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I think i have a craked head

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I took my wife and gran daughter out for a ride on the lake the other night.

Was a great evening for a ride.

To get to the point, I looked back and there was steam and smoke coming from under the engine cover !

When I checked the temp gauge, it was still in the 120-140 degree range, ok, not over heating.

When I opened the cap for the cooling system, it was bone dry, and HOT.

I had just checked it 20 minutes before, when I did my pre trip.

Check oil, water, belts and fluid levels.

Well, I refilled the tank with water, and limped into the dock.

Next day, I went down and started looking.

There are no broken hoses, or lines. No water is showing up in the oil. (Thank fully)

Now, when I started the engine and let it run at high idle, it started to spew

steam from the vent on the valve cover!

Can you guys help me make an educated guess as to what might be wrong ?

Thanks in advance, Bill.

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Ideally a cylinder leakage test would be the most accurate test for cylinder integrity. Justtrollin's method is a good indication of a head/gasket problem. When you pull the plugs out you can bring each cylinder to top dead centre and visually inspect the top of the piston. The pistons will have carbon on them. If you have coolant leaking into the cylinder the top of the piston will be clean instead of carboned up. Also you can drain the oil from the engine and see if any water comes out. It will come out before the oil.

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Most likely the head gasket has failed in the area that goes from cylinder to water jacket. This type of failure will not dump much if and water into the oil, but will do like others said. Get a compression tester and check compression. An easy way to tell is, if theirs pressure in the cooling system.

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Is your system a closed system, if so you could obtain a block tester that reads the amount of combustion gases in the cooling system. Thats how we do it on cars anyway. Then also if not sure do a cylinder leakage test like stated earlier. A cumbustion gas tester is just a blue fluid in a container that turns yellow or greenish when gasses are present

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yes, it is a closed system.

There is NO water in the oil. The only place I can find ANY water at all is on top of the head, under the valve cover.

I have a bunch of spare parts for this motor, MercCruiser 488. So, changing heads is not a real problem.

Thanks for all the input, I really do value the info. Bill.

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The water ounder the valve cover may due to condiensation when she first got hot...If you have a cast iron exhaust manifold it is probably cracked under the riser area very common on the 488..When they crack it warps the gasket area an the coolant seap into the exhaust...Merc made the replacements out of aluminum

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