2001 Audi Quattro 2.8, coolant has been slowly leaking on the passenger side when the car is parked overnight, no leaks while driving though. This morning went out and the all the coolant leaked out, again passenger side. Suggestions? My fan to my AC also stopped working at the same time.

First off, the bad news:
DO NOT DRIVE it while you have coolant missing/leaking. If your engine over heats (and it sounds like it already did if it shut off) you could crack the engine block, which means you'll be in for a HUGE thousands of dollars repair).

Secondly, the optimistic news:
It sounds to me like all you have is a broken radiator hose, which is probably less than a $20 part. Start by checking all the hoses, find the one that's broken/cracked or leaking and replace it.

Thirdly the less optimistic news:
You could have a bad radiator. If you're radiator is leaking you need to replace the radiator. Probably a few hundred dollars for a new part.

If it's none of the above then it could be leaking from around the water pump, head gasket, or some other part.

Fill your radiator back up with water (when the engine is cold) and look for leaks. If you see nothing, start it back up for (no more than a minute or two) and look for the leak. Once you've found the leak, flush the cooling system and fill it back up with the proper coolant (not just any coolant, get the right coolant for your car at the auto parts store or dealership, just ask them what you need- they can look it up). Be sure to use the proper procedure for returning coolant to the system (you need to fill it up wait for the thermostat to open, then add more coolant- missing the last step could cause your engine to over heat again, and crack the block. Never add coolant/water to a HOT engine (or you could crack the block).

If you find the leak, replace everything that's leaking, replace all the coolant, and find that you're still slowly losing coolant mysteriously (no drips anywhere) then you did indeed crack the block.

Good luck James. Let us know how it goes.

First of all, are you sure it is a coolant leak and not the natural draining of the Air Con., a leak on piping to or from the washers, condensation from the exhaust etc.?
Does the coolant level drop significantly and if so, how much and over what period?
Can you collect in a tray the liquid that is leaking? What does it look and smell like and what colour is it?
Does it leak with the air con disconnected?
Does the heater work properly?
When you say that it is leaking 'right under the middle', I presume you mean the middle of the car. If you park over a newspaper, where does the drip end up (which might not necessarily be immediately below the leak)?

Check your heater core. I had a 98 saturn that did the same thing and didnt realize what it was until my heater didnt seem to be as hot. Should be under the dash most likely toward passenger side. Look in a repair book to be sure.

You have air trapped in system , change thermostat , bleed air from system , let it run hot while adding coolant with blower full blast on all front and rear heaters .

Unfortunate you're losing coolant into the cylinders, where it's being burned off and exiting out the exhaust. When you initially added that cold coolant into the hot radiator, and hot engine (sit down) you likely cracked the engine block. Best case you just need to replace the head gasket.

do you know if they replaced the O ring rubber that connects the pipe under the intake Mark?
One of its trademarks is it only leaks after the vehicle sets overnight.

quick method is to park the car overnight, mark the wheel locations with chalk. after you have moved the car have a look at the pavement. that will give you an idea or what location the fluids are leaking from. if the water pump is failing it will start leaking water from a small "weep" hole on the front.
check your oil as well and let me know what colour it is as well as the colour of the exhaust smoke.

I have an A4 quattro 2003 and have the same problem. Found hose at the top end of engine at the back close to the battery housing was leaking. Terribly awkward job to replace , been quoted £200.

head gasket!