How to Change a Cummins 12 Valve Thermostat

Step-by-Step Guide

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   Step 1: Disconnect the negative (black) cable from the engine's battery.

   Close the container as soon as liquid stops draining from the truck.,, Place the hose to the side so it doesn't cover the alternator.,, Take out the engine lifting bracket, followed by the thermostat with its seal., Ensure that the tong on the thermostat is lined up with the slot of the housing.
   
   Having proper alignment allows air to pass through the jiggle pins and through the radiator neck. , Check that the seal is installed with the beveled side facing outward., Reconnect the upper radiator hose to the thermostat cover., Tighten the upper bolt to 18 foot (5.5 m) pounds (24 Nm) and the lower bolt to 32 foot (9.8 m) pounds (43 Nm)., Run your engine until the thermostat opens., If any leaks are found, turn off your diesel engine and check bolts and hoses for secure fits., Recheck coolant levels.
   
   Add more antifreeze with the thermostat plug removed until it overflows the plug hole.,
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   Step 2: Drain the engine's coolant into a container.

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   Step 3: Lift the belt tensioner with a 3/8-inch (9.53 mm) breaker bar and remove the drive belt.

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   Step 4: Disconnect the engine's upper radiator hose from the thermostat's cover.

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   Step 5: Loosen the alternator's mounting bolts and lower the alternator so it is no longer blocking access to the thermostat.

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   Step 6: Unfasten the thermostat's housing.

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   Step 7: Mount the new thermostat to its cover.

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   Step 8: Remount the engine lifting bracket

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   Step 9: new thermostat and seal.

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    Step 10: Place the thermostat housing in the correct position in the engine and use a torque wrench to tighten the bolts to 18 foot (5.5 m) pounds (24 Nm).

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    Step 11: Place the alternator back into its correct position.

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    Step 12: Replace the drive belt and reconnect the negative battery cable.

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    Step 13: Fill the radiator with coolant and check for leaks.

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    Step 14: Turn off the engine and let the vehicle cool.

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    Step 15: Put the thermostat plug back into place and top off the radiator.

Detailed Guide

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