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2004 Monsoon 340 smokin at cold start

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Posted (edited)

My problems started in 2020 when my impeller went out and I ran the boat for about 100 yards, to get to the dock, with the warning light and buzzer sounding. This boat always ran perfect. Always started on the first crank with no throttle. It now runs slightly (very slightly) rough when hot and needs throttle for cold starts (after sitting for more than 12 hours). When it's cold it also has a blue smoking problem for about a min or 2 then you don't see any smoke while running or on a hot start. I cleaned the intake out well and that seemed to help. I'm having a hard time figuring out how oil is getting into the cylinders. Some additional info: after the over heating incident I had to add transmission fluid for the first time in the 8 years I've owned it, I changed oil and filter (no water in those) I replaced all the plugs, pcv, cap and rotor, I haven't needed to add engine oil so it doesn't seem to be burning any (even though it seems like it for 1 or 2 min after it hasn't been ran for a day or two). Could it be burning transmission fluid? I remember a night when I was in High School my modulator valve on my 1972 Cutlass went out and I looked like I was James Bond sending thick clouds of smoke making it impossible to drive behind me...do these boats have anything similar that might not be totally broken but enough to let trans fluid seep into the cylinders?



Edited by NorrisJunky
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@NorrisJunky - From your description can we assume you mean smoke out the exhaust pipes?  Blue smoke on start up coming from the exhaust pipes tends to be valve stems seals or valve guides (worn or scuffed allowing oil to drain down them) which then disappears once running.  The oil pools up on top of the stems and drains in to the intake port.  Another culprit could be scuffed cylinder walls allowing oil up past the rings although this would tend to be a more constant smoking problem rather than just a start up issue.  To confirm the source I would check the amount of blow by coming from the PVC hose, run a compression and a leak down test.  If those tests look good, that points to the valve stem and/or seals.

There is no connection between the transmission and any combustion part of the engine.  Your transmission cooler could allow transmission fluid to escape in to the water passage which would then exit out the pipes although it would not result in blue smoke, just oily exhaust fluid mix coming out.  Hard to 

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Yes...the smoke is coming from the exhaust pipes. What I was looking for could best be described by your valve stem seal theory. I was deducing that the oil was getting into the cylinders over a long period after shutting off, the longer the period the more it smokes. So anywhere between 2 and 24 hours seems to produce an increasing amount of smoke after 24 it doesn't get any worse. Once that burns off it wont smoke unless it sits again.

I believe your comment that there is no connection between the transmission and the combustion part of the engine but if (I still don't know if there is a modulator valve) there is a modulator valve, aren't they controlled by a vacuum line off the engine so if it fails drastically the engine could start sucking transmission fluid? I know not many modern engines use a modulator valve but this is a 2004 boat engine so I'm just not sure. I might be showing my ignorance because I'm not 100% versed on what the modulator valve even does. I'm only hung up on that because the transmission was down fluid for no apparent reason and I tend not to believe in coincidences. You know, boat overheats, burns oil, runs poorly and by the way it needs more transmission fluid (enough that it stopped going into reverse until I added some) all around the same time.  :)

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Keep in mind that when you overheated the engine you also overheated the transmission. The trans might have built up enough heat and pressure to burp fluid through the vent on the top of the trans causing your low level problem.

There's no modulator valve on your boat. I believe those were for controlling shift points/firmness in multi speed automatics so there's no need in a marine application.

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