View Full Version : Black discharge from engine on water
04-29-2007, 03:37 PM
I have a 95 maristar lt1 closed cooling. I ran the boat several times this year since winterized. Last week when I started it, there was a puff of blue smoke (could have been exhaust) and a black discharge floating on the water behind the boat. It didn't have rainbows in it like an oil slick, it looked more like powdered carbon or rubber. I have seen this in the past and it seemed to be associated with my impeller burning up. However, I ran the boat up to operating temperature and it stayed right where it was supposed to be after driving it for close to an hour. Oil pressure good, temp good, boat ran perfect in every respect.
Any thoughts as to what this black discharge may have been and whether I should worry?
04-30-2007, 04:34 PM
Not an engine guy, but could it have been fogging oil that was used during winterization. They spray in straight into the air intakes to keep everything from seiziing.
dunno but that's my guess...
04-30-2007, 04:37 PM
I would go ahead and pull that impeller and replace for peace of mind...
04-30-2007, 05:56 PM
That's what I'm thinking. I've never done it myself before, but it doesn't look too difficult, other than difficult to reach on the V-Dfirve.
04-30-2007, 06:00 PM
The black soot on the water was partially burned fuel resulting from a rich condition. If it happened on the first startup of the season, I definitely wouldn't worry about it. If it happens every time you start up, or if you get the black discharge every time you are at idle, then you have a problem that needs to be fixed. Running an engine too rich for an extended time will cause the cylinders to wear prematurely, and sometimes will cause dilution of the oil with gas that leaks past the piston rings. If, as you said, it runs fine while after initial startup, then that's probably not the case.