Coolant...???
 

I added a litter of coolant on Sunday..I had to add another litter today..I does see any coolant
under the car..Is this serious engine damage..I have 150 k KM's on My 98.50 2.80..

Hold a foil pie pan against your exhaust pipe and see if water condenses....
 

If you are losing that much coolant into the engine somehow you would definitely have steam at the tail pipe.

You would have steam at the tailpipe anyway...water is a byproduct of combustion.
 

I would suggest dropping the belly pan and looking around. With the older green coolant, you would see a white crusty residue where the coolant was leaking. Not sure what color the residue will be with the Audi long life coolant, but with 1 liter missing so soon, you'll see something. A bad water pump, leaking radiator hose/radiator...can leak coolant.

Next I would check the interior of the car (carpets). A leaky heater core will usually leak coolant into the car. Sometimes you'll smell the coolant through the AC system.

Lastly, change your oil, and check the oil for coolant. If you find coolant in the oil, that's bad news. Time for a trip to the dealer...most likely a costly repair.

Oh yeah....wait till your engine warms up first. All cars condense when cold.

Check for steam in the engine compartment.

RKA is correct