My engine is a 1980 Mercruiser 165 (GM 250ci inline six). My last trip out this summer, which was also my first this summer, there was a valve tapping along with decreased WOT rpm, around 3500, and a sudden overheat problem. I shut the engine down for about 5 minutes, then started it up again to cirulate cool water through the block. It cooled down to normal operating temp and I was able to bring her back in. I pulled the Valve cover off and found there was water in the oil all over the head (the white milkshake variety). When I checked the dipstick, the oil was very thin, about one half to one quart over full, but normal color. I pulled the manifold off and found there was rust in the shared intake port for cylinders 5 and 6, as well as a little puddled water. The manifold gasket was not in the best of shape, but the only excessively bad spots were on the high side of two exhause ports. I then pulled the head hoping to find a bad gasket, but the gasket seemed fine. The top of the 5 and 6 cylinders had a dusting of rust on them as well. I took the head to a machine shop to have them check it over and will get back to me in about a week. The machinist told me to plate over the exhaust elbow and add water to manifold and then pressurize it to see if any water was entering the intake ports within the manifold. I performed test, and did not notice any water. My question is what should I do to the engine while the head is being checked over and shaped up? I do not want to pour my retirement into an 1980 engine, but I also would like to have a reliable power source. Any help is greatly appriciated.
