its a one way leak, it only pushes exhaust gas into the engine, only loss of coolant is out the rad cap.
i got the same issue. while its flushed to water, once its clean water add blue devil all your problems will be gone. then only remove the coolant from the rad, and add one gallon of straight new coolant to it after you follow the directions on the bottle. you want as much of the treated water to stay in there. so dont drain the block. i used a thin tube in the rad and siphoned it out.
then down the road you can do head gaskets or blow it off like most will cause its still not loosing coolant.
