B5 S4 heater core clogged

jlagnese at massed.net jlagnese at massed.net
Wed Jan 1 19:51:23 PST 2014

Happy ending!
----- Original Message -----
From: Ti Kan <ti at amb.org>
To: quattro at audifans.com, biturbos4 at audifans.com
Sent: Tue, 31 Dec 2013 18:17:17 -0500 (EST)
Subject: Re: B5 S4 heater core clogged

Thanks to everyone who chimed in on this subject, I went ahead
with flushing the heater core with success today. The steps
I used were basically taken from these sites:


Upon taking the hoses off the heater core, I found that the
plastic barbs that the hoses attach to were broken and in pieces.
I was very careful in taking those hoses off, so I don't think
I broken them. These hoses were recently replaced by a shop, so
they may have broken the barbs. The broken pieces had severely
restricted the coolant flow through the heater core, and is
probably the primary cause of not getting much heat. I removed
all the broken pieces from the end of the hoses and on the barbs.

Fortunately, there is enough good barb left for me to attach the
hoses securely without leak. Otherwise the heater core would have
to be replaced and that's a big job that no one wants to do.

The only exception to the procedure outlined in the above link
is that I did the reverse flush only, not the forward flush.
I didn't want to risk damaging the barbs further by repeatedly
connecting and disconnecting hoses. The utility hoses I used
to do the flush were curved, heavy and unwieldy, and puts strain
on the barbs.

Anyway, the flush did produce a lot of brown sludgy junk, which
probably also contributed to the lack of heat. I ran water
through the heater core until the water came out clear. No cleaning
agents were used.

And voila! The heater now blows hot air through the vents. 
It was a cheap and easy fix, but I am a little annoyed by
the broken barbs. I can't really prove that it was caused
by the shop. Hope the heater core holds up. So far, so good.


> > On 12/26/2013 12:03 PM, Ti Kan wrote:
> The heater core on my 2001 S4 appears to be clogged, there is
> very little heat out of any vent even with the engine fully hot
> and the climate control temp set to HI. The blower is working
> properly, all air flaps seem to work too.
> Replacing the heater core is a BIG job on this car, involving
> the removal of the center console, entire dashboard, and many
> things beneath it. I don't have the time or the confidence
> that I could do this myself, and paying a shop to do it will
> be serious $$$.
> I read that a heater core can often be un-clogged by backflushing
> with either compressed air or water. My mechanic is reserved
> about this method, saying that there is high chance that it
> would cause the heater core to spring a leak into the cabin,
> which would _force_ a replacement of the heater core.
> What is your opinion about this? Should I try to backflush it?
> If so which is better, compressed air or water? Just how sturdy
> are these heater cores? According to the family album the same
> heater core is used on all B3, B4 and B5 Audis as well as the
> B5 Passat.

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