I just wanted to thank the OP for posting this.
I read it then decided to go home and check my reservoir tank.... it was bone dry as well. I waited till the engine cooled and checked the radiator which thankfully had coolant it. Not sure why the overspill tank would boil off like that I've never had a car that did that before but I know now to check that often as well....
Car only had about 6k on it at the time. Thanks again!
