Coolant loss

Just fixed the coolant hose connector. Emptied radiator added more coolant and started car to bleed air out. Coolant level dropped and we added more. The engine overheated so we loosened the cap slowly and let coolant bubble out. Test drove it and it drove fine. Second test drive it overheated due to low coolant. So the next day I topped off coolant and got car to normal operating system and it stayed at that temperature but the coolant dropped 4 inches in reservoir. No signs of leaks on ground. Any ideas on where the coolant is going?