Radiator leak

[Aleksander Mierzwa <alex@matrix.pl>]

Hi List,

I see the subject of cooling system problems is being discussed extensively
on the List recently, so I thought I could ask for advice as well :-)
About three years ago I replaced the radiator in my 5KT with all-metal one.
I didn't have much time nor experience, so I bought the first one I found,
manufactured by Danish company "Nissens". It was leaking since new. The
leak was from the solder joints were core meets the tanks. I added a "stop
leak" product to the coolant and this cured the problem. However, after I
changed the coolant some time later the radiator started to leak again. I
removed it and took it to the radiator shop. They resoldered the tanks to
the core, tested it and said it will be OK now. Several month later, the
radiator is leaking again in the same manner. So, my questions are:
1) Is it possible that the radiator is made of improper material that can't
be soldered reliably?
2) Could these problems be caused by improper coolant? I use a local brand
antifreeze labeled "ecological" (which probably means it's phosphate-free)
and "safe for aluminium". It hasn't caused me any other problems.
3) How often one can add the "stop leak" product to the coolant? Is it safe
to add it every time I change the coolant or am I risking clogging some
coolant passages?

On an unrelated note, I was having some Internet connection problems
recently, so sorry if someone tried to contact me and didn't get the answer.
Happy New Year everyone.

Aleksander Mierzwa
Warsaw, Poland
mailto:alex@matrix.pl
87 Audi 5000CS turbo (mine)
88 Renault Medallion wagon (mom's)
91 mountain bike (just in case both cars broke at the same time :-)