Hope its not a blown head gasket, my z32 300zx at one point when it was completely stuffed after I bought it filled the overflow bottle and chuffed coolant out onto ground after shutting engjne off, pressure in cylinders was leaking past gasket into water jacket. Dont drain it, start it from cold with cap off, squeeze rubber hoses to try get air out, let it get up to temp in your drive way get thermostat open give some revs squeeze pipes, should get it bled out.