Leaking Fuel Tank

Made the discovery today that nobody wants to make – I am the proud owner of a leaking fuel tank.

At this point, the tank is still in place, so I don’t have details. It is verifiably leaking – oozing may be a more descriptive term. In any case, fuel is leaving the tank at a slow rate, but enough to discolor nearby FG and leave an odor trace. There is no doubt that there’s a leak. The clue was odor.

The tank is 16x32x66 (inches) or ≈ 147 USG. 16x32 is the plan area. Welded aluminum. The tank sits on an unknown base material and/or a FG base. All of the tank restraints are either steel with (by appearance) neoprene pads to prevent direct contact with the tank or wood.

The very good news is that the tank can be removed from the boat through existing openings – this is not a SawsAll job. Thank you, Viking.

The other pertinent info is that I’m an old guy who has a son that loves this boat. I kick, he gets it. Anything I do, I want to last beyond my likely time horizon.

Several questions for the TF gurus:

1. I always thought that aluminum tanks were borderline bulletproof, barring galvanic corrosion. What the hell happened?

2. It is obvious that my choices are to repair or replace the tank.

3. If replace – with what?

4. If repair – several options come to mind. This is not an expedition boat. It is and will remain a weekend, week at the islands, afternoon and evening cruise boat. 300 NM is a long haul for me. This becomes pertinent as these tanks gage at ≈ 4.6 USG per vertical inch. So I could lose a few inches in depth (gallons) without crippling the boat’s intended use. Several thoughts –

a. Clip a bottom inch or two and install a new tank floor.

b. Leave it as it is and weld a new bottom plate over the damaged bottom (assuming the leak is in the bottom and does not extend to the sidewalls).

c. The tank lower elevation/bottom (apparently) failed. If I repair the tank bottom/lower reaches, am I simply setting up for a new failure at a different (higher) location in the old (original) tank material?

5. Reinstall – what provisions/precautions should I take? Set base on neoprene, provide neoprene “insulating” material between structural elements and tank shell. Anything else?

6. I'm very clear as to the potential hazards and apporpriate procedures associated with hot work on a fuel tank.

As always, your time and effort in responding is greatly appreciated.

I'm a fan of if you're going through the trouble of pulling the tank whole just have a new one ready to slide back in same day. Most people don't like my fuel tank material of choice, steel.

"a. Clip a bottom inch or two and install a new tank floor. "

If you cut off the floor, then you can examine the walls. If the walls are good, then weld on a new floor then you do need to pressure test. I would just cut a half inch up. Point is maybe the bottom sat on a wet surface, so then only the bottom is corroded from the outside. Truth is, if you see obvious corrosion on the outside bottom in only one spot, maybe cut out only the bad section only, no need to replace the entire bottom if nothing is wrong.

Greetings,
Mr. 22. IF, as you say, the tank is easily removable What I would do is have it coated, inside and out. Thin sections can be reinforced with a proprietary fabric from the outside and incorporated into the outside coating. I'm pretty sure this is a very common solution with gasoline tanks (cars/trucks).

As far as re-bedding...I'll leave that to others to suggest.

Just had a tank repaired after doing a replacement 8yrs ago. Leak was at a welded area and the welder had a hard time trying to seal it. After half a day he still could not seal the leak.He finally had to take it to his shop for a cutout and plating the area after cutting the area out.This was done outside the boat. After talking to several welders fuel will commtamiate the crack /leaking area and make it very hard to seal the leak. If you are going to pull the tank,I would replace with a new tank. Like my guy said, it will leak again,but I don't know when.

Its just aluminum, repairing it is not rocket science. Have a good welding shop that you trust give you there opinion, after a good inspection. If it just has poltice corrosion in one spot, cut it out and weld in a patch. Standard procedure. If it has electrolisis damage and shows signs of multiple thin spots replacement "may" be in order. More likely just put a new bottom in, for about 1/4 of the cost of a new tank. DO NOT FALL FOR THE COATINGS OR PUT IN PLASTIC ARGUMENTS. That only comes from owners that wont pony up and do it right. Usually because its to difficult (read expensive). When you go back in with the tank follow Gerr's instructions to the letter. Epoxy coat the outside (I use coal tar epoxy) and glue the neoprene isolation strips to the tank with 3M 7200. A properly installed and maintained aluminum tank will last indefinitely.

Plastic fuel boxes came in a variety of sizes , they mount differently but solve the dissolving or welding hassles.

5. Reinstall – what provisions/precautions should I take? Set base on neoprene, provide neoprene “insulating” material between structural elements and tank shell. Anything else?

I would coat the exterior bottom with a polyurethane, such as Loctite's Black PL S30
For a more uniform coat, cut yourself a notched plastic trowel, put on some ribbons, let it cure a day, then go over that with a smooth trowel. This stuff will stick well to aluminum, and is 100% waterproof.
If you want the rubber super tough, mix in 30 to 40% 1/32 fiberglass milled fibers, turns into a rubber like on a car tire.

Loctite PL S30 Polyurethane Roof & Flashing Sealant from Loctite Adhesives

This stuff also works underwater.

Nothing complicated here, put in a new proper alloy Al tank. Insure the builder knows the correct marine alloy, fittings and rod to use. Viking can guide you to that tank builder as well as best install techniques.

Be careful with advice from strangers, me included. Al tanks are not a forever solution, yours made it 40 years through several potential abusive situations. Today's Al tank knowledge, if utilized, should allow a +50 year life.

I agree with those that say replace. We have marine tank builders in our area, pull tank, drop off and they will make it exactly the same within a week. DONE!

the labor will be the big part of the job. The difference between a new bottom and new tank probably wont be a big part of the job

First, my appreciation to everyone who took the time to respond. Second, understand about the advice from "strangers" - however, several of the folks responding have saved my rookie bacon more than once through their generous and thoughtful advice. I will proceed cautiously.

I've already received a quote on a new 5052 (?) Al replacement of exact dimensions - $1500 + freight. Dunno the freight yet. That at least gives me an order of magnitude basis for evaluating the repair option $.

Kulas44 - your reference to "Gerr's instructions" - as in Gerr the naval architect? Please clarify. Also, "3M 7200" - 5200?

RT - well, not "easily" but better than major surgery.

FF - checking the plastic option.

Sbu, you might check with Aluma-marine fabricators in N.O. They're in our backyard and do nothing but tank/boat fab. Might be able to fix or replace quickly with no freight charges. With oil field service down to almost zero they might be looking for work! Labor to remove and replace will far exceed the cost of your tank.
If you can get that tank out without much hassle I would replace it in a heart beat. Went through that last summer...bit the bullet and replaced both steel tanks.

That's Aluma Marine in Harvey? I'm calling them right now - thanks. Called a couple of places down here that I know from industrial work - they didn't want to hear anything after "rec boat". Did they do your replacements?

Check in the back of fishing mags, our local weekly has a bunch of guys listed, look at a tackle shop for one, better if you can drop off old one to be copied. Also now is the time to assess where the sender gets mounted, had mine moved for easier accessibility also has a manual gauge you can read right on top of it.

I had Seabrook Marine remove/install new tanks that were fabricated in Harvey. Plenty of fabricating shops that can do your work in your area. I feel for ya!


Oh, and really hate to say this, but I would have your other tank inspected as well. Might be time to just bite the bullet and have both tanks replaced....sorry to bring this up on a Monday morning.

I'm sure I don't yet fully appreciate the labor component. I've got to hand it to Viking - it looks like they actually considered this situation. I've had several blow boats where any major component removal amounted to cutting door size holes in FG.

My perspective is that if one is leaking (barring some unique physical damage) the other (identical configuration mounted cheek by jowl with the leaker) is probably ready to go, too. So, whatever the fix is, I'm looking at both.

Dave Gerr goes into great detail about tank installation in his book "boat owners mechanical and electrical" IIRC or similar. 3M 7200 is the next step past 5200, horrible stuff. Sets up harder than 5200. Just another "small" thing that most folks here have never heard of. That list is long.

Didn't know about Gerr - have Calder. Anyway, thanks, I'll run it down.

I may have mis spoke. IIRC Gerr's book covers only mechanical aspects and not electrical. Calders covers electrical also. Anyway, one of them has a good section on aluminum tank installation. CRS (cant remember $hit)

kulas44 said:

Dave Gerr goes into great detail about tank installation in his book "boat owners mechanical and electrical" IIRC or similar. 3M 7200 is the next step past 5200, horrible stuff. Sets up harder than 5200. Just another "small" thing that most folks here have never heard of. That list is long.

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Hmm... I guess I'm one of those folks that has never heard of either of those two "small" things. Gere's book by that name nor 3M 7200.

I've heard of 3M 740 and 760 but never 7200. Can you post a link?

Ok, I did say I mis spoke, so the book is By Dave Gerr, Boat Mechanical Systems Handbook. Concerning tank coatings p. 85, under the heading of Aluminum Tank Preservation. As for 3M 7200, I cant find a thing. Its been at least 10 years since I used any (if that was in fact 3M 7200) and I think I got it at West Marine in Galveston Tx. I re gooped some salon windows with it. Lately I have been using Window Weld polyurethane when I need a permanent "stick". Mostly because of availability. For the tank/neoprene application 5200 would be ok.

Just musing here but I wonder if something like Rhino Liner spray truck bed coating would be ok. It tough as heck to stand up to the abuse some of it sees in pickup truck beds.

Just as long as the prep. is done.



I'll look up Dave Gerr's book. I don't have them all clearly, even though I thought I did.

I have used truck bedliner on a couple of aluminum boats. No primer, just straight to the clean metal. It takes a beating pretty good. Metal prep is important. Rougher is better, and etch with acid. I like ExtremeLiner sold on ebay. Its a 2 part polyurethane. Comes with instructions and spray gun. For a tank I would use the finest rubber granules. I know you dont really need nonskid on a fuel tank, but the rubber is a big part of why this type of polyurethane is so tuff. And it looks good.

And like older powder coatings...I have seen thousands of examples of both fail. Boh in truck beds and aluminum boats. Once one tiny part fails...it seems to spread faster than the most horrible cancer can.

While both can work like majic...it has never seemed like the majority to me though.

I have good experiences using the Loctite PL S30 on all kinds of metal, wood, fiberglass.
It is a softer rubber than 5200 and a lot cheaper to buy. A couple times had some issues sticking to select spots on pine wood, which when I peeled off some of it, there was pine sap, so surface contamination prevented the adhering. PL S30 is designed for exposure to hot sun, the rain, made to stick to wood and metal on roofs.

I found it also sticks underwater on the boat. I have also sealed up several through hulls using it.

I also repaired a 3 inch ripped rubber exhaust hose end. I mixed up PL s30 with 1/32 " milled fibers, smeared it on an acetone cleaned hose and into the tear. Then wrapped several overlapping layers of FG wall board tape going down the hose 4 inches, fully saturating the FG tape.
Then smeared on a top layer. Waited 2 days, and was like a new hose.
This hose originally tore when it was stuck and I had a very hard time getting it off.
So now I use Rector seal T plus 2 on all the hose and fittings.

ps is correct, lots of bad looking jobs out there. Aluminum can be the most difficult to coat. I will say that I've never had a problem with coal tar epoxy on an al tank. It may be the only thing nastier than 5200. And, it aint cheap. Spraying is not really an option and after roller/brush application it looks like it was rolled and brushed. If you want a lifetime tank it does work. And its proven.

We are having a similar problem. We just found a slow leak at the weld of the starboard diesel tank and the connector to a shutoff valve - luckily just before we were supposed to launch yesterday. We are now pumping out many gallons of fuel, then the discussion of whether a repair is possible or how to get the 325 gallon tank out (and probably the port one as well ... 30 year old black steel). Cut the tank up? cut into the fiberglass side of the boat? and looking for skilled personel/marina/boat yard on the US side of Lake Ontario near Point Breeze and Rochester....

I wish our tanks could come out easily as it appears yours will!!

Delia, when I changed both tanks 8 yes ago,I had a A frame set up in the sallon moved motors to floor level,cut tank up threw out the door. New tanks had to be smaller to fit through rear salloon window. I can do most of my work so labor was low. Just had to do it again as weld started leaking,weld was contaminated and fuel weaken weld . This time
I had a crane/Pettibone lift come through the port window and the tank was removed thru the starboard window. Engine was lifted to floor level ,tank was removed ,easy access once engine out of way then engine back on stringers as tank was repaired. Then repeated to put tank back in. Don't wish it task to anyone, but it can be done,with carefully planning,knowledge of what needs to be done,and plenty of beer. Good luck!!!

kulas44 said:

I will say that I've never had a problem with coal tar epoxy on an al tank. It may be the only thing nastier than 5200. And, it aint cheap. Spraying is not really an option and after roller/brush application it looks like it was rolled and brushed. If you want a lifetime tank it does work. And its proven.

Click to expand...

I will vouch for the coal tar. It has heavy solids and does not get pinholes in it. It's the pinholes that kill a coating.