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Discussion Starter #1
Hello,
I'm installing a new aluminum fuel tank in our 1984 Sabre 34.

First, should I paint the tank? The old tank was painted, but I'm under the impression that this should not be necessary. There was no external corrosion on the old tank, although again, it was painted.

Second, the original tank has an anti-siphon valve in the diesel supply line out of the tank. Is this required by ABYC for diesels? It's working OK, but seems like one more thing that could go wrong.

Thanks for your help!
-J
 

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Hi. My advice is to on no account paint the tank. Far from protecting, it can encourage corrosion. As long as the tank remains away from standing water in a ventilated area the bare aluminum is the best protection. With regards to the anti-syphon valve I am unsure if it is an ABYC rule for diesels but it would certainly make sense as syphoning a tank full of diesel into the bilge only to have the bilge pump throw it overboard could prove very expensive in fines should it be noticed. My advice is to leave it.
 

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Discussion Starter #3
Thanks KMC. I think not painting the tank seems to be the general consensus and how I'll go too.

As for the anti-siphon, I've heard but cannot confirm that it's a requirement only for gasoline, and that many diesel systems do not use one. Also that the benefits are outweighed by the drawbacks (potential point of clogging, failure, makes the fuel pump work harder, etc). However, my experience in this is from reading and I could be completely wrong. And I see your point too.

Anyone have info on ABYC and/or Coast Guard requirements on this?
 

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I replaced my two 55 gal steel tanks with aluminum tanks about 14 years ago. I agree with the comments about not painting and not installing the anti-siphon loop. I would add that it's a good practice to secure the tank with good ventilation outside and beneath the tanks. My tanks are sitting on starboard runners that are fastened with screw heads well reccessed and not other metals fixed to the tanks; however, there are tabs welded to the tanks that are then securely fastened.
 

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Discussion Starter #5
...I agree with the comments about not painting and not installing the anti-siphon loop...
Hi CaptainForce. Thanks for the comments. One point of clarification is that we're referring to an in-line anti-siphon fitting as opposed to a loop. It looks something like this one below, though not identical. Same idea though.

Is your advice still the same?
Thanks again,
J

 

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I did say, "loop". I think I just type this by rote after "anti-siphon"; however, what you present in the photo is the same item that was formerly within my diesel pick up lines from my tank. I drilled out the balls inside these one-way valves. For the first year after the install of my new tanks I was able to run well on one tank, but the other would often cause my engine to stall after about twenty minutes of running at 2500rpm. I've heard of others having problems with these valves sticking and I did not want the insecurity of having my fuel supply blocked at some innappropriate time,- like breaking an inlet at the rocky jetties!

I should add that the one tank pick-up never stuck and many may never experience a problem. I guess there may be different qualities of the production of these valves.
 

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Discussion Starter #7
Thanks CaptainForce. I thought that might be the case, but wanted to be sure.
 

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Nix the painting. I do tank inspections in my day job (API licensed inspector) and I've seen many Al tanks ruined by coatings.

The 2 big rules are to keep the base out of saltwater, and be VERY careful with dissimilar metals (no brass or bronze fittings, only SS by code) and grounds. Additionally, there are some additives that greatly reduce Al corrosion. Practical Sailor did a review. As I recall Stabil and Star Tron did best. However, internal corrosion is mostly a steel tank problem.
 

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Discussion Starter #9
Thanks pdqaltair. When you're referring to fittings, you're referring to the pickup and return lines, correct? They are SS, I believe. But the fittings that attach to those SS pieces might be something else. Is that the no-no? Or are we mainly talking about what comes in contact with the tank?
 

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On the subject if fuel tanks, we just discovered our catalina 309 (2008 year) tank is corroided on the bottom. We are shocked that a six year old well kept boat would have this problem and we are baffled how moisture may have gotten into the space.
 

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On the subject if fuel tanks, we just discovered our catalina 309 (2008 year) tank is corroided on the bottom. We are shocked that a six year old well kept boat would have this problem and we are baffled how moisture may have gotten into the space.
Please clarify for us if this was an aluminum tank and the nature of the bottom surface. Was it flush with wood, fiberglass, on runners or otherwise ventilated.
 

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Freedom 39
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Within a two week period both of my aluminum fuel tanks started leaking. The tanks both had corrosion in the bottom in an area I will call a "sump" for lack of better terms. The rest of the interior and exterior of the tanks is pristine. The tanks are about 30 years old. The tanks hang from tabs welded along the top and corroded from the inside out.
 

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I understnd the risk of the corrosion of aluminum tanks next to a hull that gathers moisture from condensation or at wet bottom surfaces without good ventilation. I would be concerned about corrosion from the bottom inside the tank and wonder about the cause; however, I'm not sure how one determines that the corrosion originates from inside the tank. I'd like to hear the method that would be used to determine wether the corrosion begins on the inside or outside and also, what thoughts knowledgeble people might have about additives in diesel fuel that might corrode aluminum.
 

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Freedom 39
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In my case the aluminum sump was cut off and the inspection port on the top removed. The inside of the tank where the leak was looked like a termite/acid ate away an area approximately 3/8" in diameter from the inside. The outside of the tank looked like a tiny crack. The exterior surface was flush. It was pretty obvious even if my description isn't clear.
 

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............. The inside of the tank where the leak was looked like a termite/acid ate away an area approximately 3/8" in diameter from the inside. The outside of the tank looked like a tiny crack. The exterior surface was flush. It was pretty obvious even if my description isn't clear.
No, this is clear and well said. I think the thought that the inside of the tank having a larger surface area of corrosion than the outside would be compelling evidence.
 

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Freedom 39
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After cleaning up the tank, I will call it tank #2, and seeing that many areas had very deep corrosion and pitting on the interior, I went ahead and ordered a replacement from the original manufacturer. Since tank #2 seemed to have more water and crud in it than fuel and still managed to last 30yrs, I figured a new one will last at least that long with some minor attention.
 

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There's a good article somewhere on the net on how to install an aluminum tank. Basically, DON'T let it sit on a surface - use non-metallic, non-absorbing (read plastic) strips to allow air circulation. And don't paint it. Basically avoid anything that would allow moisture to attack the tank.

As for the anti-siphon valve, I can't see why you'd need it and as you say, it's one more thing to go wrong. What you DON'T want is an airleak anywhere in the fuel intake.

druid
 
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