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Gas Odor in bilge of 2009 Sun Deck (20' OB)

bsmith Member Posts: 2
I saw old postings on this subject, but they were closed (answers not available).

My boat is 2009 Sun Deck 20' outboard used in fresh water only. I purchased it used in 2018 in near perfect condition. No problems from 2018 - 2021, but just now I have started smelling gas fumes in bilge and other enclosed areas. The odor is strong. When I ventilate with a large fan by blowing air into the console opening (all other hatches open), the odor goes away quickly (3-5 mins), then slowly comes back (30+ min of operation, or just sitting overnight). Ventilating for a long time (multiple tries of 24 - 36 hours) does not stop it from coming back. I inspected as much as I could, wiped around with rag, etc, but I could not find any liquid gasoline in the bilge. When I wipe with a rag, the rag soaks up very small amounts of water that are present, but the rag does not smell like gasoline at all. I couldn't find any leaks around fittings, but it's a pain to see in there - and I do not really know where to look. I normally keep the gas tank completely full, but I was thinking that the filler hose might be leaking, so I am running the gas down to lower level in the tank (now 1/2 to 3/4 full), but the odor still persists. A very reliable and reputable local marina checked it out and said that they could find no gasoline leak.

I do not what to try next ... I am thinking of several possibilities ... here are some questions.

1 - How can I get a diagram of the fuel system for this boat so I'll know where to look?

2 - Flush out the bilge by running water through from the front (anchor hatch) and out the drain plug and/or bilge pump in the back. Maybe there's a small amount of liquid gas somewhere that I can not see?

3 - Add some fluorescent (optical brightener) material to the gas tank and search for leaks with UV black light. There are several types of these optical materials readily available. Which ones of these work best? Will these foul the plugs, fuel filters, gas/water separator, etc in my Yamaha 150 outboard? To do this I'll need a diagram of the fuel system so I'll know where to look.

4 - Install a gasoline vapor monitor and a blower to continuously ventilate the bilge. But this just treat the symptom, not the problem.

Thanks for any help.