Heater Core Flush

by: JayTheSnork


if you're singing the "I ain't got no heat" blues, it may be time to flush your heater core. the pix included here are from my Audi, but we all know Audi and VW are brother and sister cars - in this case, the pix are of a V6, but the heater core connections off the motor are similar to VW 1.8T as well.



  • pliers
  • screwdriver
  • dark colored bucket
  • hose
  • safety goggles
  • copper tubing(bent in a U-shape to stuff into the hoses)


  • 6 feet of 3/4" inside diameter hose
  • three screw-type hose clamps
  • corks

I'm not responsible for any damage you do to your car while following these directions.

1. using pliers, loosen the clamps and push them to the firewall.

2. using those same pliers, pull both the hoses off the firewall nipples. some coolant will escape, so don't get it into your eyes!

3. plug the hoses and clamp them off to prevent air from getting into the lines. I plugged my lines with a length of copper tubing bent in a U shape, but you can use almost anything- corks, for example. (I pulled the battery to clean the drain under it at the same time, so you'll see a battery cable laying loose in the pix.)

4. cut and attach a one foot length of 3/4 inch hose to the input side of the heater core. it will be a tough fit, so you may want to lubricate the inside of the hose. at the open end of the hose, push a cheap garden sprayer into the end of the hose. connect your garden hose to the sprayer.

5. attach the remaining 5 feet of 3/4 inch hose to the return line of the heater. drape it off the front of the car into a bucket. I used a dark colored bucket because it makes it easier to see the calcified crap and flakes as that stuff comes out of the heater core.

I used one of these hose sprayers:

6. turn on the hose and force the old coolant out of the core - be careful not to use all the pressure that is available, as you could potentially cause a leak in the core! fill the bucket with the old coolant and crap, then and dispose of properly - G12 is probably enticing to animals to drink it (like other coolants), and it might kill or sicken them if they ingest it.

7. turn off the water, and empty the bucket, and do it all over again repeatedly until no more flakes of calcification are present in the bucket. my most recent undertaking took about 25 x 5 gallon buckets of water before it was clear of flakes.

8. disconnect your flushing hoses, and reconnect the heater hoses. put the clamp on the inlet (right as you are facing the firewall from the front of the car) side of the core, and leave the clamp off the outlet side. make sure the outlet side weep hole is not on the nipple - in other words, do not fully push that hose onto the nipple, because you need to allow the air to escape.

9. start the car, and let it get to normal operating temperature.

10. rev the car to increase the pressure on the cooling system; you'll be forcing any air out, and as soon as a jet of coolant shoots out of the weep hole, stop revving the car, push the outlet hose fully onto the nipple, and turn the car off.

11. clamp the outlet hose.

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