cooling system
    Locate the cooling system bleed screw on top of the thermostat housing or nearby coolant passage. Open the bleed screw approximately 2-3 turns. Fill the cooling system slowly through the degas bottle or radiator cap with Mopar Purple OAT coolant. Continue filling until coolant flows from the bleed screw without air bubbles. Close the bleed screw to specification.
    ℹ️Fill slowly to minimize air entrapment. Use a 50/50 mix of coolant and distilled water or pre-mixed coolant.
11. 11

    Bleed air from system
    With the degas bottle filled to the cold fill line, reconnect the negative battery cable. Start the engine and allow it to run at idle with the heater set to maximum temperature. Monitor the coolant level and add as necessary. Watch for coolant circulation in the degas bottle. Run until the thermostat opens and cooling fan cycles on, indicating proper temperature regulation.
    ⚠Monitor temperature gauge closely. If temperature exceeds normal range, shut off engine immediately and recheck for air pockets.
12. 12

    Final inspection and top-off
    Allow engine to cool completely. Recheck coolant level in the degas bottle and top off to the cold fill line if necessary. Inspect all connections for leaks, particularly around the thermostat housing and hose connections. Clean any spilled coolant from the engine bay.

Reassembly

1. Reinstall engine cover if previously removed
2. Ensure all tools are removed from engine compartment
3. Dispose of used coolant properly at a recycling facility

Verification

• Start engine and verify no coolant leaks at thermostat housing or hose connections
• Confirm engine reaches normal operating temperature (approximately 180-200°F) within 10-15 minutes
• Verify cooling fan cycles on at proper temperature
• Check that heater produces hot air at idle and under load
• Verify coolant level remains stable in degas bottle after several heat cycles
• Scan for diagnostic trouble codes related to coolant temperature to ensure proper sensor operation

Related trouble codes on this vehicle

Codes that commonly send this job to the bay — tap one for symptoms, causes, and diagnostic steps.

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