PS Advisor: Can Water Tanks Be Used for Fuel?

Maybe, but there are several factors to consider.

We made the embarrassing mistake of putting fuel in one of our water tanks (built-in fiberglass tanks). The silver lining is that we were trying to figure out how to expand our fuel capacity. Can you advise me on how to figure out if the tank can serve as our new fuel tank?

Phil North
Via e-mail

There are very specific specs for fuel tanks on boats. If it’s a current model, contact the maker. If not, you should be sure it meets American Boat and Yacht Council standards for fuel storage. For more on these standards, check out "Diesel Fuel Tank Replacement" in the May 2007 issue.

Diesel fuel in a fiberglass tank may work if the tank was molded with a diesel-resistant gelcoat or epoxy barrier coat. While water tanks require a potable water coating, diesel fuel is far more chemically aggressive than water. Another concern would be whether the design actually uses the inner skin of a cored hull as one side of the tank. While this could work, we wouldn’t recommend putting fuel in such a tank as liquid may find its way through voids in the FRP and into the core. That is bad news if it’s water, but it would be disastrous if it were diesel. And then there’s the issue of the bottom feed on a tank made to hold water and the no-bottom-penetrations regulation in fuel tanks standards.

The long story short: There are some big issues to consider that may rule out the transition.

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