Actually, you don't want to use acid core, it will eat the radiator. Use a
tin-lead compound and a soldering paste with a flux brush. Also a caution.
The radiator is old, and it's very very common to "chase" leaks once you
apply heat to an old radiator. You may be tempted to use JB weld, but it's
not a good idea, neither is "stop leak".

Pull the rad from the car, wash it (inside and out) and drain it completely.
Set it down so that the petcock is pointing up and place a very wet rag
along the solder joint between the lower tank and the core. Use a propane
torch to heat and remove the petcock, holding the petcock with needle-nose
pliers.

Now it's time to clean. put the torch flame on the lower tank where the
petcock was. As soon as the existing solder melts, scrub the area hard with
a wire brush. Keep doing this until there's no contaminates left. Heat it
again, dip your flux brush into the paste and while the solder's melted
again, "scrub" the area with the solder paste and brush. You're trying to
get the area cleaned and tinned, with no actual dimension to the thickness
of the solder. Once done, do the same thing with the petcock. It's sometimes
useful to "feed" new solder to the surfaces and brush it away again with the
flux brush. This "replaces" the old solder and tins the area with the same
material you're going to use to make the actual joint.

Place the petcock back into the hole, and apply heat to the joint (aim for
the "thick" part of the petcock). as soon as the solder "flashes" (it will
turn from a dull grey to a silver grey the instant it melts), add a teeny
bit more solder from your coil and let the area cool. All the time you're
doing this, make absolutely sure that the seam between the tank and core
stays stone cold. Once done, cool the petcock with the wet rag and examine
the new solder joint carefully. What you're after is a clean solder joint
with a small fillet of solder between the petcock and tank. Paint it with
some black paint and you should be good to go. If you have the capability of
pressurizing the rad, you may want to do that but.......if the solder on the
petcock is weak enough to "go", the rest may not be far behind. Pressure
testing the rad may actually lead to more problems.  Go buy yourself a 6
pound cap and cross your fingers.

Good luck
Rob   Nov 2002  "Rob Stokes" <randc@imajis.com>
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