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Onan 4.0 MCCK Marine Genset Water in cylinders/oil

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Old 10-18-2013, 10:11:51 AM
boatingdrew boatingdrew is offline
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Default Onan 4.0 MCCK Marine Genset Water in cylinders/oil

Hi everyone,
I have an Onan 4.0 MCCK-3CR/1H Marine Genset, Serial number: 1790420116.
It has gotten little use this year but like a trooper has always started easily. Last week when I went to change the oil before winter storage it wouldn't start. I cranked it several times, never for more than 10 seconds, and waiting a few minutes each time between attempts. However in total I tried many times and then my mechanic tried several times without success. This past weekend I changed the spark plugs and noticed they were wet. I used an old battery hygrometer and drained water and gas from the cylinder (only one had fluid in it). Once the cylinder was dry and spark plugs were changed it started right up again and runs well, albeit somewhat rich. My mechanic changed the oil and noted that there was a substantial amount of water in the oil. He suggested the water I noticed in the cylinder might have come from all the cranking and water from the exhaust flowing into the cylinder. Could this have also contributed the water to the oil? He is going to compression test the cylinders but suggested that the engine may have a blown head gasket, or worse possibly a cracked block.
I am wondering weather or not I should try to investigate the problem over the winter or weather I should tune up the engine and run it for a while in the spring and then check the oil again for water. Could the water just be from all the cranking? Has anyone else experienced this?
Thanks everyone for your advice.
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Old 10-18-2013, 10:34:36 AM
Graycenphil Graycenphil is offline
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Default Re: Onan 4.0 MCCK Marine Genset Water in cylinders/oil

Is it water or antifreeze? That will make a big difference in diagnosis.

Is your mechanic competent and trustworthy? If not, either work on it yourself or find someone you are comfortable with. This might (or might not) have a simple solution, but an incompetent or crooked shop could turn it into a huge project.

The one thing I will say is you should not do is just let it go till the spring.
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Old 10-18-2013, 10:48:39 AM
Jim Rankin Jim Rankin is offline
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Default Re: Onan 4.0 MCCK Marine Genset Water in cylinders/oil

There is a considerable amount of water that will collect in the exhaust system from running an engine with a cold exhaust system. Normally when the engine is run until it is warm, this condensate is turned back to steam and when the engine is shut down, there is not enough remaining to cause problems.

Unless you can think of something that has changed since the last time you ran it that would have introduced water into the exhaust system or allowed it to collect there while the generator was running, you most likely have a leak. Any bad storms, any new exhaust components installed, changes to the routing of pipes etc?

Most likely you have a bad head gasket and a new one will cure the problem, but could always have more serious trouble like pitting through the water jacket into a cylinder from poor coolant maintenance or crack from overheating/freezing etc. This generator does have a raw water to coolant heat exchanger doesn't it? It doesn't use raw water directly in the engine does it? I'm not the one to tell you the final best information on this one. Someone else with some experience with the MCCK can do a better job.

If it were mine, I would either compression test it (but if it runs fine, I doubt that is going to help much) or rig up an adapter you can purchase for some size sparkplugs at autoparts or break the ceramic of an old plug out and attach a fitting to the metal shell to put compressed air into the cylinders through the spark plug holes.

Turn the engine so the piston in the cylinder to be tested is at TDC of compression stroke so both valves are closed, find some safe and secure way to hold the engine there and then apply up to 150-200 psi air pressure to the cylinder and see where it's going. The reason for holding the engine is so if it is not quite at TDC, it will not spin suddenly as you apply pressure.

There will be some air leaking around the rings into the crankcase in any engine, even a brand new one, but if you get bubbles in the cooling system, you know you have a leak in that cylinder. This process also checks the valves, simply listen at the carburetor and exhaust for air blowing.
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Old 10-18-2013, 01:32:42 PM
grif grif is offline
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Default Re: Onan 4.0 MCCK Marine Genset Water in cylinders/oil

Lot of the same issues and information. Might be worth a look
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Old 10-22-2013, 12:10:40 AM
boatingdrew boatingdrew is offline
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Default Re: Onan 4.0 MCCK Marine Genset Water in cylinders/oil

Hi everyone,
Thanks for your feedback and advice. I have been busy winterizing the boat and yet haven't had a chance to compression test but my mechanic is set to do so this week and I will give an update.
To answer you questions:
1) The generator is raw water cooled
2) There have been no other changes to the way the boat sits in the water, or any other changes to the exhaust system.
Thanks again everyone
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