Hi All I am new to the SeaRay family (Queensland, Australia) and we have purchased a Sundancer 275 that has a Mercruiser 350 MAG MPI and Bravo 3 drive. We were out on the river last weekend and noticed minor vibrations prior to anchoring for the day just off the beach. When it was time to leave, the boat wouldn't start. Ended up being a starter motor failing due to the engine being hydrolocked. The mechanic took the exhaust manifold off (I took the starboard side off yesterday) and there is water in one cylinder on the port side. All other cylinders on the port and starboard side look fine to me, no signs of water in the exhaust ports of the cylinder heads however there is water in the oil. (I couldn't inspect port exhaust manifold for cracks due to it being locked up in mechanics shop) The mechanic has simply seen the water and told me that I need a new long block because there is a hole in the cylinder head from corrosion and it will cost us $10,500 installed. I don't agree with that outcome by simply seeing some water in only one of the cylinder heads. It is quite an extreme diagnosis for doing no real investigation other than seeing water in the exhaust port of one cylinder. I have asked the mechanic to put the boat back in the water as we will need to "save" for this.... I really want a second opinion. I want to do a compression test on the cylinders and possibly remove the intake manifold, cylinder heads and head gasket to inspect these areas as well as pressure testing the exhaust manifolds and risers etc. I just cant accept that I need a new long block for water in one cylinder. He may very well be correct but Id like to do my own investigations. In saying all of this, the boat will be back in the marina sometime this week. My question is, how far can I tear down the engine without water entering the boat? (raw water cooled) I assume I can block off the raw water intake hose to prevent any water entering or will the water simply not enter due to the fact that the water pump is not operating. Sorry if any of this has been covered in other posts. I just want to do my own investigations and get a second opinion before we go to the extreme lengths of replacing the long block. Thanks everyone!