Mercruiser 470

I just tuned up my 1986 Wellcraft 190 which has a Mercruiser 470 (170 hp). I also replaced the 90 weight fluid in the transom. Motor starts excellent. I recently placed the boat in the water to test (and yes I put the plug in). After about 20 minutes, the boat started to take on alot of water. I lifted the motor hatch and saw that the water was the whole way up to the engine and starting to seep onto the floor. I gently headed back to the ramp and removed the plug (alot of water drained out). Another boater said it might be the gimble boot? Once the water was drained I looked for any hoses that might have been split or had come off (no avail). Should I hook up the garden hose and start the engine to test (to see if water might come be coming in through the transom)? This boat has always been stable, but I am at ends with what to do. Any suggestions? Thanks

Re: Mercruiser 470

You can run it on muffs, but it probably won't leak.
Leave it on the trailer, and back it into the water and take the time to look and see where the water is coming in at. The ujoint bellows and the shift cable bellows would be prime suspects, or around the perimeter of the tranasom sheild (usually due to rotten transom) but until YOU locate the leak and tell us where it is, there is no way to tell you how to fix it.