Why does antifreeze come out when the car is hot?

Why does antifreeze come out when the car is hot?
It has expanded as far as it can inside of the engine so it has to go somewhere!
See if you have enough anti frez ( what till the engine cools down first ) or make sure if the mixture of water/anti frez is correct 30% water to 70% anti freeze .
Check your thermostat.
If the coolant is coming out of a weep-hole on your water pump, pump is bad.
Check the hose clamps, soft hoses.
plug up radiator, heater core.
Even if you have had service done on your car, you may have and air pocket in your system, they didn't burp the system right, take it back.
also make sure the antifreeze, "if a mix yourself fluid" has distilled water mixed with it. distilled water has a higher boiling rate than water with impurities, thus preventing boil out.