I have a 350 chevy OMC engine a 85 Searay 26 ft sundancer. It has a Heat Exchanger and the level in that is holding full and has good green color from coolant. How can water get in oil from outside of the enclosed cooling system? Blowing a lot out the valve covers onto the spark arrestor and intake manifold. Any ideas?
Water can get into oil through a blown head gasket or cracked block. The fact that you described water blowing out of the valve covers makes me think it is a blown head gasket. You can check for a blown head gasket on your own by following the links below;
Obviously, if you have a closed cooling system and the coolant level is not dropping, you do not have a cracked block or faulty head gasket. If you did, the coolant level would drop.
rather sounds like you've got a blown headgasket
