Sheen from exhaust

[RicM]

This is my first diesel, so I'm still figuring it out. How much "sheen" do others see in the water from their exhuast when the engine is shut down? I came in this afternoon from my first day of fishing (one slightly undersized bass) and when I killed the engine at the dock there was about a 4 sq foot sheen of petroleum of some type coming out of the side exhaust. I have the 315 Yanmar engine with 340 hours on it. I ran hard coming in (3200 RPM for 20 minutes) and idled in for 12 minutes from the breakwater to the slip (no wake zone). Should this be a concern or is normal for a diesel? I realize there must be some petrochemicals in the exhaust.

[Capt Paul]

Ric,

I get this from time to time, I especially see it in the cooler weather out here in the left coast at engine startup . I also see it sometimes after I have to use a hard reverse burst to turn the boat into the slip. Not sure what that means but I think you are seeing something that is considered normal.

Paul

[Cape Codder]

Ric,
Funny you should mention this, as I was about to write the same thing.
Yesterday, while at my mooring, just after I shut down, I too noticed a slight sheen near the exhaust port.
I didn't know if this was normal. Sounds like it's normal for the Yanmar 315 anyway.

[Denis]

I was very nervous my first year with this boat, after I noticed the same sheen from my exhaust. I have the 300 Peninsular, it runs very strong, burns clean and sounds fine. If it aint broke I not messing around with it.

[jcollins]

I never notice it. But, by the time I shut down I am busy getting the wife and dogs off the boat. I'll pay attention next weekend. However, I do take a look to check at start up. Never have seen it.

[Mariner]

It's common to see just a little bit of a thin sheen. What you're seeing is fuel residue from the exhaust. A very small amount of unburned fuel that has accumulated in the exhaust, trapped in the soot, can create a surprisingly large sheen when you slow down and the exhaust is resubmerged and water sets it free. The mention of it being more noticable after hard backing down only supports this, as water being forced into the exhaust would just dislodge more soot.

Again, it's an extremely small amount of fuel, not even actually measurable, absorbed into the soot that naturally lines the exhaust. Now, if you see a thicker sheen similar to what you would see if you were to actually pour a cup or two of diesel into the water, then you have cause for concern. But a four foot wide sheen is equivalent to about one drop of fuel.