Back Flushing-Heater Core

All engine cooling system flushing and back-flushing procedures must include a separate back-flushing of the heater or A/C system heater core, after the flushing or back-flushing 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.

CAUTION: The heater core must be back-flushed separately from the engine cooling system for proper back-flush water flow direction through the heater core.

The correct heater core back-flushing procedure is as follows:
1. Disconnect the heater core outlet heater water hose and install a female garden hose-end fitting adapter in the end of the outlet heater water hose. Secure with a hose clamp.
2. Connect the female garden hose end of the outlet heater water hose to the male end of a water supply garden hose.
3. Disconnect the heater core inlet heater water hose and allow to drain into a suitable container.
4. Turn the water supply valve on and off several times so that the surge action will help to dislodge large stubborn particles from the heater core tubes. Allow full water pressure to flow for approximately five minutes.
5. Remove the hose clamp and female garden hose-end adapter from the end of the outlet heater water hose and reconnect the outlet heater water hose.
6. Connect the inlet heater water hose.
7. Fill the engine cooling system using the specified coolant mixture.
8. Test the system for proper heater performance with the specified engine cooling system conditions.