I hooked up water to my girlfriends 1986 Mercruiser 260 Alpha One and started it up to get it ready for the summer and the manifolds got hot. I opened the drain petcocks and no water.I don't know anything about Mercruiser outdrives. Where is the pump with the rubber impeller located? Is there anything else that could be the problem? I have replaced such a pump on an old OMC I once had, is it a difficult job on the Mercruiser?