My son drives a 1998 Audi A6 Quattro that is doing something I cannot figure out. He can be driving the car and all of a sudden a roaring noise comes from under the hood. He can stop and shut the engine off, restart it and the sound goes away. For a little while. I looked and found a bolt missing from the A/c compressor mounting bracket. I also had the serpentine belt replaced at the same time. I thought it would cure it since the compressor was pretty loose. Tonight he took the car down to TCU, about 10 miles. After about two hours he called me and told me that the noise came back. He stopped it twice and shut the engine off and it stopped. He was heading for home and hit a dip in the road and the roar restarted but would not shut off when he restarted the engine. He called us at home and we went there to see if we could help. I looked at everything and saw the A/C bolts were tight and the belt was in good shape. I started the car and it made no sound . I drove it home and it ran perfectly. I cannot figure it out. Maybe the clutch is getting weak on the compressor, I just cannot figure it out. Any of you had anything like this happen to you???
Cracked airbox? Fan thermostat taking a dump? Hot or cold occurence? Seems electrical since a reboot helps. Vag-com it
Airbox is okay. It would seem electrical like you say except sometimes it will not reboot and the noise continues. I have to park the car and let it cool. It seems to do it as soon as the engine starts when cold, then reboot and be fine. If it does not do it when it is cold, it will do it after driving it for about 45 minutes to an hour. Then it will not reboot and has to cool off before it runs right. I believe it has something to do with the a/c compressor or a/c clutch............I guess I will end up taking it in. Usually I do as much as I can myself but this one has me baffled........
I would be thinking about the electric cooling fan and associated circuitry. Not sure about that particular model, but many of the German cars have 2-speed electric cooling fans, and the high speed typically doesn't kick in except under quite extreme conditions - but it often makes a LOT of noise when it does. Several possibilities - a wire has rubbed or been pinched, causing an intermittent short (hitting the bump changed the position?), a relay could be bad, the fan housing could be cracked, allowing the fan units to shift position, a fan blade could be cracked or broken, causing vibration under certain circumstances...you get the drift. If it's accessible, I would unplug the wiring harness going to the fan unit, completely disabling it, then drive the car (keeping an eye on the temperature gauge). If you keep moving, the car shouldn't overheat (unless it's really hot down there). If the problem doesn't occur under that circumstance,then you know the problem is somewhere within that unit. Good luck! Bob
My VW Corrado V6 had an auxiliary electric water pump that was supposed to keep the coolant circulating for a short time after the engine shut off. It went haywire and started coming on at random times, and it eventually started making a terrible noise, like the impellor was hitting on the case. I unplugged it. Possibly something similar on your Audi?
I have narrowed it down a little bit more. It sounds like it may be coming from the cooling fan clutch assembly. I started it this morning after sitting for three days. It idled for about 30 seconds then started making the noise. I was under the hood at the time so I was able to isolate the general area that it is coming from. I rotated the fan blade with the engine off and it seems to be a little sluggish possibly indicating the fan clutch could be going out. The noise stopped when I turned the a/c switch on. I stopped and restarted the engine several times and the noise has not repeated, with the a/c on or off. I have been around cars, general and race cars all my life but this is confusing to me........ Correct me if I am wrong but shouldn't the main cooling fan driven by the belt spin easily when the engine is off? It will spin about once when I give it a good spin with the engine off. I think the noise is from a drag on the clutch. Does this sound feasible. It has nothing to do with the auxiliary cooling fan located to the side of the main fan.
Noise has suddenly decided to go into hiding. I bought a new fan clutch and was going to attempt to put it on but am held up while trying to determine how to hold the shaft in place while turning the main nut to remove the fan. As soon as I bought the fan clutch it is like the thing has a mind of its own and decided it did not want me touching it......WEIRD....... So, to answer your question, no, no resolution yet.....I guess I could just take it to the shop but I am the kind who prefers doing most things myself if I can.
There's a special tool to hold the pulley so you can break the fan clutch loose...google "schley 63600" and you will find it. Once you see it and understand how it works, you may be able to improvise something. If you decide you want to buy it, the best price I saw is $53.99 at eToolDirect.com BTW, the fan clutch uses a temperature sensitive viscous coupling, so some resistance is normal, and it wouldn't necessarily spin freely - especially if the engine was warm when you were checking it. Good luck with it...
Thanks. I bought the fan/clutch at Autozone and they do rent tools but the two they had shown for this application are definitely too large. Another friend also told me there should be some resistance . We are going to take a look tomorrow and see if we can get the old one off. Putting the new one on looks to be relatively easy. But for me lately, nothing seems to come off "relatively easy"...
I had to work today so a friend took a look at the car. He removed the old fan clutch and replaced it with the one I had bought. He owned his own shop for over 20 years so my son said he made real quick work of it. He had the old one off, swapped the clutch on the fan blade and had it back on in under 30 minutes. We have put about 2 hours driving time on the car since it was replaced and there are no symptoms of a reoccurence,,,,,,,,yet. It looks as though we found the culprit and have it taken care of for under $100 including paying him for replacing it............
