[MBZ] When to check coolant level?

[Levi Smith]

When exactly are you supposed to check the coolant level in an 83' 300d?
I've noticed when mine is running there's nothing in the bottle (at least
when it's hot), but when I shut it off it returns pretty quickly to pretty
close to the line on the bottle.  Is this normal and I just haven't noticed
it before?  And is it just supposed to be at the line when cold?
Thanks!
Levi