Draining, Flushing And Replacement Of Diesel Coolant

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Open the air bleed valve in the engine coolant outlet (thermostat housing). See Fig 1.
Fill the surge tank bottle until coolant comes out of the air bleed valve.
ON VEHICLES WITH REAR HEATER, close the air bleed valve. Start the engine and bring the engine speed to 2000 RPM for 2 to 3 minutes to flush any air for rear heater. Shut off the engine and open the air bleed valve. Fill the surge tank until coolant comes out the air bleed valve.
Close the air bleed valve and install pressure cap on the surge tank.
Monitor the cold coolant level in the surge tank. Add coolant as needed to bring the coolant level to the "Full Cold" mark.
Verify there are no leaks.

Fig 1: Coolant Air Bleed Valve Location (Diesel)

Courtesy of GENERAL MOTORS CORP.

NOTE: For more information regarding Diesel Idle Speed Adjustments refer to the ADJUSTMENTS - 6.5L DIESEL article in the ENGINE PERFORMANCE section.