Coolant level too low --> but only when its cold
okay guys so recently I started receiving a message on my dash saying that my coolant level is too low, but for some odd reason it only comes on when the engine is cold (over here in Winnipeg, MB it gets to be about -25 to -30 on average with windchill) like after I drive the car for a bit and the engine is warmed up, every subsequent stop and restart of the car, the warning message does not come on, only comes on when I leave the car parked outside overnight and when I start it up in the mornings to get to work. I don't notice any leaks or anything, and my car was only purchased 4 months ago from the dealership so I would have assumed that they would have topped it off.... does anyone have any ideas as to what is going on? any input is greatly appreciated.
2004 545i in Amethyst Grey with Premium Package, Cold Weather Package, Front/Rear Obstacle Detection System, Heated Rear Seats and Front Seat Power Lumbar Adjustment.