You are probably getting water coming in from the exhaust.

It happened on a boat I taught on when in big following seas.

A flapper valve on the exhaust would help. I have a gate valve on
mine, and I'm considering putting a ball valve on it to make it
easy to secure.


Barret Bonden wrote in message
link.net...

Universial Atomic 4 (inboard , salt water cooled) - 2 years ago I found
salt water in 2 cylinders and my mechanic suggested and then did a head
gasket ; she ran fine for 40 to 60 hours of use, and then - more water in
the aft 2 cylinders nearest the exhaust ; I was in rough seas - and
there
is a possibility water sloshed it's way back up - I did some work on the
system to make this less likely, and used the engine for 10 more hours ;
worked fine - and then it happened again, in seas much less rough but
still
rougher than the prior 10 hours - so my question is , can a head gasket
fail randomly ? Can it hold most of the time and then give out , and then
hold again, or is this a matter of water working it's way back up through
the exhaust ?