Aluminum gas tank question

[BrokeBoatMI]

Can anyone tell me wth happened to this gas tank? This off season I decided to remove it smelling strong fumes late in the year. I took it out and it looks like this. I’m planning on replacing with a plastic tank of similar size, but not sure if I’ve fixed the root cause.

I pressure tested the tank using some rubber stoppers and an air gauge; I couldn’t get it to pressure up so I expected to find some holes in the bottom of the tank, but nothing. Also noticed some fuel in the bilge late in the year.

The boat is a 1992 Thompson, so just cutting out a floor area and patching back with the proper plywood and some fiberglass work. The rest of the floor seems to be in very good shape, as was the floor above the tank before I cut it out

 

[airshot]

Your aluminum tank has corroded, probably some pinholes from the corrosion. Aluminum oxidises naturally but very slow !! Something has sped up the corrosion on your tank. Could be caused by a variety of things such as.....excess moisture wherevthe aluminum never was allowed to dry out, chemicals from cleaning (bilge cleaners), corrosion reactions from what ever the tank set on. Is itbused around salt water?? Moving to a plastic would be a better move unless you can identify and remove the corrosion issues. My boat had an aluminum tank installed about 15 years back and it still looks like new, but it has not been subjected to salt water or any other corrosion causing issues.

 

[Scott Danforth]

your 1992 boat was designed to last 15 years

its now 32 years old

The boat is a 1992 Thompson, so just cutting out a floor area and patching back

you will find you have wet foam and probably rotting stringers and transom. the floor is the last thing to rot. since you are addressing a soft spot in the floor, your transom, foam and stringers have long ago gotten wet and started to rot

the damage on your tank is corrosion from being in contact with moisture and minerals.

if the green bonding wire was not attached, it would have corroded much much faster.

 

[BrokeBoatMI]

I didn’t find any foam around the tank, it was actually suspended above the fiberglass by the four aluminum tabs on top of the tank. I do see some yellow foam on the other side of the stingers that seems intact.

I’m not sure if how these stringers look is acceptable, it seems dry but I’m no expert. The black spot in the middle is tar like, solid below and can wipe off, maybe where same gas was sitting for some time.

 

[airshot]

Pics wont tell the story, an actual sample of the wood is needed. Transom and stringer wood sample, or if they are really bad, a simple pocket knife stab will tell the story. If you can push the point of a pocket knife into the wood....they are rotted.

 

[jeffrey.bean]

I didn’t find any foam around the tank, it was actually suspended above the fiberglass by the four aluminum tabs on top of the tank. I do see some yellow foam on the other side of the stingers that seems intact.

I’m not sure if how these stringers look is acceptable, it seems dry but I’m no expert. The black spot in the middle is tar like, solid below and can wipe off, maybe where same gas was sitting for some time.View attachment 375056View attachment 375057View attachment 375058View attachment 375059

Us a 1/4” drill bit, and drill a few test holes. If the wood comes out dry and yellowish, your good, fill with PB. If it’s black and wet, break out the sawzall and grinder

 

[tpenfield]

As stated, corrosion. It looks like there was moisture in the contact areas of the underside of the tank. Aluminum does not like long-term contact with water.

As mentioned, at 30+ years of age it is ready for a new one.