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Ask Dominick Your Own Question
Dominick, Marine Mechanic
Category: Boat
Satisfied Customers: 1009
Experience:  25 Years Experience as Mechanic, 20 Yrs Boat Yard Owner/Mechanic, Factory Certified
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Maybe you can, I hope. I have twin 350 Magnum Mercrusier engines

Customer Question

Maybe you can, I hope.
I have twin 350 Magnum Mercrusier engines on my 2002 Rinker 342 and have water intrusion into my Starboard engine cylinders on the port side. Never overheated but hydrolocked last summer. Pulled motor and rebuilt because the starter bolt sheared off and had to anyway. Megged the block and its good, honed the cyliders because the water sat on top replaced Pistons, Rings and Lifters. All new Manifolds and Risers, gaskets ect. Checked Heads and Intake Manifold with all new gaskets. Rebuilt Raw water pump and installed new Water Pump with new Thermostats and inserts.
Guess what... Same problem.
What am I missing and doing wrong?
Submitted: 2 years ago.
Category: Boat
Expert:  Tan replied 2 years ago.
Hello. Did you check the shutters in the collector pipe? Could I get the engine serial number please?
Expert:  Tan replied 2 years ago.
# ***** is the shutter. This prevents water from backing up through the exhaust.
Customer: replied 2 years ago.
Not a Professional, Sorry. What I call Exhaust Water Backup Baffles are working well.
Serial # ***** Engine is 0M075548
Expert:  Tan replied 2 years ago.
Ok what cylinders are you getting water in? When are you getting water in the cylinders?
Customer: replied 2 years ago.
There was water in cylinders 1, 3, 5 and 7. I also never had water in the oil. Water intrusion upon starting of new rebuilt engine, same as before rebuild.
Expert:  Tan replied 2 years ago.
Ok the only way water gets on the tops of the cylinders is through the manifold , riser or a bad cyylinder head. Did you have the cylinder head magnafluxed? Try this disconnect the water hose to the manifold. Start the engine does the engine get water in the cylinders again? Run the engine till the manifold start to get hot.
Customer: replied 2 years ago.
I do not think the cylinder head was magnafluxed, also which water hose should I disconnect from the manifold? The boat is currently stored on land with all of the spark plugs removed.
Customer: replied 2 years ago.
Can you please send a diagram of the cylinder head assembly?
Expert:  Tan replied 2 years ago.
You should have only the one hose on the bottom of the exhaust manifold. You can just pull the hose off and let it go into the bilge or plug it. I'm thinking the head is the problem as the manifold and the riser is new. The shutter is good. The only thing left is the cylinder head. It won't be the engine block as you would have water in the oil. So just by process of elimination the cylinder head is the problem. The only other possibility ios a bad manifold or riser not likely but this test will eliminate them as a possibility. Does this make sense?
Customer: replied 2 years ago.
We pressure tested the water system through the hot water heater hose, with the manifold hose plugged. We were getting a large volume of air through the exhaust manifold and riser, as we disconnected the exhaust elbow from the shutter assembly. The intake water hose was plugged as well. We thought this isolated the water system from the fuel system.
Expert:  Tan replied 2 years ago.
That tells me the cylinder head is cracked. The fuel system has nothing to do with the cooling system. With the manifold water supply disconnected from the system and the water supply blocked off the system should hold pressure. With you hearing air in the exhaust manifold that tells us the cylinder head is cracked. Do you follow that?
Customer: replied 2 years ago.
We are not sure that the starboard manifold water hose was plugged, but the amount of air that came out of the port side exhaust system made it sound like a French horn. This would not seem to be from a crack, could it? Would you also have a diagram of the cylinder heads?
Expert:  Tan replied 2 years ago.
The system should hold pressure with the manifolds out of the system and the water supply to the engine blocked off the engine should pressure if it doesn't the head is bad. Now if you didn't have the manifold blocked off it will let air out. Which view of the cylinder do you want to see?
Customer: replied 2 years ago.
So you think the cylinder head might be bad enough to let that much air through to the exhaust manifold? The Engine was rebuilt by a professional engine performance shop who supposedly verified that this was all checked and verified with all new Gaskets top and bottom. I will check all of your valuable and informative recommendations out tomorrow. Can we continue this tomorrow after I check all this out?
Expert:  Tan replied 2 years ago.
Absolutely. If the cylinder head wasn't magnafluxed you can't see cracks some times. This is the only thing that fits the problem. As long as you don't have a defective manifold or riser which is highly unlikely as you have the same problem you had. Before you replaced the manifolds and risers. Now you have a new manifold and riser. The cylinder head is the only thing that will allow water into the cylinders. The engine block would let water into the engine oil.
Customer: replied 2 years ago.
That would be catastrophic at this point. I will get back to you tomorrow with some further information. Just so you are aware, there are 3 certified Marine mechanics working on this and cannot ascertain this problem. More tomorrow. Please hang in there.
Thank you for the insight. Steve
Customer: replied 2 years ago.
Checked with the Engine Shop this morning and they confirmed that they did magna flux the Cylinder Heads and they were fine and said that typically even if they some how missed something that this would usually effect one cylinder but not all 4 and it sounds like a port side distribution issue effecting the whole port side.
Expert:  Tan replied 2 years ago.
Ok let make this simple. Remove the exhaust manifold on that side of the engine. Connect a water hose to the water heater hose. Block water supply coming from the drive. Disconnect the water hose going to the other exhaust manifold. Turn the water on does water come out the exhaust ports? This way the only issue can be the engine eliminating any other out side source. Meaning the machine shop missed something. I don't know what they mean by distribution system. The thermostat housing distribute water to the manifolds and the circulation pump. If you eliminate the manifold how does water get in the cylinder if it isn't internal to the engine? How is it the engine block without water in the oil? What is left that will put water into the cylinders. Does this make sense?

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