Dont know where the core plug or penny as it used to be known is on your engine, once you get access to it simply prize out with a screw driver or players clean the area with a light wire brush put a bead of specialist sealant around and carefully tap the penny back in with a suitable size socket replace the anti freeze, The manifold might have to come off to get access in which case that will take longer than the repair.Someone might be along shortly to let you know about access. Hope this helps
