Flushing Heater Core (B5 A4 ARGHHH)
 

The heat is very weak in my 2001 Audi A4 2.8 Quattro. I have read that this can be caused by a partial block in the heater core (I guess that this is a fairly common problem.) Many people flush the core with CLR. :eek:
I have tried running distilled water through it with a drill pump and I have used an air compressor with the regulator cranked down to a fairly low pressure. Nothing really came out. I was thinking about using some sort of detergent. Any recommendations?

Been there done that. CLR is the best thing to use. You need higher pressure.

Try pushing through it with a garden hose. Use the nozzle, to give it short quick blasts, then just flush through it in both directions till it flows good, and comes out clean.

Keep trying but when all else fails you may have to replace it.

It's a dash out job. I did mine in my VW Golf and it took two full days. Not fun.

I did the reverse garden hose through the core for 2 winters.

I end up replacing it the 3rd time.

What Fred said.

Garden hose and both directions.

Some cars, like my Tahoe, develop air pockets so they need to be "burped".

Park car on an incline or jack up the front, remove radiator cap and let the car run for a while.

Are you sure you're not getting good flow through the heater core? Pull the exit line and see how it's flowing at idle (obviously cold so you don't burn). Does the car have a heater valve? How's the water pump?

Always back flush. My landcruiser has two heater cores, be thankful.

I back flushed the heater core on my wife's Passat, B5. I used a clear hose for the exit hose and a standard black hose for the entry hose. I flushed in both directions and was able to see the crud come out of the clear hose. (it didn't look like much of anything was in there but evidently it was enough to lose heat.) Also I just used the spray nozzle on the garden hose and slow increased the pressure. I don't know how much psi was used but I didn't use full pressure.
I also recommend you replace the coolant in the entire system at the same time.

Thanks for the suggestions!

I generously gave Pelican and Sunset Audi a lot of my money this summer when I purchased all of the things to do my timing belt. In addition to this, I found that I had several metal coolant lines that were severely rusted (PITA to get to and change), and I found a bunch of other things that needed attention when I had this thing apart. I found this article which explains how the heater core works in these cars. I am sure that I have a little bit of flow, but I imagine that a lot of these little lines are clogged and a few are probably not.

I do not think there is an airpocket in the core. I bought an airlift system because this car has given me so much grief with the heat. I also bled it afterwards (near the heater core location) by running it for 5 minutes at 3k RPM. I know it is 100% filled.

I guess I will try an air compressor first (both ways), followed by a garden hose (both ways). If there is not a lot of crud coming out, I am thinking about using what GM recommended to get rid of their dexcool sludge (Oxalic Acid + Sodium Carbonate). Apparently it is safe for the cooling system and very effective.

Why not use CLR?

Redbaron - What coolant were you running in your A4? Was that the VW/Audi G12 or something else? (I have not seen a sludge issue when running G12.)

The heater core sludges up even when using G12.

some pros use a water line which has the air compressor hooked up to it. short bursts of(regulated) air with the water.
usually back flushed.

I did the following things...

Mixed Oxacilic acid into boiling hot water and poured it into the heater core
Mixed Sodium Carbonate into boiling hot water and poured it into the heater core
Used a garden hose to flush the heater core out
Used an air compressor to blow out the tap water

I then filled the system with a 60/40 mixture of fresh g12 and bled it thoroughly. The result was very hot heat!

When I got the car two years ago, the previous owner was NOT running G12. I decided to dump whatever he was running and I ran the car with distilled water for a short period; I then purged that and I poured in a fresh mixture of G12/Distilled water.

I was afraid of putting CLR in because it says to not use it with any brass/copper.

Thanks for the help!