iwonder1

I have this very same problem with my 2004 A$ Quattro 1.8T. I have NO heat unless at least 2000 rpms then it blows half way decent. BUT as soon as you slow down or come to a stop right back to cold. I've had the heater core tested for leaks power flushed. Thermostat and sensor witch was leaking as well as the rear flange on the back side of the head. Also had a plug removed from the "Bleeder" line so I could purge the system. Haven't tried that yet a second maybe I didn't get it all or do it right originally. I was loosing about a quart a month or 2 so leaks were hard to find until belly pan was dropped then we could see the problem. Since the leaks were fixed "supposedly" very minimal coolant loss like a pint to a quart every 6-8 months which I think may be normal due to evaporation. The caps on the resistors are NOT air tight. Where and what is the

Anyhow, here's another question. What's the deal with the head gasket I keep reading about? How can you tell if it's bad? My car NEVER goes above mid way between C and H on temp gauge with is normal operating temp. The car runs great and has NEVER over heated once. Any comments or suggestions would be appreciated?

Lastly I have a constant "BUZZING noise which seems top be coming from the trunk area. I think the fuel pump is located in the tank right underneath. Funny thing is it only starts to do it when outside temps drop. Then in spring and summer cone it stops. Never had any trouble with the cart so obviously the pump is working. My question is ths: "Is there a relay or solenoid that starts the pump that may be sticking in the cold weather? OR maybe I'm totally off track here. Any other suggestions what it could be?

One last thing i've not heard of that could be a potential problem. What is this part and is it factory?




Thanks to all who reply in advance

Prospeeder

With your heat, I dont care if its been flushed or tested blah blah its bad and needs replaced search and you will see.

As with your noise, theres a bulletin about the noisy fuel pump. Audi says replace the fuel filter, if that doesnt fix it the pump is worn out and making noise and must be replaced.

And No its not normal or evaporation to have coolant disappear ever. Its a totally closed system theres no way it can evaporate. You have a very very slow leak which will eventually show itself.

iwonder1

Thanks for the input. I really appreciate that. I will definitely get a new fuel filter and hope that's an easy fix. I just have a question about your comment "With your heat, I dont care if its been flushed or tested blah blah its bad and needs replaced search and you will see. " What needs replaced, and what do I search for? Where? What will I see? There are only so many parts to a cars heating system. Please explain. As far as it being a completely closed system how does the coolant get to and from the engine? The reservoir right? Which does not have a sealed cap on it.So some evaporation will occur. Will it not. Please explain.
Thanks

Prospeeder

How is the reservoir cap not sealed? The system pressureizes to 16lbs when hot. If it wasnt sealed how could it build pressure? ALL cooling systems are sealed system. If your thinking of the little open expansion tanks on like early american cars and Japanese cars its not the same system and they are still sealed just the expansion tank is not. If your tank cap does not seal the system then you need a new cap.

And search the forums on A4's with bad heater cores. They cannot be flushed, they will seem to flow fine and do not keep warm up or do the cold at idle warm revved up. The core is bad, they all go bad eventually, just a bad design for long term.

lyleswk

Prospeeder is correct in all he says, but you seem to be all over the place. Let me summarize and see if you are on the same page:

1) I don't think you have the same issue as the OP. He is losing coolant quickly; you have no heat (see 2 below). It is likely your heater core as Prospeeder says and I had no luck back flushing it. Just replace it.
2) As far as losing coolant and evaporation, again agree with Prospeeder. The system has to be air tight and it does not evaporate. I suspect after the leaks, the system was not completely full. It usually takes a couple topoffs after you run the vehicle after the system has been emptied completely. If this continues beyond a couple tops offs, you probably have another leak.
3) I wouldn't jump to a head gasket problem. But to answer your question, the head gasket is the item that seals the top part of the engine (the "head") with the bottom part of the engine (the "block"). If it is leaking, you get coolant into the cylinders and / or exahust gasses into the coolant. If bad enough (and it will eventually get there), the car will simply run poorly or not run at all.
4) As prospeeder said, the buzzing is likely the fuel pump. Start with the filter and if the noise is still there, you waited too long and trashed your pump.