Dokus

Cls55 from 2005.

car runs well, no issue or warnings on the dash.

i have not driven the car for about 3 weeks. Two days ago i started the car and let it idle.

noticed that my coolant was kind of low, opened the cap and almost all coolant went down in the lines and have not returned. Is this normal or i'm just low on coolant? I have some white smoke but i think it's due to the weather and car not been driven. Exhaust and oil smells like normal.

I'm going to do major service this week and futher investigate for leaks and check oil but i got kind of scared when almost all coolant went in to the abyss. Normal?

rapidoxidation

No.
The radiator should be completely full and the reservoir should be filled to the max line when the engine is cool.
Is there any residual pressure in the upper radiator hose after the car has been shut down for the night?

Dokus

I went over the car today, found zero leaks. There are pressure in the tank after the car been on. Lines are soft. I added a 0.5L of 50/50mix mb 325.0 and let the car idle for about 20 min up to operateing temp. The coolant rised up a little bit from the max mark and did not went down when i opened the cap so it seems ok. Car runs like normal.

could it be that i have the orginal coolant that have just escaped over allmost 15 years?

if the oil looks ok i will just do a coolant flush and keep monitor the level