I have a 2001 Honda 90 four stroke outboard. My son overheated it. I had it rebuilt by a local repair shop. Initially there was no water in the crankcase mixed with the oil. After rebuilding the motor they ran it on a set of earmuffs to check it in the shop. Runs great, no problems on the muffs. When you put the boat in the water and run it, The crankcase immediately fills to the top with water. Somehow the exhaust back pressure is causing the crankcase to fill rapidly with water. The shop has done all it can to this and it is evident that they were not very experienced at this model of outboard. I am trying to get some suggestions as to the cause of the leak. Is it the block, the head or did they not put it back together correctly. I cannot find a knowledgeable mechanic for this model in my area. Any help or testing techniques are much appreciated.