Diesel tank corroded through

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PCUK

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Just took the ali' tank out to fit an inspection hatch and after cleaning and degreasing noticed water on the floor beneath the tank. Tiny corrosion holes all over the bottom. Thought the fuel leaks were from the engine but apparently not. Fuel from the tank had entered the engine compartment under the rotten engine compartment bulkhead rather than the other way round. Ordering stainless sheets this week to make the new tank. What's the normal thickness used for small diesel tanks (about 70 gallons)?
 
Remember to put enough baffles in the tank to stop the sides flexing. Stainless tanks can crack down the welds on the corners if the sides flex in and out too much.
 
Stainless steel is not a very good material for fuel tanks in boats.

unless you have a narrow boat used on calm water the bumps and stresses your tank endures will fracture the stainless steel weld.
Stainless is too ridged for this application.

Even if you dont go out in F5-6 pounding the waves @ 20 knots the first time you road transport the tank will rupture.

I have had the exact same pin prick holes in an aluminium tank ( Bayliner 2651).

I went through 4-5 tanks before I eventually had one imported from usa , I should have had a patch welded to the bottom of the tank and refitted the old one, the pin holes are most likely, where bilge water had caused an electrical current, the holes are almost certainly restricted to the base only, the rest of the tank will be good. I would explore the idea of an aluminium bottom welded on the current base.
 
Suggest you get a plastic tank - hopefully you can use a standard shaped tank from Vetus or Tek Tanks, either of which will be cheaper and better than an SS one. If you have to go the custom route, plastic is usually competitive with SS.
 
Thanks for all the info'. Signs of corrosion all over the ali' tank so it's scrap. I thought tig welds on stainless were less prone to cracking. I think I'll go for mild steel. Last boat had one for 30 years and no problems with that.
 
There is an alternative which we used to good effect, it's called Tank Re-nu, basicaly involves coating the existing tank inside and out with rubber, they do this for obsolete vehicle tanks for classic cars etc, it is a simple process of sending your tank via courier and geting it back by return a couple of days later, cost is a fraction of a new tank.

http://www.fueltanks.co.uk/pages/renu.html
 
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Go for a replacement pukka metal tank.

How long did the last aluminium tank last?

Aluminium is used because its easier to use, stainless welds are more brittle and prone to fracture or pull through, dont go for very thin gauge stainless.

Take advice as to quality of aluminium.

Probably you had water in the tank and a bit of diesel bug aparently the bi products from the bug is very acidic an attacks aluminium, the worst I have seen is in a 3 year old british built motor cruiser it went right through the aluminium ! I would use a good quality Biocide for the bug such as Grotamar 82.
 
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