Big Al wrote:
"dpb" wrote in message
....
... use one that indicates it is a tannic acid (rather than
phosphoric acid).


Phosphoric acid?? That's used in rust removers like Naval Jelly, right? That
would eat up the rest of the cooler
....

I didn't say _use_ phosphoric acid, I said some rust converters contain
phosphoric acid as an ingredient. The phosphoric acid reacts with iron
and rust (iron oxide) to form a phosphate coating--a corrosion
retarder. In my experience, they're not as effective as the tannic
acid formulations in which the tannic acid reacts with the iron oxide
to convert it to iron tannate (with the blue/black-looking end result).

I don't recall a particular one at the moment but I did run into a case
a number of years ago where a converter didn't last long after use and
did some digging into it. The above is what I found then.

HTH...