How bad of a sign is it when....
 

White smoke, smell of burnt coolant emanating from somewhere under the coolant reservoir? Coolant level is a very SLOW leak, have to add a bit of coolant from the dealer every 6 months or so.

The white smoke is coming from under the reservoir (engine side). I never notice anything on the garage floor and don't see anything dripping...

Still holding out hope that I won't need to get down to the manifold...but am I correct in realizing the longer I cannot find the leak the greater chance it is a manifold issue.

How many hours on a book level am I looking at for this type of leak?

Car is not overheating.

possibly a cracked coolant tank.

common failure point. it is one of those things that doesn't leak when the car is cold, but as it reaches temperature and the reservoir becomes pressurized starts a slow leak out the bottom seam. drips down on the manifold and bingo bango bongo, smoke.

first guess. cheap and easy to check/fix

report back

good luck

Could be the cap, or the reservoir, or the hose. The first is super simple. The second is 30 minute job, and the third is bit more involved. I doubt that it is head gasket issue if the car is running okay.

It would be helpful to know what motor you have.

If it is a 2.8 there are lots of potential water leak sources in that area.
There are hoses between the reservoir and cooling system, the reservoir, the oil cooler next to the oil filter, the hoses that connect to the oil cooler, etc. etc. etc.

Is it dangerous? -- Damn yes !!
The audi water temp gage is high in the system and it looses it's ability to tell you how hot the motor is getting once the level drops below it. (Don't ask how I know)
Since you don't see water on the garage floor the leak is near the hot motor and it is evaporating before the water gets to the ground.

OK - I'll tell you - I lost an Audi motor due to a leak just like the one you've described.
Added water/antifreeze - Couldn't find the leak -- Added water/antifreeze
- Couldn't find the leak -- Added water/antifreeze - Couldn't find the leak -- Added water/antifreeze - finally it blew the heater valve - fixed it -Added water/antifreeze - and then one day it lost all the water and I didn't catch it until the oil temp went up and then it was too late.
I suspect the real leak was at the back of the motor at the crossover pipe but was so pissed at Audi that I got a Mercury --

Ha. Well I owned a 1997 mercury cougar xr7 supercharged years ago...it was the biggest time/money pit I've ever been a part of...and thats saying something.

Mine is a 2.8. For 20 bucks and a bit of my time, its worth it to try the tank and see if thats the problem. Its very frustrating. I only see the smoke when I turn the car off, like a poster above said.

02A6Beau,

Probably a dumb question, but how do I remove the tank to inspect or replace without coolant going everywhere? Once I disconnect the hoses won't fluid come pouring out??!

you are going to lose some fluid. you can probably see that the expansion tank isn't too terribly "oversecured". Remove the screws that hold it down, and get some wiggle room. Then you can carefully clamp (read: vise grips, see also: carefully) the smaller rubber hoses to the expansion tank to minimize coolant loss. You can also try to use plugs in the ends of the hoses. Did I mention carefully? Either method requires some "risk". You can catch most of the coolant that is in the tank and will lose just a little from the hoses once you disconnect.

you also have the option to not do anything with the hoses once you remove them. you are going to lose coolant but not ALL of the coolant.

-not an expert, just an enthusiast

Add to that thought a bit... A plastic cup is your best friend. Make sure the system is fully cooled off. Unscrew 3 screws holding the expansion tank. Place a small plastic cup under the hose connection the the front of the tank. Undo the hose clamp and slide out the hose until the coolant seeps out. After about a couple of cup full, you can undo both hoses without dumping out the coolant.

BTW, I think the proper way of doing it is to unscrew to drain and drain out the fluid, but I am too lazy to jack the car up to crawl under it.

yeah?

When I did my timing service I did the "take the whole front of the car off" and I have yet to find the drain referenced in the Bentley....

or any other drain for that matter. ended up just pulling the lower hose. (that sounds dirty)

just sayin' ;)