Where to look for water leak

[Skidude17]

I am getting a large volume of water in my bilge.
I have a '95 Mercruiser MCM 5.7L SN 0F59836545 in a 22' SeaRay. Early in the season the exhaust bellows tore, and that was the first time I got this large amount of water in the bilge (I know that's not where the water is coming from). I hadn't changed the bellows since I owned the boat in 2019, so I figured it was time to change them all. When I say a large amount of water, there was so much that got in there from my early season test run, water made contact with the starter and blew the starter.
The heavy flow is still happening. After I changed all the bellows, I took it to the boat launch and let it sit in the water for a good 5 minutes. The bilge was bone dry. After I started the engine, inches of water showed up very rapidly. There isn't any water when I run the engine on muffs. I ran it for at least 10 minutes on the muffs, and not a drop of water. Where should I start looking for leaks? My initial thought was the y-pipe, but I would think there would be some water coming through when running off the muffs.

 

[Stinnett21]

Sounds like cooling water from somewhere. Investigate with phone on a selfie stick.

 

[nola mike]

Exhaust bellows won't cause a leak. Should be obvious based on that volume, but make sure all of your drain plugs are in, check core plugs in addition to hoses to the ps cooler and exhaust boots. Assuming you'd see a leak in the front. Just to make double sure, see if it leaks on muffs

 

[bajaman123]

Put the drain plug in.

 

[airshot]

With that much water coming in, it will be very noticible, so gotta get in there and find it some how....Phone is your friend here...

 

[Scott Danforth]

Could be transom, Y-pipe, u-joint bellows

 

[Chris1956]

A lot of those V8 MerCruisers have a belt driven raw water pump. If may not leak when the engine is off, but leak when the engine is running.

 

[Lou C]

Also check the core plugs in the engine block, the clamps on the exhaust rubber hoses, Y pipe to inner transom joint
This is one big issue with I/Os
many places to leak water and most are inaccessible with the engine in place.

 

[Scott Danforth]

The OP ran the motor in muffs for 10 minutes and no leak. So it's not core plugs or leaking hoses. Since the exhaust bellows is bad, my guess is the shift bellows or U-joint bellows also is bad or the transom is bad, which would only leak in the water

 

[nola mike]

The OP ran the motor in muffs for 10 minutes and no leak. So it's not core plugs or leaking hoses. Since the exhaust bellows is bad, my guess is the shift bellows or U-joint bellows also is bad or the transom is bad, which would only leak in the water

Actually he said it didn't leak in the water. Then said it didn't leak in muffs...
Definitely needs to figure that out first