S8 losing coolant

A8 All/ S8 All
#1

Well, it seems the loss of coolant has been speeding up i think. Reservoir is dry this morning.

I dont see any leaks, nor do i smell hot coolant anywhere.
I suppose next step is to put some dye in it, pressurize the system and see if i can spot anything around the engine or reservoir itself.
no oil in coolant, or coolant in oil.

Anyone have this happen? Car was not overheated in our ownership, has just over 80k miles now.
Dont think its headgasket (i hope i should say)
Any other specific parts to go over?

#2

Expansion tank, any small cracks or leaks? They tend to go overtime.

#3

Dont see anything on the ground and dont smell anything when got.
switching over to summers next weekend, will pull off the liner and pressurize system to observe the area.
hopefully its something minor like that.

#4

Check the reservoir cup, actually replace it with a new one. Sometimes they wear out. Also check the coolant bleeder screw it’s on the left side of the engine when standing in front of the car. It might be loose try tightening it