That's a really good question Mine is doing that too. It's also overheating. Maybe we could collaborate for answers?
radiator cap might be leaking
in the overflow tank
Overflow Bottle.
It could be a couple of things. The coolant system could be over full. There could be a clog in the radiator. Or possibly the thermostat but not likely. also, the ford coolant tank is pressure sealed, if the cap to the tank has a defective seal, it WILL overflow when you stop your car, or whenever the pressure builds
On the coolant overflow bottle
head gasket
The coolant goes into the overflow bottle on the passenger side, fill it cold and do not over fill.
dex-cool coolant---it is orange in color.
Sounds like a blown head gasket
Low coolant or bad sensor
Clean the reservoir and flush the cooling system.
Thermostat may not be opening