Gas Odor in Bilge

[Bduck]

I have a faint or light gas smell in my bilge. It has always been there, but I was unable to locate any leaks. I have used a dye to put in the tank which takes a black light to check if penetration at fittings or tank itself coming up with no clues of visual leaks. I even went to the point of replacing sender unit gasket and rechecking fittings for proper sealing & tightness. This is what I found researching on another forum:

Permanent Fuel Tanks
OPERATINGTEMPERATURES
Moeller Marine fuel tanks are capable of operation within an ambient temperature range from -40°F (-40° C) to 176°F (80°C).
IMPORTANT: Fuel tanks temperatures must be limited to 150°F (66° C) when not in operation. Processes that include dry heating
of the fuel tank beyond 150°F (66° C) should be discontinued immediately. Fuel tanks subjected to temperatures in excess of
150°F (66° C) when not in operation, could be considered as damaged, and may not be covered under the limited warranty.
PERMEATION
Permeation is a natural phenomenon of gasoline in a cross-linked polyethylene fuel tank.
Permeation is the result of gasoline fumes escaping from the fuel tank, not the loss of liquid fuel.
Several precautions need to be addressed when using across-linked polyethylene fuel tank:
– Fuel(gasoline) vapors settle to the lowest point in the compartment, therefore, a means for removing the fumes is required.
See ABYC Standards Section H-2 for specifics.
– A covered boat will not allow these fumes to escape, so buildup of these fumes is inevitable. Caution should be taken
when a boats fuel tank contains fuel and is covered for an extended period of time. A boat cover should never cover
the fuel tanks exterior vent fitting(s).
– Fuel vapors will migrate to any compartment open to the fuel tank. The smell of fuel vapors does not necessarily
mean that there is a leak in the fuel tank, but a closer inspection should be performed.
– Fuel vapors may be absorbed by other objects located in compartments where fuel vapor may migrate.
Following the above precautions, across-linked polyethylene fuel tank will provide years of service.


https://webstore.ansi.org/preview-pages/...ew_H-2.pdf

Permeation, involves pollutants such as gasoline that can seep from groundwater or soils through the walls of plastic pipes, which has been noted in reports by the Environmental Protection Agency and the Water Research Foundation (formerly the Awwa Research Foundation)

[wiperhunter2]

I think this is normal for most boats, I can't speak for all boats but my last two boats, that have internal tanks, I have smelled this, especially when I open up certain compartments, around the fuel tank.

[LundLefty]

I/O or outboard?  I/O bilges and engine compartments always seem to smell faintly of gas.  Did concern me a bit on the I/Os we've owned, but I was always diligent about running the blower prior to start-up.

[Bduck]

My boat has outboards but internal 60gal fuel tank bilge mounted; no blower equipped. I used to have an IO with blower, IO engines provide an ignition source and an additional fuel/vapor source.