Dark Grey smoke – Port engine

[Stephen Oliver]

So I suspect I know the cause but just prearming myself for what else can be wrong.. 

Off out at the weekend – 47ft flybridge running 2x 1993 6bta 330’s Boat is dirty underneath and is due out in a few months but i’ve not had time to dive it.

A few km from out departure we noticed that the port motor sounded different (we have wet mufflers) and the exhaust temp was elevated a little (8degC) over the STBD engine. Engine temp was steady though. We also noticed that the exhaust was dumping some dark grey smoke (not typical black under load smoke) back the engine down from 2100rpm (our cruise revs) and smoke dissapeared. Decided to head back to the dock – was kind of expecting a  burst turbo hose – or worn turbo again.. hoses all ok – turbo corroded but not as bad as we have seeen previously.. motor ran below 2100rpm solidly for another 30 minutes. Idles fine etc.

It was due a good service so turbo is off for recon (its an ongoing ’roundtuit’ where I will redo the exhausts as per SBmars spec – or as close to as I can) its been 5 years since it was last done and resleeved, and looks ok to do again (and relatively cheap in the great scheme of things). Aftercooler is getting full strip clean pressure test ect as is the heat exchanger. Manifold is sooty but dry no evidence of corrossion in it.

So apart from the turbo either a) having insufficient boost to deal with the filthy bottom and just doing its best causing smoke and elevated egt’s or b) the oil seal passing at higher revs and dumping oil into the exhaust (no evidence of this happening though) what else could possibly cause the dark grey smoke… certainly seems a case over overfuelling and insufficient boost.. but just looking for pointers?

Maybe this winter (aus) will be the winter I actually fix the exhausts! 🙂

Steve

 

Topic

[Stephen Oliver]

Tony If I remember right we get to 2850rpm with clean bum and loaded per usual – so not overpropped terribly in ‘normal’ conditions. But we could probably do with an inch taking out.. This is a new issue not an existing one. This is not normal in the sense of end of season – wierd growth year – hull doesnt normaly get dirty but it is..  and more a question of what else could be wrong beside the turbo, given the engine was running nicely at low speeds (sub2k). I know the turbo issue is my making, by keep on putting off the inevitable exhaust design and manufacture. Unfortunately there are few companies here that can do such and even fewer that can do it well. I can design and draw it.. i just dont have the fab skills. The only place i’d probably use is 3000miles plus away on the other side of Aus so makes it a bit more difficult.. This is compounded by having limited room for changing mufflers and limited head room (should be able to get about 8-10″ of rise though) for decent risers..  Thanks Steve

[Tony Athens]

Unless you can reach an accurate 29oo RPM  with your 330’s, under   fully loaded conditions, you are OVER PROPPED in my book …… Squeaking an accurate 2800 RPM is for a test cell on a dyno under perfect conditions.  Your call    

[Stephen Oliver]

Sorry I didn’t word that well.. I mean typical black smoke when a deisel is overloaded. We aren’t over propped as we don’t normally have any smoke or have a faint barely visible smoke toward the end of the season down to the growth.. apologies for that..

[steven.borcherding]

Follow-up

 “We also noticed that the exhaust was dumping some dark grey smoke (not typical black under load smoke)”

If you typically experience black smoke under load I wonder of you are over propped? 

[Author]

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