Gas tank in a gas tank

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bonro001

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Jun 25, 2013
Messages
7
Hello all,

Wanted to run this by the group to make sure I am not crazy. (OK, won't prove that but here goes)

I have a caravelle 209 that I recently replaced the floor. At some point after a good rain my gas tank filled with water, so I must have nicked it somewhere. (it's a poly tank)

Anyway, have not been able to remove the tank, it is glued down pretty solid. So today is when I had the idea. I want a smaller tank, and found one that would fit inside if I remove the top of the existing tank. I have drained the tank, filled it with water and drained it again to remove all the fumes and plan on cutting the top off, then placing the new tank in the old tank.

To fill in the space, plan on using marine foam, the type you mix, to fill in the gap, then replace the floor and carpet.

Anything I am missing in my plan? Anything to watch out for?

Thanks in advance!

Rob
 
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UncleWillie

Captain
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Oct 18, 2011
Messages
3,995
Re: Gas tank in a gas tank

Two parts sound questionable;

The part where you think you have a hole in the tank that doesn't Leak fuel OUT, but leaks water IN.

and the part where you said you wanted a SMALLER Gas tank! :confused:
 
Grub54891

Grub54891

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Jun 17, 2012
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Re: Gas tank in a gas tank

Are you sure your tank leaks? Do you smell fuel? Sometimes the filler will leak water in,but not fuel out. Unless you run with a nearly empty tank most of the time so the leak dosn't show up easily. Besides,a low tank invites condesation,maby you have no leak?I'd find the culprit before cutting it up,and poly tank's can be repaired if the problem is not to severe.
 
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airshot

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Re: Gas tank in a gas tank

OK..nothing wrong with your plan however the bigger problem I would be wanting solved is how the water got in the tank to begin with,
you could go thru a lot of trouble only to find you have the same problem again.
 
B

bonro001

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Jun 25, 2013
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Re: Gas tank in a gas tank

airshot said:
OK..nothing wrong with your plan however the bigger problem I would be wanting solved is how the water got in the tank to begin with,
you could go thru a lot of trouble only to find you have the same problem again.
Click to expand...

Agreed, have taken it to several shops, no one has any answers. I know that I had 1/4 a tank a week prior, it rained quite a bit, and then I put say 3 gallons in. (35 gallon tank) Next time, no start and the tech said that he could almost drink the gas there was so much water in it.

Now, I also have suspected vandalism, but for someone to put that much water in would take more than a hit and run type of thing.

So here I am, wanting to hit the lake, floor torn up and new carpet sitting in the wings. Thinking that a new tank is the quickest route to not having to lay yet another piece of carpet. As far as mysteries in my life, this is a biggie.

An for the comment on amount, yeah, we just use the boat here in Austin, usually don't cover more than 30 miles in a trip, so came up with the tank in a tank idea to eliminate the need to remove the old version.

And, might just be justifying here, but wow, better flame protection. (Yeah, stretching)
 
F

Fed

Commander
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Apr 1, 2010
Messages
2,457
Re: Gas tank in a gas tank

There's only a few places where the water can get in, find the leak & fix it.

Filler cap seal.
Filler cap skin fitting.
Fill hose at filler cap.
Vent fitting etc.
It's pretty simple really.
 
roscoe

roscoe

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21,878
Re: Gas tank in a gas tank

The pros I have talked with will tell you NOT to foam the new tank in.
Anchor it down, perhaps cushion it if it jiggles in place, but don't foam it in.
 
B

bonro001

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Joined
Jun 25, 2013
Messages
7
Re: Gas tank in a gas tank

roscoe said:
The pros I have talked with will tell you NOT to foam the new tank in.
Anchor it down, perhaps cushion it if it jiggles in place, but don't foam it in.
Click to expand...

Very good point, thank you. Will sure it up inside with some other material, and it saves me $$, that foam mix is pretty expensive.

Will also shoot some pictures.
 
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H

H20Rat

Vice Admiral
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Mar 8, 2009
Messages
5,204
Re: Gas tank in a gas tank

Something else is up... You don't get that much water in your tank from a leak, it simply isn't possible. Leaks cause gas to go out, they do NOT cause water to fill up your tank!

Where is the vent line connected? That would be the absolute first thing to check.
 
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airshot

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Re: Gas tank in a gas tank

If you have an external vent for your tank be sure and check to see if the vent line has a vertical loop in it....this keeps splash from going into the vent and into the tank. On some boats the vent line is replaced and the loop is not put in the line and you would be surprised how much water is forced into the vent line when the boat is underway and water is splashing up the sides. That is probably the most common, yet hard to find water intrusion I can think of.
 
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UncleWillie

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Re: Gas tank in a gas tank

bonro001 said:
Very good point, thank you. Will sure it up inside with some other material, and it saves me $$, that foam mix is pretty expensive...
Click to expand...

The price of the foam is not the issue.
The fuel tank can physically change size up to ~3% over Summer/Winter Temperature ranges.
Once the foam is set, it is surprisingly strong.
3% of 2 feet is 3/4 of an inch. Something would have to give. $$$
 
GA_Boater

GA_Boater

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Re: Gas tank in a gas tank

Isn't an under floor tank vented 100% of the time? So why would it expand 3%? I know my 5 gallon plastic portable expands in the heat and as soon as I open the vent to fill the mower, it poofs and back to normal size. If I leave the vent open, it doesn't swell.
 
Bob_VT

Bob_VT

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Re: Gas tank in a gas tank

One question........... are you going by the gauge for the fuel level or are you using a stick or some other way to measure? DO NOT trust the fuel gauge ;)
 
tpenfield

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Re: Gas tank in a gas tank

bonro001 said:
Hello all,

Wanted to run this by the group to make sure I am not crazy. (OK, won't prove that but here goes)

I have a caravelle 209 that I recently replaced the floor. At some point after a good rain my gas tank filled with water, so I must have nicked it somewhere. (it's a poly tank)

Rob
Click to expand...

Still not quite understanding the entire situation . . .


Gas tank "filled" as in totally or substantially full of water? sounds like yes . . .

You replaced the floor, yet water can still get below deck to the fuel tank? What else below deck might be holding water?

Aluminum tanks are often foamed in . . . poly tanks are usually fastened in.

Got any pictures to share?

It would probably be good to understand the water situation better, before deciding if your plan is a good approach.
 
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midcarolina

midcarolina

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Jul 16, 2013
Messages
631
Re: Gas tank in a gas tank

If I were you I would pressure test the gas tank, It's not a difficult thing to do........then you would know if the tank has a leak, and know for sure replacing tank will fix problem.......right now you are just guessing/hoping that will fix the problem.
 
NYBo

NYBo

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Oct 23, 2008
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Re: Gas tank in a gas tank

Yeah, something doesn't add up. A leak small enough to not be really obvious would have to be subjected to a tremendous flow of water for enough to get in to fill the tank. I would investigate more before condemning the current tank.
 
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