jseklund

Hi all. I just finished up a second time doing my timing belt and also doing my tranny fluid for the third time on my car. After my first attempt at the timing belt on this car, I began noticing that I had no heat at idle during the winter. I was hoping to get that fixed this time around, and I have been trying everything.

First, I filled the system by just filling the resevoir and running the car, etc. I pulled back the upper hose on the heater core, then cracked the screw on the coolant pipe between the heads, and the screw by the throttle body is stripped so I am waiting on a new one from Audi.

That didn't work, so I topped up and removed the hose at the back of the coolant resevoir, set my air compressor as low as it would go and still blow air, and blew air into the resevoir to pressurize it. Coolant came out of the hose and into the bucked and also came shooting out of the hose coming off the heater core that I left cracked.

That didn't work.

So, I pulled apart the heater core and reverse flushed it, flushed it going forward, filled it with CLR, let it sit foor about 90 minutes with CLR in the core, and then did the flush both ways again. Everything that came out was crystal clear by the end (I did get some gunk out) and I seemed to get full flow through the hoses that I attached. There was so little resistance through the core that I could blow, with my mouth, through one hose and move all of the water out of the core...which isn't a lot of pressure at all.

Once this was done, I reattached the bottom hose, and then used a funel to pour coolant into the top pipe until no more would go in, I would blow on it (again, not compressed air...just blowing into the hose), and it would go in, and then I'd refill and repeat until blowing on it caused the coolant to come back out of the top pipe and into the hose. I then reconnected everything and started the car up.

After this, the coolant definately was flowing different. It was bubbling out of the bleader hole and had plenty of air coming out, where as before it was shooting out even though it had NO flow if I pulled the hose off entirely. The top pipe gets hot, then gets cold, then gets hot, etc.

While I seem to have slightly better heat at idle - it is still not hot. I now it is strange to be working on this in the summer, but I just wanna get it fixed.

Any thoughts on what it could be? Could it just need more time being bled? I still don't really have heat at idle...but it gets plenty hot under throttle.

Airbag

Well i dont have good news but i can say i feel your pain . I have been working on cars for over 30 years and this was the only problem to ever stump me.
It was on my 95 Audi 90 and had your symptoms exactly. no heat at idle .. at speed there would be enough to fry you but at idel in Februarly at 20 below you would die in your car if you got stuck at stop and go traffic.

I even replaced my heater core and that was a huge job . I was terrified of having it happen on my A6 but fortunately it didnt when i did that car ..

i can give some things that i tried that might give you some ideas ..

1. replaced heater core
2. replaced thermostat twice and water pump twice.
3. replaced heater hoses.
4. jacked the front end off the ground and tried pressure burp as you have

( my car did it for 8 years so i cant see this being the cause though. )

5. Replaced reservoir tank and cap.


The only thing i really established is that it was not a heat issue. but rather a flow issue .. i could take the heater core line off at idle and nothing would move through the core that is why i had no heat .. accelerate a litle and it would fly out .. That is even with the brand new core . some how it was bypassing the core. i temporarily put a piece of clear tubing on with soem fittings so i could watch the flow and sure enough it always stopped while at idle. Allmost like i needed a smaller pulley on the water pump so it would spin faster ..

the only thing left was the heater pipe that ran under the intake manifold on that car was maybe blocked but i gave up at that point as it wasnt worth the dollars involved in tearing the manifold off and the associated costs. i demoted it to a summer car and it was a great one .. then sold it to some kid.

The only thing i didnt do was replace the rad as i just couldnt see this being the issue .. but you never know ..

BTW it had the problem since i owned the car and the PO said Audi couldnt fix it either .. they just kept taking his money and trying things .. so he gave up and sold it to me

jseklund

Thanks Airbag. At the very least I can say this - I fully expected people to say that the heater core must be bad right away...and that I am crazy So there is some good news there. I can't see this being a heater core issue when I get full flow just blowing through the hose with my mouth. I can get some pressure going, I'm a big guy, but not that much. I didn't even have to seal my mouth to the hose and the water was flowing through.

What may have been a clue, in my mind, is that when I reconnected the bottom hose and then tried filling by funneling through a hose to the top section of the heater core...I poured in a good amount more coolant than I expected. I wonder if there was an air lock in the system before the heater core, and by filling from the top down, I got some of the air out..but this is a wild guess. I would pour it in, the fluid would be get to the point where it was in the hose and would stop going into the pipe, I'd blow into the hose and the fluid was gone...repeat, repeat again, etc. a few times before I couldn't get any more into the core....

Today, I was sitting in heavy traffic and kicked the heat all the way up while I was idling, and it actually felt warm hot...so I don't know. I'm gonna let the car cool down and try it again. Maybe it is fixed...but I don't have high hopes...

Thanks again!

Prospeeder

i see this ALL the time every winter. Its the core, you can flush and flush and flush all you want. But the way its designed, it just goes down a few tubes and right out. If you cut one open, they are filled with what looks like twisted pasta in each tube, to slow water down and conduct more heat. Well, they assist in allowing debris to pack into the core. So you may think it flows freeley, but thats the 2-3 tubes that your blowing through, not the whole core.

In your mind your seeing it like its one tube from start to finish, really its a whole bunch of tubes running parallel into end tanks. Reason for revving up and getting heat, the flow to the core is a bypass, so its not full on heater core flow, its just a trickle really, they want the water to go through the core slowly so it absorbs more heat and you get a hotter heater. More water speed makes more water go through the core, and the portion of the core thats actually working is able to supply you with heat, and a few of the partially clogged tubes may fill up and assist. But at idle, flow goes very slow and bye bye heat.

Tik-Tok

Oh man, I don't like the sounds of this thread, lol. I came in hear looking for an answer myself.

I just finished replacing my A/C pump (and drier), and I had the front clip off (just like doing the timing belt), now I'm not getting any heat at idle either.

Now I'm scared a mouse crawled into the system while it was open, lol.

jseklund

Just updating - so, after flushing a bunch and refilling...things seem to be working a little better, but I'm not 100% sure that the system is like it should be.

At idle, I now get warm air, but not super hot. When the car is revved, it gets red hot air coming out the vents. I went to feel the upper tube today and my hand stayed on the tube for just long enough for my burn reflex to pull me back it was so hot....so that is a much better sign.

Funny thing is, I didn't notice the no heat at idle until shortly after I did my timing belt the first time. When I did the flush, I got some gunk out, but nothing shocking (I have 240,000 on the car almost).

I have a feeling I had an airlock between the engine and the core, and when I funneled the fluid in and used my mouth to blow it in further, I got the air out that way....but it's just a theory. Use a towel on the hose if you use your mouth and be careful about anything coming back! I don't recommend it, but I did it....lol

Prospeeder

I dont get why you wont accept the core is bad lol. Read my posts. Just because your flushing and it has flow it means NOTHING! i have been through the same exact thing you are dozens of times, flushing, flushing, bleeding bleeding. Install new core, dont have to bleed or do anything, just immediate hot heat.

Airbag

Because soemtimes the core is NOT bad. I replaced mine and the problem continued. But if everything was fine, you did your timing belt or water pump and now you have no heat you have trapped an air bubble.

To the OP a little bit better is not fixed . mine always felt like id fixed it in the summer , but as soon as November hit i new it wasnt fixed.

Prospeeder

From experience working on hundreds and hundreds of these cars, if you have drivin it more than 5 miles and gotten some high rpms going, theres no air in system. You put a core in and the same issues? The Auxiliary water pump does work right? I find the bleeding procedure, drawn out and completely unnecessary. A quick drive and some rpms and it will burp it all right out, standing holding the hose open and revving and waiting and trying to bleed is a big waste of time. Just drive it.

jseklund

Prospeeder - I am not totally refusing to believe the core is bad. Actually, it is a fear of mine...a lot of work and money. And I know you have done far more work on these cars than I have, so I respect that and your opinion. I also know that your assessment seems to be spot on - I did my mom's timing belt on her 01 A6 and never bled it at all and her heat works like a champ.

Having said that, I do find it strange that I did the timing belt 18 months ago and have now gone through 2 winters without heat at idle. I don't have a lot of idling to do in the winter, so it hasn't been unbearable, and quite frankly, it still gets quite warm under RPM, so I'm not sure I would even go through the work to put a new core in even if I got the core for free....

Also, I have been thinking about your description of the core, and it makes a lot of sense - I've been blowing through a short section. What doesn't make sense is that, before I removed both hoses, flushed and CLR'd, and then refilled by funeling fluid backwards and blowing it through the system backwards, I had no flow. If I could get flow through the short section by blowing through, and the other chambers were plugged, then the pump should be able to create just as much flow through that short section and I would have had fluid coming out the top pipe, right? Or am I missing something?

As it stood, I could have pulled the hose off the top pipe and I would have lost a couple of teaspoons of fluid tops as it dribbled out at idle. Even under throttle I didn't get any flow through that pipe. I haven't pulled the hose again, but it seems like I'm getting flow at idle now.

I also get airbag's comments - but combined with Prospeeder's advice of drive the car and let it burp, my heat may be back. I will check it again over the next couple days. It is definately warm again at idle, after it has warmed up, I just want to be sure it gets warm at idle if I start the car.

Airbag, if you have some fluid kicking around, would you try what I did? Grab a section of hose and a funnel and disconnect the top tube from the heater core. Then funnel some fluid directly into the heater core, use a little air pressure...either from an air compressor set to 5-10 PSI or by just using your mouth to blow through (obviously be careful if you do this). When I did this, the fluid stopped going into the core and I could see it in the clear hose, then I pressurized and the fluid went into the core and I could fill it more until it came up to the hose, pressurized, filled more, pressurized, etc. It took a lot more fluid than I expected. I really believe there is an air lock somewhere between the engine and the core. I have seen quite a few threads on this, and I think Prospeeder may be right on at least 90% of these - but maybe in some cases something else goes wrong?? If you try this method, maybe we can solve something for others?