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gomi_otaku
gomi_otaku, Technician
Category: Audi
Satisfied Customers: 3428
Experience:  VW certified technician, Chicago VW/Audi Training Center, Seattle VW/Audi Academy
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Doc. I never did restore that 2005 A4 Cab. Decided it was

Customer Question

Hi again, Doc. I never did restore that 2005 A4 Cab. Decided it was just too much money and time for the value of it. I can see why insurance is so high on these! Have a new (too me) 2001 A4 Quattro with about 30k miles. Need some help with the heater, and I know you can help. Thanks, Doug
Submitted: 1 year ago.
Category: Audi
Expert:  gomi_otaku replied 1 year ago.

The best way to bleed the heater core (since it sits higher than the reservoir opening) is to either drive the car up on a ramp slightly, or just run it to temp first. Loosen the clamp on the heater hose that has the weep port, but do not pull the hose back yet. Warm it up to temp, and while running, slightly slide or angle the hose until coolant streams out. You want it at temp so it will have good pressure. There should be air built up there as that is where it accumulates. So it may spit and sputter, but as soon as you get an actual "stream" of coolant, close the hose again. You'll need to let the car cool down again overnght, and then warm it up and do it again to see if you get any more air.

Just note that since the heater core is low, it will tend to attract "gunk". I have taken both hoses off and alternated with bursts of water and bursts of pressureized air (using a long flexible plastic wand to get the air down into the bottom is best) and you will see particles of rust flake, etc. I try to put a rag over it as best possible each time I blast with the air. Eventually when you don't feel the particles hitting your rag anymore flush through with clean water, put one hose on, fill it with water, and put the other hose on, this will help it get flow through with less air to purge

Customer: replied 1 year ago.
Good morning. Thanks for the suggestion. I have done the part of the procedure where the engine is thoroughly warmed up, then the bleed port at the fire wall is opened and bubbles come out. Though the engine was only idling, a weak stream of coolant did eventually stream out, so I closed the clamp again. Maybe I need to have someone rev the engine while the port is open to get a better flow.Also, since the car has less than 30k miles on it, even though it is a 2001, I certainly would not expect it to have much gunk in the heater core. The coolant reservoir looks very clean in the bottom, and the coolant is clear. But I will try the entire procedure this weekend and report back to you. Thanks.Doug
Expert:  gomi_otaku replied 1 year ago.

OK- as long as the flow switches from bubbles or air, to constant coolant flow, that's what you want. Having the system closed so it builds up a lot of pressure as it heats up is best, ***** ***** you open that port it really spits all the air out. If you can incline the car at all, say by driving it up on a set of car ramps in the front, that would help by lowering the heater core relative to the coolant reservoir.

Customer: replied 1 year ago.
Hello again. I did as you had suggested in bleeding the air from the heater core, including disconnecting it and blowing air through it just in case any 'gunk' had accumulated in it. No discernible amount of gunk came out, and the flow through it seemed to be very free. I then reconnected it, filled it, bled it again and there was no improvement.This morning it was 39 outside, so it was a good test situation. I drove the car to work, over an hour commute at generally cruising speeds of 45 to 80. The climate control was set to "Auto". Even after the coolant temp gauge was up to normal, the air coming through the vents was barely lukewarm with the temp set at 75 deg. I adjusted it up to a setting of "Hi", and it still did not get any warmer. Note that the fan speed did not increase to max, either - was only about 2/3 of the fan speed range. None of this seems to be as it should be, based on my experience with a 1997 A6 with 280,000 miles on it. When its climate control was set similarly the air coming out of the events was HOT. Suggestions? Thanks. Doug
Expert:  gomi_otaku replied 1 year ago.

When the car is up to temp, feel the hoses running into the heater core in the engine bay, make sure they are hot. It's always possible you have a bad coolant pump, this era was notorious for the impeller cracking and slipping on the shaft.

Customer: replied 1 year ago.
Hi. OK, I will check that. I know they are hot after it has been running for a half hour or more, though I'm not sure how hot they should be. I have an IR temp reader, so I will check tonight and let you know the temp of each of them after I get home. This is a little more than an hour of driving.Are you referring to the water pump driven by the timing belt, or does this model have a supplemental coolant pump? If so, where is it located? Thanks.Doug
Expert:  gomi_otaku replied 1 year ago.

what engine do you have in this?

Customer: replied 1 year ago.
Hi. I have the 2.8.
Customer: replied 1 year ago.
Good morning. You never replied after I answered what engine I have, so I don't know where you were going with that. Anyway, I was able to measure the temperatures of the heater core inlet and outlet HOSES, so the coolant temps inside the hoses are certainly a little higher. The hose temps are 134 for the inlet and 77 for the outlet, after the engine was thoroughly warmed, was revved for a couple of minutes, and then sat at idle while I measured the temps. To me this seems quite low, as would think the inlet temp should be closer to 200, even on the hose. Isn't this coolant coming from the engine block directly? Where is the coolant pump you referred to before, and how does that work into this system? Thanks. Doug
Expert:  gomi_otaku replied 1 year ago.

There is a secondary water pump, often coolant will migrate into the electrical connector and knock it out. I'm wondering if it is impeding your flow.

Customer: replied 1 year ago.
Hi. OK, sounds reasonable. So where is the pump located on this engine?
Customer: replied 1 year ago.
Good morning. Still waiting for an answer to my last question.
Expert:  gomi_otaku replied 1 year ago.

Sorry, busy weekend!

The secondary coolant pump is accessible from underneath the car- it is behind the alternator, just follow the coolant hoses to it.

Customer: replied 1 year ago.
Hi. OK, thanks. I'll try to check that out tonight and let you know what I find out. Does it run whenever the engine is running, or just when should I be able to confirm its operation?
Expert:  gomi_otaku replied 1 year ago.

It should run for sure after you shut the car down hot, as part of it's function is as an after-run pump to help cool the car down without hot spots.

Customer: replied 1 year ago.
Hi. Now I'm confused. All the references I see for this pump is as an "after-run" coolant pump, with no reference at all to it as a "secondary" coolant pump. The only references to it are NOT as any sort of 'extra' coolant circulation pump, just after run to cool down the engine evenly when shut off.
Expert:  gomi_otaku replied 1 year ago.

Unless you have some other kind of obstruction in the system preventing flow, I can't see what else it could be. If you flushed out the core, don't see any gunk in the system, and are able to purge the air out of the bleed port until fluid runs out, then the only other thing that could be is some kind of obstruction in the lines. You said the hoses to the heater core were not getting hot.

Customer: replied 1 year ago.
Please, you didn't answer my last question! When does this pump run, just for 3 minutes after the engine is shut down, or constantly AND for 3 minutes after the engine is shut down?Also, just to be clear, the heater hoses are not getting as warm/hot as I would think they should, but the rubber inlet hose is at 134 deg. Should it be much hotter?And, though I was not able to remove the sound panel and crawl under the car last night to check the pump, I listened very carefully right after I shut off the engine when I got home late last night, but could not hear anything at all running in the front right corner. I live out in the country where it is very quiet, too. Should I have been able to hear it run?What about possible control problems? As I said much earlier, the fan never runs at full speed, even when the outside temperature and the climate control setting are 50 deg apart? Can this be a part of the problem?What if the 'mixing door' is not moving all the way as it should? Can this be part of the cause?Please address each of these questions. Thanks.
Customer: replied 1 year ago.
Please, you didn't answer my last question! When does this pump run, just for 3 minutes after the engine is shut down, or constantly AND for 3 minutes after the engine is shut down?Also, just to be clear, the heater hoses are not getting as warm/hot as I would think they should, but the rubber inlet hose is at 134 deg. Should it be much hotter?And, though I was not able to remove the sound panel and crawl under the car last night to check the pump, I listened very carefully right after I shut off the engine when I got home late last night, but could not hear anything at all running in the front right corner. I live out in the country where it is very quiet, too. Should I have been able to hear it run?What about possible control problems? As I said much earlier, the fan never runs at full speed, even when the outside temperature and the climate control setting are 50 deg apart? Can this be a part of the problem?What if the 'mixing door' is not moving all the way as it should? Can this be part of the cause?Please address each of these questions. Thanks.
Expert:  gomi_otaku replied 1 year ago.

I never addressed the possibility that your temp flap may not be making a full swee, because it seemed that the hoses were not getting up to full temp. NOrmal operating temperature is 175-195 for the engine, and that should come through the heater core at the same temperature. So I have been going on the assumption that you are not getting full flow in the system, for whatever reason.

As far as I know, the after-run pump is just that- activated only by the system to run after the fact- but I could be wrong, for whatever reason this is not clear in any of the literature. If you had a VAG-COM software or scan tool, you could run output diagnostics to see if it runs at all. The only way to be sure is to be able to feel or hear it run.

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