Fuel tank leak or loose fuel sending unit?

[Juan]

Hi guys,

I wonder if you can help me with this one: I went to sleep on the boat on Friday night. Everything was fine. On Saturday evening I filling up the tank and after a couple of hours we went to sleep I smelt diesel, so I check the fuel tank I found that a small trace of diesel was running from the fuel tank down below the head sink to the bilge. So I took out the panel that covers the fuel tank (on the port side) and I found this at the bottom of the tank...(see picture). It was like touching grease but it smelled like diesel. Here is another picture (second picture).  It is obviously something that has been building up there. So my immediate reaction was, maybe I have a very tiny whole at the bottom of the fuel tank. But then, I realize that I didn't smell diesel on the night before. It was only after we fill up the tank to the top. So then I touched the fuel sending unit and it has diesel around (see picture). So my second theory is that this unit has been loose and so when I filled the tank to the top, diesel has been spilling from them and gravity sends the diesel to the corner of the tank where you see the build up (first picture).

Obviously I cleaned everything, I tighten the screw at the top of the fuel sending unit (it was indeed loose), I ran the engine for a couple of hours to lower the fuel level and now I will wait until tomorrow to see if the diesel trace will reappear or not. In the meanwhile, I wanted to check if anybody has gone through a similar experience.

Thanks,

Juan 

[Ed Shankle]

Coincidentally, I just had a similar experience, only my fill was done in the fall, as part of winterizing. Found some diesel in the bilge this spring and traced it back to the sender on the tank top. This was before launching for the season. I pumped out a few gallons of fuel after the cleanup and haven't seen anymore leaking. I keep a wrap of "diesel diaper" around the tank fittings as a means of monitoring it. That's why it was easy to trace the leak originally.
I'm assuming that I filled too close to max and that expansion due to spring temperatures caused the leak. I also think, but haven't confirmed yet, that the overflow vent must either be clogged or the hose to it is looped enough to prevent the expansion from dribbling out of the vent. I snugged the sender screws, but none were loose. I'll just need to be careful to not overfill in the future. I also plan to add an expansion bowl to the vent line as an added measure. If it still leaks from the sender, I'll need to rebed with a diesel tolerant gasket forming sealant.

Regards,
Ed