I had a problem with my 2003 S4 losing coolant and no obvious deposits on the floor.
It turned out that the "crimp" clips on the radiator had pierced the very fine tubing on the outermost part of the main radiator and created a very small leak that would evapourate very quickly when hot and just dissapate when cold.
Check the tubing around the "crimping" on the front panel of the radiator and the very front of the car.
This turned out to be a warranty job... good luck.
It turned out that the "crimp" clips on the radiator had pierced the very fine tubing on the outermost part of the main radiator and created a very small leak that would evapourate very quickly when hot and just dissapate when cold.
Check the tubing around the "crimping" on the front panel of the radiator and the very front of the car.
This turned out to be a warranty job... good luck.
