Now in my case I was forced to tear down the radiator. The thing held water and was in great shape externally and not rotten. But it was totally plugged with crap. So... here is what I did.
You need a proper Oxy-Acet torch. Select the smallest brazing tip you own, I forget what size it is, but it's the smallest one I own LoL
Now with the radiator well supported, heat along the top tanks seam where it meets the core. Heat about 2-3 Inches and then as the old solder starts to flow out grab your air line with a blow gun and very carefully "poof" the solder out. Continue this process until you have gone complexly around the tank...and with a little wiggling with a Welding glove protecting yr hand, remove the tank.
Do the exact same with the bottom tank.
Ok now you have the "core" Time to get it clean. I use a large plastic laundry sink fill it with a "hot" mix of oxalic acid and soak for 30 minutes or so... flush with a strong garden hose stream, and soak again until clean as you feel it may get.
Then I use a old dip stick from something. (had it for many years) The dip stick has been "roughened" a little with 36 grit. And I rod out the core with this carefully. I usually rod it once....soak some more rod again. While you are running your dip stick through the core keep a medium strong stream from your garden hose flushing the tube as you work. When I am sure it's flowing clean, I soak the core 15 more minutes.
I then remove it from the solution and I rinse heavily. I then immerse it in a mixture of simple baking soda and water for 20 minutes to neutralize the acid. Then rinse and dry....
At this point your tanks were also soaking right? Do the same routine with these minus the rod and your ready almost to reassemble.
Clean Clean Clean is the trick here. I clean all solder joint areas with a brass wire brush on a die grinder. Metal wire brushes can be used but I'd advise a re-dip in the acid to remove "reside" after use.
Once it's clean grab a clean brush, flux your joints heavily and with a low heat begin to heat slowly and start the process of fluxing a few inches at a time tell the black "goo" if ya will runs away from the joint. Do this all around your tank using as little heat as possible. When you have that done, begin soldering your tank back on.
The actual soldering takes a little practice but keep the heat low feather yr heat out along the seam and work slowly.You will get the hang of it. I use Tin Solder (50/50) and have never had an issue.
When done and cooled down I pressure test to about 5psi and reinstall. Always use distilled water/anti freeze to fill your cooling system.
So with some luck you have now just fixed a copper/brass radiator at home for almost nothing.
I will add some pictures of the finished project, and the next one I fix I will snap pics of the entire process for you....
