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Old 29-09-2011, 07:49   #1
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Convert Plastic Water Tank to Diesel

Sorry I know this has been discussed before with stainless steal tanks or fiberglass but are there any material issues if I was to convert a plastic water tank to a diesel? Are there different grades of plastic tank?

On my boat (Beneteau Oceanis 46) all the tanks are plastic. Only difference I can see is the diesel tank is black and the water tanks are blue.
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Old 29-09-2011, 07:55   #2
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Re: Convert plastic water tank to diesel

Plastic is colorblind. You can put diesel into any polyethylene tank. Just make sure your galley pump is no longer plumbed into it....
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Old 29-09-2011, 11:39   #3
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Re: Convert plastic water tank to diesel

Nope...won't work.

There's more than one type of polyethylene. Water and waste tanks are made of low density LINEAR PE, which petroleum will permeate in a heartbeat, even "melt" the plastic.

Plastic fuel tanks are made of high density CROSS LINKED PE, which is impervious to petroleum. They're also supposed to meet some other criteria for USCG certification...a minimum wall thickness, all fittings on top, no surface that can allow liquids to pool etc. but that may only apply to tank mfrs, not to individual owner one-offs.

I should add that some of the early waste tanks were cross linked PE...I had one on my '79 Trojan. So you might find one that could be converted, but the odds are slim.
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Old 29-09-2011, 12:25   #4
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Re: Convert plastic water tank to diesel

Quote:
Originally Posted by peghall View Post
... Plastic fuel tanks are made of high density CROSS LINKED PE, which is impervious to petroleum. They're also supposed to meet some other criteria for USCG certification...a minimum wall thickness, all fittings on top, no surface that can allow liquids to pool etc. but that may only apply to tank mfrs, not to individual owner one-offs ...
Nonetheless good/best practice ought to apply to us, all.

ABYC Standard H-33, Diesel Fuel Systems, is silent on the issue of location of diesel fuel tank openings and therefore does not prohibit openings below the top of the tank.

XPE (cross-linked polyethylene) tanks undergo what's known as hydrocarbon expansion, which causes them to grow between 3 and 5 percent upon their first exposure to fuel. While this is a onetime event, it must be taken into account (a 45-inch-long tank could grow to 47 inches). Cribs, cleats, straps, and other tank supports must be adjustable to accommodate this expansion.
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Old 29-09-2011, 15:37   #5
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Re: Convert plastic water tank to diesel

ABYC Standard H-33, Diesel Fuel Systems, is silent on the issue of location of diesel fuel tank openings and therefore does not prohibit openings below the top of the tank.

ABYC standards aren't USCG regs. ABYC doesn't always restate regs in their standards for a couple of reasons: 1. compliance with ABYC standards is voluntary...compliance with CG and other federal regs mandatory. 2. the more times something is restated in new language, the greater the likelihood of error or confusion.

That said, it's also possible that there are different regs and/or standards for gas (petrol) than for diesel...I haven't kept up with that because I have enough to do just keeping up with the ones that apply to potties and plumbing.
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Old 29-09-2011, 15:40   #6
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Re: Convert plastic water tank to diesel

A buddy converted one of his his blue roto-molded water tanks on a Beneteau 393 to diesel. A few years now and he's had no problems.
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