Is it partially magnetic or not at all?  It's likely 304 stainless,
 but that would mean it's an aftermarket Y.. where did you get it? If
 it's stock, it's likely 409, but it should be partically magnetic..
 not as much as the mild you have, but dending on how weak the magnetic
 ficture is it might feel like it isn't drawing... those things are
 usually pretty sad as far as magnets go. I like keeping a bunch of
 neodynium magnets around, a pez sized magnet can have a couple pounds
 of pull all by itself, but DON'T get it hot or all that changes, and
 you have an expensive pez shaped lump of nothing exciting or useful.

 Welding stainless with a small MIG is a big PITA... you usually end up
 with lousy penetration, and lot's of frustration. And yeah just like
 any other kind of welding, the filler alloy makes a big difference.
 When joining mild to 304 I like to use 308 or 309, I've had good
 results with either, but lean towards the 309 now for no particular
 reason. For really high temp critical areas that simply can't be given
 the benefit of the doubt(like the turbo manifolds) I'll use 316 or 321
 stainless for the manifold, and 347 for filler to avoid carbide
 precipitation, conversion,  and stress corrosion cracking. Simply put,
 the lower carbon and higher nickel content alloys resist conversion of
 their grain structure in the heat affected zones of the welds better
 than higher carbon lower nickel alloys. Conversion to the less
 corrosion resistant, brittle, and magnetic martensite grain structure
 is pretty much like work hardening... the structure gets all messed up
 by actually growing/smearing in one direction and has lots of
 imperfections.. and you loose all the goodness of the austenitic
 stainless steel, that's why typically you join even 304 to 304 with a
 308 or 308L.  That's ALSO why if you're trying to machine or drill
 stainless, you'd better have loads of pressure and really slow slow
 slow surface speeds or you'll build up heat, convert the steel.. and
 then you're all done, will have half a hole with uber hard steel at
 the bottom, and a wasted blue and purple bit with melted edges. What
 were we talking about again?

  Jim Akiba

 On Tue, Apr 1, 2008 at 11:52 PM, neil N <musomuso@gmail.com> wrote:
 > Thanks Larry.
 >
 >  I ended up making my own "Y". I just wasn't sure about the metal type
 >  of the Jetta "Y", thus was unsure my welds would be good.
 >
 >  And as for flanges, I used a local fabricator/welder to weld the pipes
 >  to flange that mounts to exhaust manifold.
 >
 >  I didn't know there was a wire for joining SS an steel. Good to
know. Thanks.
 >
 >  Neil.
 >
 >
 >
 >  On Tue, Apr 1, 2008 at 8:37 PM, Larry Alofs <lalofs@gmail.com> wrote:
 >  > I ran into something very similar when I built the exhaust for my subie
 >  > conversion.  I wanted to re-use the flanges and Y 's and discovered that I
 >  > could not cut the pipe with a torch.
 >  >   If you are going to weld it with your MIG, you should look for a wire
 >  > alloy that is recommended for joining stainless to ordinary steel.  You
 >  > should also check whether you need to use a different shielding gas.
 >  >    I ended up welding mine with oxy-acetylene and had a lot of
trouble with
 >  > cracking.  Now I have found a flux that would have helped perhaps.  Very
 >  > educational; still more to learn...
 >  >
 >  > Larry A.
 >  >
 >  >
 >  >
 >  >
 >  >  On Tue, Apr 1, 2008 at 5:05 PM, neil N <musomuso@gmail.com> wrote:
 >  > > Hi all.
 >  > >
 >  > > Well, am somewhat embarrassed to say that I didn't check to see what
 >  > > kind of metal I was playing with. I was just about to tack it in place
 >  > > when I noticed it wasn't attracted to the magnet I use for holding the
 >  > > work.
 >  > >
 >  > > Here's some pics of part. Its' the "Y" I cut from the Jetta downpipe:
 >  > >
 >  > > http://tubaneil.googlepages.com/temp%22y%22pics
 >  > >
 >  > > There appears to be corrosion inside, but maybe not the pipe reacting.
 >  > >
 >  > > It is not attracted to my magnet. (how I found out)
 >  > >
 >  > > It feels too heavy to be aluminum and doesn't grind/file like it either.
 >  > >
 >  > > SS?
 >  > >
 >  > > --
 >  > > Neil Nicholson. 1981 Air Cooled Westfalia - "Jaco"
 >  > >
 >  > > http://web.mac.com/tubaneil
 >  > > http://tubaneil.googlepages.com/
 >  > >
 >  >
 >  >
 >
 >
 >
 >  --
 >  Neil Nicholson. 1981 Air Cooled Westfalia - "Jaco"
 >
 >  http://web.mac.com/tubaneil
 >  http://tubaneil.googlepages.com/
 >