Smoke in the cabin and my theory

chartscharts · #1 (**permalink**) 09-25-2011

This weekend, my 11 year old son and I went sailing. No wind in the morning so we motored (Farymann) for about 90 minutes. This is a new boat to me and while we had run the motor several times before without problem, this was the longest we'd run it. We also ran it pretty hard, keeping the speed up. I wanted to see how it did under load for a bit.

It ran great but after 90 minutes or so, my son noticed smoke/exhaust, something in the cabin. Not enough that you couldn't see through the cabin but enough so it'd be uncomfortable to breath.

I shut the engine off, he took the helm, and I went below to look for a fire by the engine...none was present. I opened some windows/hatches to clear the smoke out, then looked in the engine compartment again to see if I could see where it came from. Of course, with the engine off, I couldn't tell but got the general impression it was coming off a wide area of the front of the engine.

I was about to start the engine again to see if that would reveal where it came from but my son suggested lunch first. That way if the boat blew up we could tread water on a full stomach; an excellent idea.

After lunch, I fired up the engine, and it ran fine for a few minutes, with no evidence of any smoke anywhere. I shut it off again, and we sailed back toward home. When we got close, I fired it up again to dock and it ran for about 15 more minutes without any signs of smoke or trouble.

My theory: There's some grease/grime/oil on the surface of the engine. It was on my to do list to try to clean that up and find the source. My theory is, after running a longer time under load, it got hot enough to burn the oil off the surface, causing the smoke. That explains why it didn't smoke after lunch, or going back to dock, or the other times we've run for shorter periods with no problems.

To test, I was going to clean the engine surface of that stuff, then run again for 90 minutes under load and see if it returns, and if it does, try to catch it in the act and find the source.

Is my theory crazy? My test plan crazy? Other thoughts?

-Charts

MarkSF · #2 (**permalink**) 09-25-2011

No your theory and testing approach sounds quite reasonable. Another theory is that it's an accumulation of diesel fumes due to motoring with a following wind. The other day after motoring for a while my forward cabin CO alarm went off, so that's proof that exhaust fumes really can accumulate in the cabin.

You could have a slight engine oil leak somewhere. Valve cover gaskets are a popular oil-leak source, and that could easily run down the front of the engine.

jrd22 · #3 (**permalink**) 09-25-2011

More than likely that your theory is correct. It could also be a small oil leak that just needs enough time to reach something hot (exhaust manifold?) and cause it to smoke. Check the valve cover gaskets for signs of fresh oil.

Faster · #4 (**permalink**) 09-25-2011

Another possibility is that there's enough 'blowby' from the crankcase to overcome the crankcase ventilation - allowing hot oil vapours to invade the cabin space. This may only occur at higher rpms/loads, where as at lower speeds the suction of the intake can handle these fumes..

Hopefully your other theories prove correct, because this might indicate that a ring job would be required.

epaolino · #5 (**permalink**) 09-25-2011

check your exhaust riser for leaks.. they may have pin holes.

chartscharts · #6 (**permalink**) 09-26-2011

Good ideas, thanks!

BubbleheadMd · #7 (**permalink**) 09-26-2011

Is this a diesel or an Atomic-4 gasoline engine?

If you have an Atomic-4 with the slash-cut rubber tube pointing down into the flame arrestor, these engines are known to smoke a little bit under load. If you get the PCV valve modification from Moyer Marine, the engine runs better and does not smoke.

If you have diesel, ignore what I said, and continue with your existing plan.

deniseO30 · #8 (**permalink**) 09-26-2011

I've a friend that has a Farymann in his boat. He had exhaust leaks from the exhaust manifold. Also he's had problems with head gaskets. Not sure what engine you have but I'm sure it's not the V2 type that he has LOL

BubbleheadMd · #9 (**permalink**) 09-26-2011

Denise- Farymann is a diesel engine? Oops, I thought it was a type of boat.

hellosailor · #10 (**permalink**) 09-26-2011

All good things to chase but, but I'd also clean down the engine first to get a good look at it, and at any possible leaks.

If the seller repainted part of it with conventional or engine paint, a good hot run can cook that and send off smoky fumes, which would stop when the paint cured. Or cooked off.