I have encountered a very strange problem. The boat is a 21' sea Ray with a Crusader 5.7 GM small block that was a replacement for the original mercruiser. Engine has 46 hrs, boat 146 hours. Fresh water cooling. Had a leak in the blocking gasket between the original mercruiser manifolds and the elbow, so I replaced them with brand new mercruiser dry gasket manifolds and elbows (post 2002 style). Boat was running fine. However, after sitting at dock for two weeks, I tried to start it Sunday. Engine was turing over, but not starting. Then it backfired, then progressively hydrolocked as I continued to crank it. All starboard cylinders had sea water, port side was dry and normal. How can this happen? The only way sea water can get into the exhaust is back up through the elbow, which is 18 to 24" above the water line? Always possible there was a casting flaw in the new elbows, but I doubt that, and not clear how the water would accumulate there with engine off. With the plugs removed, a lot of sea water came out.. suggesting the elbow was full! Could backing the boat while it is running cause such a problem, or a stong current on the stern while docked (it is in a tidal river). How would the water get there with the engine off and the boat tied at the dock? Even if a flapper valve is defective (have not taken it apart yet), I still don't see how this would happen while sitting at the dock? Any help apprecited.. really stumped on this one.
