Aluminium diesel tank with bronze elbo and copper pick up tube. Corrosion potential?

[Eastward ho 24]

This weekend I decided that since I have the sole out of my new ( new to me) boat it’s a 1977 downEaster 32 , that the diesel tanke were probably never cleaned out since there was no access plates and the tanks original. I originally polished the fuel recirculating it for hours through a 10 micron seperator and filter but the fuel just didn’t look right. So alas I made my own deck plates similar to the sea built ones. I used an aluminium cover and an aluminium doubler plate for the inside. With gaskets on both sides. I used rubber tire inner tubes for the gasket. A brief description of the process here in case any one wants to duplicate it themselves. Total cost was 100$ to 200$. I did a 10” hole. Basically you just make (2) 10” plates ones the cover the other I cut an 8” hole out of for the inside doubler plate. get them in a vice or clamps and drill holes every 2” around the perimeter for the through bolts. Once that’s done number the holes and put the cover aside. For The inside doubler plate I threaded 1/4 holes into it and used 1/4” ss hex bolts and threaded them in very tightly so when tightening down from the top they wouldn’t back out. I used the loctite red permanent thread locker on a test piece but it seems to be a useless product. After sitting over night i tested it by removing the bolts and the thread lock did absolutely nothing at all. Don’t know if I got a bad batch or dissimilar metals had any thing to do with it, but for me was a totally useless product. Any how...after you thread them in tight put the cover back on and be sure it’s a nice and tight fit. If not make it fit perfectly. Use the doubler plate as your cut out template( be sure to locate baffles!!)and be sure to number all the holes and what side is up and down and fit your gasket of choice. Now cut the doubler plate in half so you can sliderold it in half and slide it inside the tank. I think you guys got the rest.........

Now my questions are i used ss bolts disimmaler metals I know. However since ss is commonly used on aluminium spars etc figured it'll be ok? With out double checking I believe ss is closer on the galvanic scale then say brass bronze and copper. Which leads me to my second questions; the old pickup tube was aluminium tube down to the lowest point of the tank and was clogged and broken off so I removed it and trashed it. Looks like the P.O. got a 3/8 bronze 90 and soldered a copper tube to the inside of it, slipped that into the tank and threaded it in and it works. But the tanks are buried in the structure and I intend in keeping the boat a long time and doing serious cruising and a tank failure will be a catastrophic problem. So from my understanding bronze brass and copper are far enough away from aluminum on the galvanic scale that the bronze elbow and brass pick up tube will be a problem down the road. Am I correct in this assumption? On a side bar when ever inquiring about raw water, through hulls,or submerged metals, the marine stores seem to insist brass to bronze is ok, and brass and ss is fine in seawater. The industrial fishing boat fleet supply house uses it on all commercial fishing vessels. And from what I’ve learned from all of the knowledge here and other reading materials they are wrong....but back to my question.. would I be correct to assume, I need to pull the bronze elbows and copper pick up line out of my tank and replace with aluminium elbows with an aluminium pick up line or possible marelon? And once I do this the fuel line from the elbow to the racor (which looks simmiliar to a hydraulic line ) has a (carbon?) steel end fitting will still be better then what’s there presently?and would I be correct to assume the 1/4 ss screws I ised in the acess ports are a nessary evil and will be not perrrrrrrfect but ok for many yrs? Here’s some pictures of the ports and a picture showing a vent on another tank. Whhich is how my tank tap and pick up is.the elbow being bronze and the tube being copper.

[Eastward ho 24]

The plates and the fun stuff inside the tank; and forgot to mention I tried to clean the tank with seafoam first but slto no avail. Got acetone on a rag and that made it a matter of wiping off the sides and scooping out the sludge with a cup.

[a64pilot]

Copper can indeed be a serious problem in an aluminum fuel tank.
West Marine sells dip tubes that the elbow is aluminum and the tube a white plastic of some sort, cut the plastic tube to length of course.

[Eastward ho 24]

Didn’t see that on thier sit is that the name I should search it under?

[a64pilot]

No idea, I bought some at the West Marine store in Panama City Fl a couple of years ago.

[a64pilot]

Search on their site for fuel tank dip tube came up with this.
There is one with a longer tube too ,but didn’t see it.
https://www.westmarine.com/buy/moell...high--14970677

[boden36]

Inner tube rubber is not a good gasket material with diesel. Maybe better with some neoprene.


Regards,
Richard.

[billknny]

Copper and Aluminum? Bronze and Aluminum?

That is an easy one... no, NO, and NOOOOOO! Just do NOT do it.

Even a trace of salt water will dissolve the Al. I have seen a copper penny dropped on top of an Aluminum tank dissolve its way right down into the tank, leaving a hole behind, in months, not years. You can find pictures in corrosion texts of the same problem.

If you use stainless, be VERY sure you have all the connection points well insulated (PROPER gaskets, (no inner tube crap) Tef-Gel on screws, etc) and you can get away with it. Best not to do on top or bottom of a tank where water can pool, vertical sides are better.

Do this RIGHT or you will be ripping the tank out after it saturates the bilge with spilled diesel.

[out42]

Aluminium isn't much used as a fuel tank material nowadays as it doesn't cope well with sulphur in diesel, however apparently low sulphur the diesel is supposed to be. I know it's a pain, but while you're doing major surgery on this tank, should it be replaced with an SS one?

[Scout 30]

Originally Posted by out42

Aluminium isn't much used as a fuel tank material nowadays as it doesn't cope well with sulphur in diesel, however apparently low sulphur the diesel is supposed to be. I know it's a pain, but while you're doing major surgery on this tank, should it be replaced with an SS one?

Wrong. Aluminum is by far the most common fuel tank material. I just replaced my 30 year old aluminum tanks with new aluminum tanks.

[Rough Magic]

If this is a mission critical tank, then I think I might be tempted to put a fuel bladder inside and not worry about metals, old tanks, and corrosion.

If there is any pitting or poor welds that are visible,I would replace the tank or put in a fuel cell. They can be custom made to fit. Easier than ripping the boat apart.

[a64pilot]

Originally Posted by Scout 30

Wrong. Aluminum is by far the most common fuel tank material. I just replaced my 30 year old aluminum tanks with new aluminum tanks.

Why did you replace them? Why not plastic?

[out42]

Originally Posted by Scout 30

Wrong. Aluminum is by far the most common fuel tank material. I just replaced my 30 year old aluminum tanks with new aluminum tanks.

Well I'm happy for you! Common doesn't = best and all but one of my 10 boats have used anything other than aluminium. The one with aluminium sprang a leak at a seam which had corroded, a messy event and replacement with SS.

As someone else pointed out, why run that risk now?

[a64pilot]

From my understanding SS fuel tanks don’t last any longer than aluminum, or Iron.
Monel or Titanium May be the only real long lived metals for small Boat tanks, both not cheap, so why not plastic? As long as they are kept away from UV, which they would be, the life ought to be nearly infinite?

[Eastward ho 24]

Yes my tanks are in good shape, and ripping them out I'd have to rip out most of the structure cabinetry etc. That's not an option...I was thinking bladders but I've heard they don't hold up well as aluminum.. I've ordered some aluminium 3/8 elbows to replace the bronze ones and I'll Tig weld an aluminium pick up tube in place. I should thinking about that tuff gel stuff and in my opinion it's just snake oil. If the threads are engaged your gonna have metal to metal the snake oil will just squeeze out.