Heater Core Backflushing

All engine cooling system flushing and backflushing procedures must include a separate backflushing of the heater or A/C system heater core, after the flushing or backflushing of the engine cooling system, to prevent engine cooling system particles from clogging the heater core tubes and reducing (or eliminating) coolant flow through the heater core. The heater core must be backflushed separately from the engine cooling system for proper backflush water flow direction through the heater core.

The correct heater core backflushing procedure is as follows:

1. Disconnect the heater core outlet heater hose from the water pump fitting and install a female garden hose-end fitting adapter in the end of the outlet heater hose. Secure with a hose clamp.

2. Connect the female garden hose end of the outlet heater hose to the male end of a water supply garden hose.

3. Disconnect the heater core inlet heater hose from the engine block fitting and allow to drain into a suitable container.

4. If a water valve is installed in the heater core inlet heater hose, check to be certain the water valve is open (no vacuum).

5. Turn the water supply valve on/off several times so that the surge action will help to dislodge larger stubborn particles from the heater core tubes. Allow full water pressure to flow for approximately five minutes.

6. If a water valve is installed in the heater core inlet heater hose, apply vacuum to the water valve vacuum motor to ensure proper operation of the water valve and proper closure with no water leakage. Replace the water valve if required.

7. Remove the hose clamp and female garden hose-end adapter from the end of the outlet heater hose and reconnect the outlet heater hose onto the water pump fitting.

8. Connect the inlet heater hose onto the engine block fitting.

9. Fill the cooling system, as described in this Section using the specified coolant mixture.

10. Test the system for proper heater performance with the specified engine cooling system conditions.