Pulled all the plugs out of my 350 Mag and water shot out of the #3 cylinder like a high pressure garden hose.

Vote on what you think the problem is, and I'll post after its fixed.

BUMMER! Sounds like quite a few of us wont be making it to the islands anytime soon

I could have come in via an exhaust issue.. It's easy to pressure check the exhaust first then take the motor apart. Good luck

Yes I agree with OSOsweet.. My dad's boat had same problem . It was the exhaust manifold. He had it pressure checked it was cracked. If I were you I would check both.

I vote cracked manifold.

It is probably not an exhaust manifold. If the manifold was cracked it would not allow THAT much water into the motor. For water to reach the piston it would have to go back through the cylinder head, through the exhaust valve and into the combustion chamber while running. Sounds like a head gasket or possibly an intake manifold gasket/bolt issue to me. Would love to hear what it is when you get it fixed. Good luck regardless!!!

Did a pressure check tonight on all the cylinders. The one thats blasting water out is about 30-40# higher than all the others.........

compression or leakdown test?

Compression

check your exhaust valve spring.