I've decided to continue with the GPA radiator restoration.
As shown here above, it's rather easy to detect where there are tiny holes in tubes or missing solder around the tubes.
After cleaning with NaOH, I've detected no less that 25-30 holes, all in the upper part of the radiator near the header.
Most of them are missing solder, but a few are holes in the tubes.
I believe that the holes are all concentrated in the upper part, because that is near the coolant surface in the radiator.
Old coolant becomes more corrosive and the oxygen near the surface makes the rest.
That radiator was treated with Stop Leak that can be found in the tubes.
That product is quite effective.
It was removed when I've treated the header in the caustic soda- NaOH bath to remove the paint and other foreign matters.
Now it's time to repair the holes with tin solder ... and solder wick.
Before soldering with tin, the header and the top of the tubes oxidation have to be stripped with HCl / muriatic acid.
Same process as the one described by Lew in another thread.
The goal is to prepare the header and the top part of the tubes to be soldered.
The top part of the radiator soaking in HCl.
Then it will be cleaned up with clear water and dried up.
Now I need to re-create the solder joints where they are missing or leaky.
I've first applied liquid flux on the header, total surface.
Here is a picture of the soldering process.
I've used a torch with a large tip for the first general tin wetting and a fine tip for the specific tubes repair.
The header is always heated up from the bottom side on the images.
The tin solder has never to be touch by the flame. The solder melts against the metal when the metal is hot enough
A good solder can be seen via the capillary effect like this. The solder goes up and "wet" the tubes:
The process is easy and quite fast : you progress slowly from the left edge to the right edge while adding solder on the top of the header.
The you wait until the night, and in the darkness you check again the leaks with the flashlight.
There were still many holes above the solder joints, in the tubes.
It's difficult to fill up a hole with tin solder, because the tin solder is sucked at the bottom in the solder bath when you heat up the header.
So I've used a little trick : solder wick.
Solder wick used in electronics ... and yesss, it's Made in USA
I cut what's necessary to surround the radiator tubes and I apply that piece of wick directly against the tube.
Then I add the tin solder which will be sucked by the wick which in turn will be solder to the tube.
I've used tin solder wire with resin in the core.
That wick patched a large hole. Yessss!
And the tube is still free form solder in the inside.
Easy to solder, not so easy to place the wick around the inside tubes.
There are 4 rows in a GPA radiator.
By the end of the restoration, the header will be soaked in baking soda to neutralize the acid and flux residues from the soldering process.
Then it will be time to re-solder the tank and pressurize test the radiator.