I was at a red light when my car shut off n wouldn't start. After we checked the battery and oil, all of the water out of the coolant reservoir poured out onto the ground. We filled it back up, and a few days later I'm at the store and it all pours out again.
All of the water just literally poured out onto the ground. on 1997 Buick Skylark
Have the radiator cooling fans checked for proper operation. That's a good place to start with!