Bleeding Air from the Cooling System

Normally, all but about 1.5 qt (1.4 liters) of coolant drain out of the cooling system when it is drained. If approximately half of the Cooling System Capacity (see Specifications Chapter) seems to fill the cooling system after it has been drained, air has been trapped in the block. Bleed the air out of the block using the following procedure:

Important Do not start the engine without bleeding the air out of the block.
Important If an engine runs with air trapped in the block, the engine may be damaged. The high water temperature switch may not protect an engine that has air trapped in the block, because the high water temperature switch is designed to protect an engine from overheating due to failures in the cooling system.

  1. Pour coolant into the system until it appears to be full. The amount of coolant that goes back into the system is approximately equal to the amount of coolant that came out of the system.

  2. Start the engine. Monitor the coolant temperature with the unit engine coolant temperature gauge, or by using a non-contact thermometer pointed at the thermostat housing in the location of the high water temperature switch or sensor. When the temperature reaches 150 F (66 C), shut the engine off for 2 minutes. This allows time for the thermostat to heat soak and open fully, ensuring that any remaining air will be purged out of the engine block when the engine is restarted.

  3. Restart the engine and run it in low speed. Remove the cap from the expansion tank and slowly pour coolant into expansion tank until it is full, then reinstall the expansion tank cap.

  4. Repeat steps 2 and 3 until the coolant level stabilizes.

Parent topic: Engine Cooling System