how to test for a cracked block

Howdy Gang,
We have a 496 engine in a Jet boat. The boat was washed down the river during a flood. It sat all winter long before we were able to remove and strip down the engine.

The engine had just 14 hours on it but after the flood it was full of muddy water.
We scattered it and cleaned everything- new bearings --plastigauged to check the factory specs. New gaskets and head bolts.

we did lap the valves, when the engine was put back together we spun the it over while it was still out of the boat and got good oil pressure with the test gauge.
Everything looked real good or so we thought.


we just put fresh water in the header tank but hear the water leaking into the base.


Any idea where to look for a leak-- or some method to pressure test it.
I haven't tried to pressure test the cooling system and could plug all the ports and test it that way. Maybe adding a dye to help .

I had a thought that maybe the head gaskets were not the correct ones.

Just want some ideas before ripping it apart
thanks
Hank
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Check with an automotive machine shop. There is a setup that can be used to pressure test a block while it is disassembled. Not all shops will have it. One of the guys that helped develop it lived down the street from me when I was a kid, so it's been around for a good while.

Look in the lifter valley and along the sides of the block in motor mount area and all along the line formed by the so-called "freeze plugs".

Blocks seldom survive freezing with water in them, they are usually cracked somewhere. You could cap off all the water ports and apply about 15 lb pressure to the cooling system. Remove the oil pan and watch for water .If it comes out of anywhere but the head gasket, put a fork in it, it's done

My first thought is that if you've got a big enough leak to hear the water it's not gonna be a head gasket, and you're likely wasting your time on a severely cracked block but both Mike and Seth gave good advice.

thanks guys
must be the time to look for another engine
Hank

A few years ago a friend of mine had a boat with an IO the engine would fill up with water while sitting at the dock. We took it apart several times checked every thing we could. Finely a shop said it could be in your exhaust headers. We tried testing them several ways but just couldn't get it right. The owner made a deal with a shop that had a used set on the shelf. We put them on and all was good. Just something to try cheaper than a block but not by much

I'd check the exhaust manifolds for sure. Since they are water cooled there is a good chance they are cracked. My Dad had similar issues on his I/O pontoon boat and his intake and exhaust manifolds were cracked due to the previous owner never winterizing it.

The crank and all the rotating parts look good so I'll try to find a block -after I test the manifolds
thanks
Hank