Check your thermostat.

 

check thermostat as gordo said .. and if the car is actually spitting up coolant thru the bottle.. then i wud definitly check the water pump.. pull it of and see if it has any blades left.. if not then thats the problem.. also check if fans are on high speed when over heating

 

If you go that far, then replace the plastic t-stat housing with an aftermarket metal one. Cost about $90.