Flushing Heater Core Backwards

• 1). Park the car in a safe area and allow the engine to cool. When the radiator cap and engine block feel cool, the car is safe to work on.
  
  
• 2). Identify the heater hoses. Heater hoses are flexible rubber lines that carry coolant from the engine to the heater core. The hoses are easiest to find where they attach to the heater core at the firewall. The firewall is located between the engine and passenger compartment.
  
  
• 3). Follow the hoses from the firewall to where they attach to the engine. One hose will attach near the water pump, this is the outlet hose. The other hose will attach near the thermostat housing, this is the inlet hose.
  
  
• 4). Place buckets or pans under the vehicle where these hoses attach to the engine to catch leaked coolant. Remove clamps holding the hoses to their mounts on the engine. Clamps will either be spring loaded or secured by a screw. Remove spring clamps by pinching the tabs together with pliers and sliding the clamp away from the connection. Remove screw clamps by unscrewing the screw until the clamp loosens and sliding the clamp away from the connection.
  
  
• 5). Lift ends of hoses to prevent unnecessary loss of engine coolant. Place inlet heater hose into a bucket.
  
  
• 6). Use garden hose to spray water into the outlet hose. Allow water to flow through heater core, out the inlet hose, and into bucket. Do not tightly seal the garden hose to the outlet hose. Residential water pressure may damage the heater core, causing a leak.
  
  
• 7). Secure heater hoses back to their original position. Dry outside of hose and other engine components with rags. Clean up any engine coolant that spilled onto the floor.
  
  
• 8). Run vehicle until warm to circulate the engine coolant. Allow engine to cool. Refill coolant system with mixture of antifreeze and distilled water per instructions on the antifreeze container.