Did you burp or bleed the air our heater core? This is just a helpful tool it is not required. A Radiator Coolant Vacuum Refill Kit sure does help the process. They work like a champ, plus you can also tell if you leaks. It will suck down the hoses flat and put a vacuum on the water cooling system. Then you flip a valve and the vacuum in the system pulls the fluid from a bucket or what have you back into the cooling system.