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A6 / S6 (C5 Platform) Discussion Discussion forum for the C5 Audi A6 and S6 produced from 1998-2004

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Old 01-17-2009, 07:59 PM   #1
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Default No heat at idle after some soft of coolant flush/drain/change/treatment? Here is fix

If you have tried everything, bled the system 2-3 times using the bleed valve located at the bottom of the engine, and are extremely frustrated and want to replace the heater core.. dont do it, its just a finnicky heater core air pocket.

The heater core generally only gets pressure when the car is revved up, because it is a passive system (i think), if there is any sort of air pocket, it wont leave through the hose for some reason, and needs to be bled properly.


There are two coolant hoses on the firewall directly next to the battery for the heater core.





The right hose(outlet) has a bleed hole on it. The hose needs to be pulled part way out, until the bleed hole is exposed.. you can see the tiny hole in the pic, ignore the numbers i borrowed this pic

Once the hose is pulled out to the point of the little hole being exposed to coolant, rev the engine up to 3-4k for 3-5 minutes. There will be coolant loss, and YOU ARE NOT DONE at the first sign of coolant through the little hole.. Keep going. For a while. And have someone push the hose in while the engine is still revved up after 3-5 min. (be careful here, as it can be HOTTT).

IF THIS DOES NOT FIX YOUR PROBLEM, REPEAT.

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Old 01-18-2009, 05:40 AM   #2
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Default the factory procedure calls for an extension tube to be threaded into the reservoir opening....

...because the level of coolant in the reservoir must be higher than the bleed hole in the heater hose to bleed the system effectively.

I don't have the factory tool (VAG1274/8 and VAG1274/10) so I gently pressurize the reservoir and then slip the hose back over the bleed hole once a steady stream of coolant is coming out.
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Old 01-18-2009, 07:53 AM   #3
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Default Re: the factory procedure calls for an extension tube to be threaded into the reservoir opening....

Yeah i know.. but my way will work.. I just see a hand full of people running around with no heat at idle, and cant figure out why. Plus, there is no definitive guide when i searched.. so this is enough for someone to get heat at idle!
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Old 12-22-2009, 05:16 PM   #4
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Do you think that an air pocket could also prevent coolant flow to the feed hose for the heater core? I am working on a 101,000 mile 2001 A6 Avant 2.8l V6 30V ATQ that has no flow to or from the heater core. With both heater supply and return hoses disconnected from the the heater core pipes in the engine compartment there is no coolant flow whatsoever in the heater core feed hose with the engine running at idle and warmed up. This A6 just had a timing belt, water pump and thermostat replacement. With air pressure applied to the heater core and supply and feed hoses in both directions there is flow and no indication of a blockage and the G12+ coolant is very clean. The engine does not overheat at idle and the I/P gauge is reading normal at straight up midrange. There is some return coolant flow visible in the small diameter hose leading to the coolant reservoir. This is my friend's shop that deals primarily with BMWs so their Audi repair experience is limited.
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Old 12-23-2009, 04:14 AM   #5
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I use compressed air to bleed the system with the car off and the engine cold. Works great.
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Old 12-23-2009, 10:37 AM   #6
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Thank you. We did the same thing . Works great now. With the C5 A6 the heater core is very low behind the I/P
so the coolant has a hard time to flow to the core at idle speeds making for large air pockets.
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Old 12-23-2009, 11:51 AM   #7
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Bleed it.
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2005 A6 Sedan Q 3.2 (wife's whip)
2000 A4 Avant Q 2.8 (daily driver)
1980 VW Scirocco (mid-life crisis car)
1983 Mazda RX-7 (revolutionary sports car)
2003 Mini Cooper S (just because)
1995 Mazda Miata, Superdupercharged(anti-Audi)
1999 Mazda Miata SSB (track beotch, no plate)
2003 GMC Yukon Denali XL (the anti-earth)
2004 Dodge Dakota (hey, at least it's stick and 4x4)
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Old 12-23-2009, 06:58 PM   #8
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Finished. Pushed coolant through the heater core with compressed air. Note the above there was no flow to the heater core feed line initially with the feed line disconnected and the engine running.
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Old 12-26-2009, 09:51 AM   #9
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Sounds like you had a clogged core and air in the system.

Make sure you bleed the core as 4driver4 stated using the bleeder hole on the outlet hose.
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Old 12-26-2009, 12:25 PM   #10
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No, the core was very clean. The problem was no coolant to the core with both heater core feed and return hoses disconnected. The heat is on full blast now.
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Old 12-26-2009, 12:25 PM
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1998, a6, air, audi, bleed, cold, core, heat, heater, idle, idling, jeep, pocket, v6, vw


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