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Heater core backflush w/ pics

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Old 11-30-2008, 07:41 PM   #1
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Default Heater core backflush w/ pics

After being without heat since early spring, I decided it was time to set things right. Using this post as a guide, I went to Home Depot and bought 10' of 3/4" id tubing to make my life easier. As I later discovered, 7/8" would have been much easier to work with.

Remove the rear firewall rubber gasket, cover, and plastic tray/pollen filter and passenger side windshield cover. Get the wiper arms vertical. The engine bay should now look like this:




Wedge the driver side wiper cover up on top of the wipers to get it out of the way. Remove the corrugated hose cover (it's split on the back) to expose the lines running into and out from the heater core. You should now be looking at this:




Slide your tubing over the inlet side and run the other end down to a bucket of some sort. You'll need 4-5'.






Slide a shorter length of tubing over the outlet side (1-2'). I used a brass hose nozzle that increases flow as you twist it because it sealed fairly well against the end of the hose. Turn on the water flow (not too hard as the heater core is a bitch to replace) and watch the gunk come out. Keep flushing until the water coming out is clear.

Reverse the hose and forward flush, again making sure the water coming out is clear. Now is probably a good time to drain, flush, and bleed your whole cooling system. Reverse the removal steps to get things back together. Here's what I was left with:



...oh yeah, and HEAT.
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Old 11-30-2008, 08:31 PM   #2
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Default Did the same last week except without all the hoses... just undid one of the hoses on the

client's 2002 A4 and let it flush for 10 minutes on the driveway... now she has heat again as well :-)
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Old 12-01-2008, 04:08 AM   #3
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nice!
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Old 12-01-2008, 08:12 AM   #4
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I need to do the same, but whats the risk of causing a leak in the heater core?
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Old 12-01-2008, 09:10 AM   #5
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Heater core is inside the car... 8 hours later you can swap it out, after taking dash out :-)
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Old 12-01-2008, 09:35 AM   #7
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Default question...

was the coolant in the resevoir tank the same color as the 'gunk'?
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Old 12-01-2008, 10:43 AM   #8
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Default Yes, I still need to replace the radiator

Flushing it out produced more of the same. Maybe I'll get to that this winter in my new garage. For the moment, I can live with it. Gotta stay warm.
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Old 12-01-2008, 11:42 AM   #9
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Default ok...

so its safe to assume if your resevoir looks like virgin G12, flushing the heater core might not be needed.
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Old 12-01-2008, 12:34 PM   #10
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Thats what I'm thinking as well. I got no heat but my resevoir coolant looks OK.
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Old 12-01-2008, 02:01 PM   #12
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If a little dousche kills the heater core, it was bound to leak and die anyway.
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Old 12-01-2008, 08:33 PM   #13
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Nice work! I need to do this too. This would be a good guide for the tech section...
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Old 12-02-2008, 04:41 AM   #14
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I knew that, thats what i'm looking to avoid
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Old 12-05-2008, 08:12 AM   #15
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i did that recently... didn't help my no heat problem
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Old 12-05-2008, 09:06 AM   #16
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Default Just did core using your instructions

Worked great. I used 3/4 inch tubing though and since it was cold outside I heated the hoses in the sink with hot water. They slid on perfectly and worked like a champ.

It was just only one blockage and it flowed right out. The car has 181K so I imagine it was really overdue.
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Old 12-05-2008, 09:22 AM   #17
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Nice job Tristan, adding to tech.
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Old 11-25-2009, 09:44 AM   #18
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Default Great pictures

I'm new here and a little bit of an newbie to fixing cars but when I started taking the hoses off the coolant began to rush out. Is this normal? If so what do you do to keep it from spilling all over the place?
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Old 11-25-2009, 10:43 AM   #19
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As recommended in the end of the tech article, I would bleed the system first by using the bleed screw at the front of the radiator on the driver's side and then do this. Your heater core holds about 24-36 oz of coolant and the rest is in the engine and the radiator. The water rushing out is typical because even though the car is cold, I hope, it is still under some pressure and its looking to get out either into the reservoir or the open hose. If you dont have heat after this, its probably your thermostat. I found that the easiest way to check this is by warming up your car, drive to the closest highway or high speed street where you can go abouve 50mph. If when you start getting on the highway you see that the temperature guage is lowering and when you are on the highway its still low but when you get off and stop for about 1-2 minutes it start to get up to the normal level, its most likely your thermostat. The water circulates faster through the system at higher speeds because the water pump is controled by the timing belt. If the thermostat is always open, water passes through the radiator to cool before it goes back into the cooling system. If the thermostat is closed, that means the water is below the 180 degrees and is keeping your engine cool. So, the thermostat should open when your car's water temp is above 180F and close when your car is cold. After the thermostat change you should see that the temperature stays the same on the local roads and the highway. Hope this helps. It a PITA to change the thermostat but well worth it. Good luck.
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Old 12-14-2009, 03:22 PM   #20
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