2000 Carver 404 - Gas Sheen While at Dock

[Reardon]

Good Morning Fellow Boaters

My neighbor (about 4 docks down) mentioned to me that he thought there was a "Gas Sheen" coming from my dock area. He noted a "small sheen" going past his dock (maybe 300-400 feet away). When I observe the water around my dock, to be honest I cant see anything obvious but maybe a few "streaks" that look like they could be a "gas sheen". The gas in water that I have seen in the past is pretty obvious. Glossy surface that often times has a multi colored sheen to it. In addition, my lake is not the cleanest and is very alge laden so not easy to distinguish things at times.

Assuming that there is/was a sheen (I am going to, because I tend to be pretty conservative about these types of issues and want to make sure they are addressed), any thoughts on what could cause that? A few facts that might be helpful:

* The boat had not been run for over 48 hours when he reported seeing the "sheen". Basically, if there is fuel getting in the water, it is doing so when the boat is not in any type of operation and the engines had been cold for two days.
* I have a starboard, port and auxiliary tank. Since I last fueled, I have been running off the port and starboard tanks and they are at about 2/3rds full. The Auxiliary is still completely full (btw - when I bought the boat, the previous owner told me to use the auxiliary tank first, which I am not doing after my last fill up...never understood why he suggested this..maybe related?)

I do have one theory, which is that the Auxiliary tank, being completely full has leaked some fuel through it's overflow valve? When I check the valve, it does not appear to have any fresh fuel around it, but it has been a very hot weekend here in MI and thought if the tank was topped off, maybe the valve was releasing.

Any thoughts would be great.

Thanks
Rich

[hausherrs]

Do you smell fuel while inside the boat? Outside?

Maybe he overfilled the aux tank and suggested running it first to get it down a little??

[mjk1040]

If the auxiliary tank is completely full and the temp was a hot one I would say it's coming out the vent for that tank. Happened to me last fall while putting the boat away. Run the engines on the auxiliary tank and the previous owner was correct, you should rotate your fuel and use up that older fuel first and put it up in the winter with fresher fuel. BTW I had to take about 2.5 to 3.0 gallons out of each full tank to get the fuel from expanding and coming out of the tank vents. You want to put your boat away in the winter with the tanks as full as possible to prevent condensation in the tanks in the winter.
Mike

[AaHubb]

Another possible source is a bilge pump running. If you have a fuel tank leak guess where it goes!
..Aaron

[Viper]

The above are all typical possibilities and should be checked in case this is actually fuel in the water. Also consider though that in certain water types/conditions, you'll get a film on the surface that may simply be a by-product of decomposing organic matter. Doesn't look exactly like fuel but it's the default assumption. We get it often in our area and it's always a panic as folks' first reaction is that someone is leaking fuel.

[Viper]

Source of the post.....You want to put your boat away in the winter with the tanks as full as possible to prevent condensation in the tanks in the winter....

I think the school's still out on that. This was the case "old school" however the debate now is whether you take on more water through the process of condensation or as a result of the ethanol in the fuel now. The ethanol (alcohol) in the fuel will suck the moisture out of the air anyway and suspend it in the fuel. The more ethanol fuel you have, the more water you'll have in your tanks 6 months later. Was bad enough at 10% ethanol, with some areas moving to 15% I imagine will get even worse. Of course if you aren't using ethanol fuel in your area then no worries about having full tanks. But this is a discussion for another thread!

[mjk1040]

Viper;
I agree, in our area we have non ethanol fuel, and hopefully that's all I put in my tanks, thus my statement. However if you are boating in an area that only has ethanol fuel, I agree with your statements. If I was in an ethanol fuel area and had only that type of fuel, I too would run them down as far as possible, ethanol fuel most generally shouldn't be stored for more than 30 days they say and sure does pull in moisture. SEA FOAM! Mike