On Mon, 11 Jul 2011 15:11:56 -0700 (PDT), wrote:

On Jul 11, 3:57Â*pm, Ignoramus24437 ignoramus24...@NOSPAM.
24437.invalid wrote:
I have a 22 gallon (or so) fuel tank that originally had gasoline in
it.

I want to use it for diesel.

I would like to drill it and install a through-hull fitting, which
would be for the fuel return line. Ideally, I would like to braze the
fitting in place also.

My question is how do I drill it and braze, so that it would not
explode.

The tank has not had gasoline in it for a couple of weeks.

Today, I recently set it up with the fuel cap open, turned it over so
that the fuel fill hole pionts down, and set it out so that it would
becmoe quite hot under the sun.

Would it be correct to assume that after a few days I could purge it
with compressed air, and then drill and braze it, without exploding?

Would purging with argon be a good idea?

i

Steam clean, if possible. Just a little vapor can cause a lot of
trouble. Old-timers would work on one if it was filled with water
first. Inert gas is a good idea, but how can you tell if it's full
enough? With water, there's no doubt.

Stan
Filling an old tank with water is NO guarantee you will not have a
problem - and if you do, all the water is forced out the filler at
once, under high pressure. Had a friend tried welding the tank for his
53? ford that way - and he caught the tank in the chest as it emptied
itself, forcefully, against the shop wall where he had it stood up. He
ended up flat on his back on the driveway - quite sore. Not sure if it
was just steam, or if some gasoline vapour managed to ignite - but it
appeared to be significantly more powerfull than you would expect of
steam, given the amount of heat involved and the short time the torch
had been applied. He was just trying to solder or braze a pinholed
area (rusted) on the end of the tank, which was pointed up.

You can't get the tank hot enough to solder or braze when it is
TOTALLY full of water, so there had to be enough "air space" to either
trap steam or gasoline vapour.

I'm betting on gasoline trapped in the rust scale at the weak spot in
the tank.

I know a lot of old mechanics who would run exhaust through a tank for
half an hour before attempting to solder, braze, or weld on it.,

With inert gas fill, you can weld at the BOTTOM of the tank, where you
KNOW it is full of (particularly) CO2. Plug the hole as much as
possible to keep all the CO2 from draining out before you finish the
job.

I've repaired oil pans while still on the engine using this method -
any other method is foolhardy (on oil pans)