I have a steel tank that leaves a bit of rust in the filter.

------------------------------------------------

Dear Doug,

Rusy in your filters is good evidence it's time to clean & slosh the fuel tank.
The hazard here is two-fold; the most obvious is that your tank is generating
a contaminant that can lead to an engine stoppage. But the less obvious
problem is actually the more serious: Your fuel tank is dissolving. It will
eventually begin to leak.

-------------------------------------------------


Will sloshing
the tank solve the rust problem?

-------------------------------------------

No. In fact, it could make things worse. Sloshing will encapsulate the rust
but won't stop it. But when you apply selant over rust, even the
self-neutralizing crap -- PQR or whatever -- there's no guarantee the rust
won't flake or spall. That destroys the sealant and usually gives you some
industrial-grade contaminants to deal with.
You need to deal with the rust first, then seal the metal with a sloshing
compound that is impervious to gasoline.

------------------------------------------------

If so, what compound do you recommend for
steel and should it be etched with anything beforehand?

D.
--------------------------------------------------

Compared to some of the more expensive polysulfide-based sealants, I've had
better results from PVA. This is on tanks I've made myself out of steel (for
vehicles) and aluminum, both riveted and welded, and from fiberglas. I ended
up with leak-free tanks and taught me how little I know about tanks, in that
there are myriad details specific to each type of tankage that must be
addressed. For that reason I'm reluctant to make a recommendation for
something that would be applied to another person's work. Not saying mine is
better but that it's impossible to know the details of the construction.

No matter what you use as your sealant, its durability is largely a function of
prepping the surface. With a steel tank you need to get rid of all rust,
repair any leaks then neutralize whatever acid you've used to get rid of the
rust, then get rid of the neutralizer and then dry the tank. A haze of rust
will form on any steel tank as soon as it's etched & dried but it doesn't
appear to affect the bonding of the sealant nor its durability.

Sulphuric acid is less expensive than phosphoric but it's chemical composition
appears to promote faster rusting than does phosphoric. (I'm talking minutes
here, as in the time between one step and the next.)

If if you've no experience with tankage or radiatiors you'd best stick with
phosphoric. In fact, if you've never done this sort of thing before I would
probably be best to start with something like a rusty oil drum. Or even
de-rusting some metal coupons using acid. Or best of all, having someone else
do the work. Radiator shops are your best bet but there's lots of welding
shops that specialize in tankage. They know all about acid etching,
neutralizing and sealing.

Since you're flying with an iron fuel tank I'll assume it's fairly small,
possibly in a T2 or similar airframe, in which case the wisest option may be to
simply frabricate a new tank, except this time out of riveted aluminum rather
than riveted & soldered galvanized sheet.

-R.S.Hoover