sounds like you need to do a radiator pressure check put pressure check tool on your car in place of radiator cap; run car for 10 minites to open thermo stat then turn off motor pump up gage and coolant system leak will be exposed the more you pump the more pressure and air and water have no where to go except out of leak you should be able to find leak eaily since it should being spraying under presure had a pin hole one time, never could find the leak thermo stat would close and leak would go away .
did the pressure check, turned motor off started looking found it in about 2 min, it was a heater bypass hose took 2hr to replace hose but 2min to findlooked for weeks would never have found it