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No heat at idle after some soft of coolant flush/drain/change/treatment? Here is fix

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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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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 01-03-2010, 12:58 PM   #11
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I just started replacing my core yesterday. I did flush several times over the past year or two, but now I can smell coolant when running heat and the windows get foggy very easily, both signs of a bad core. So, I said what the hell. Turns out, it's not very difficult at all to disassemble the entire dash, but it does take time. If you have a little confidence and aren't afraid, it's not so bad.

I'm waiting for the new core for ECS tuning, then putting it back together may be a different story.
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Old 01-03-2010, 01:48 PM   #12
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BTDT...well, I did the AC evaporator anyway. Too bad about your core; they are usually a low failure item.

Agreed about the difficulty. Lots of parts, but not really a terrible job. Following Bentley makes it much easier.
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Old 01-03-2010, 05:42 PM   #13
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Quote:
Originally Posted by 4Driver4 View Post
I use compressed air to bleed the system with the car off and the engine cold. Works great.
can you detail how you did this? I'm about to try this to try and fix my heat issue
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Old 01-04-2010, 05:42 AM   #14
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Quote:
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can you detail how you did this? I'm about to try this to try and fix my heat issue
Realistically, no. Providing a detailed write up would take me about 4 days to write. But, I will work with you as you are doing it. Definately use a manual. I used the Haynes, but I'm sure Bentley would have been better. Everyone says do t do it, but I think that's just the hype. Most people probably haven't actually dine it themselves. If you feel like tackeling it, go for it. It will save you over $1K.

Here are some things you'll need:
1. A warm garage that provides room on each side of car.
2. A shop to discharge your AC
3. New coolant to fill when your done
4. For tools, you'll need a ratchet set, Allen set, triple square set (or whatever it's called)
5. Patience
6. Plan for a good three to four days without your car.

Enjoy it!
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Old 01-08-2010, 05:17 PM   #15
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Quote:
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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.
how did you do this exactly, as far as pushing coolant through with compressed air.
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Old 03-04-2010, 10:08 AM   #16
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Hi - I just bought a 2002 allroad and the heat worked when I test drove it. Yesterday when I was trying out the heat to see how it worked, it was blowing only cold air. I have the heat setting all the way up to high and the car was idle for 20 minutes.

I then shut the car off and let it sit for about 40 minutes, then started it up and it blew heat for the forst 30 seconds, then cold again. Does this sound like the air pocket issue above? The coolant was replaced when the car was services just before I bough it.

Also, do you happen to still have the photo mentioned above showing the bleeded line? I think I will try bleeding the line first.

Thanks!
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Old 03-04-2010, 10:48 AM   #17
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The core is not properly bled. I'd take it back to whoever serviced it and have that fixed. Check the Tech Section for information on bleeding the system.
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1983 Mazda RX-7 (revolutionary sports car)
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Old 02-24-2011, 12:06 PM   #18
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Default How to pressurize?

Quote:
Originally Posted by 4Driver4 View Post
I use compressed air to bleed the system with the car off and the engine cold. Works great.
How did you go about putting pressure on the system?
I've tried bleeding it but the -24 C temperature makes it a bit difficult to do this properly outside with the car running.
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Old 12-17-2011, 02:19 PM   #19
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how do i preasurize system to get air out and get heat at idle ? please help
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Old 12-17-2011, 04:02 PM   #20
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Default Start a new post about your problem...........

Quote:
Originally Posted by tboyd1971 View Post
how do i preasurize system to get air out and get heat at idle ? please help
........instead of reply to a really old thread first.
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