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Onan 6.5 MCCK spec. H blows blue smoke


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Old 08-09-2017, 04:02:01 PM
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Default Onan 6.5 MCCK spec. H blows blue smoke

Greetings folks. First post after a long time lurking. I just never had anything that I was able to contribute, I avoided making useless comments that did not meaningfully add to the conversation, and I never had anything break. That has changed!

While under a light load, my closed-cooled Onan 6.5Kw MCCK spec. H that is mounted in my mid-80s boat started blowing copious amounts of blue smoke out of the exhaust, and sounding very unhappy.

I searched the forum for these symptoms, but came up empty. I was not able to do any troubleshooting before I left the boat.

I'm looking for ideas on where to start troubleshooting first. There was so much smoke that I'm sure it is oil-related, and not fuel related like a stuck choke or something. While I expect to eventually find out that it is a cracked piston or broken ring(s), I prefer to start with less invasive diagnostics first. What are your thoughts?

This is a great forum here. I especially like the sticky on the MCCK electronic ignition conversion.
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Old 08-09-2017, 04:32:11 PM
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Default Re: Onan 6.5 MCCK spec. H blows blue smoke

Maybe your altimeter is off and you're below 0 msl. Lift it up a foot and it should be good to go. Ok I joke...

I'll assume the smoking is a sudden problem and not chronic due to simply a worn engine. Or is the oil way overfilled and the breather is pushing oil out into the intake.

Is the oil diluted with gas? Smell the dipstick. If it smells even a little bit like gas change the oil and run it again. Dilution would be from a carb that leaks gas into the engine. Let us know your findings.
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Old 08-09-2017, 04:33:51 PM
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Default Re: Onan 6.5 MCCK spec. H blows blue smoke

How many hours on it. The most common thing I found on most boat units. Never had a good load on them. Some would run them with a light load or no load at all. I would try a good load see what happens.
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Old 08-09-2017, 04:34:36 PM
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Default Re: Onan 6.5 MCCK spec. H blows blue smoke

Posting the full model and serial numbers would help. Beyond that, the first thing I would check is the oil level. If it is over full, a leaking fuel pump diaphragm could be filling the crankcase with gasoline. Also check the PCV crankcase vent. A plugged vent could cause high crankcase pressure.
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