well,
i just saw this post & figured i'd throw in my 2 cents. i've worked in welding fab shops for over 20 yrs. & have many certifications, mostly with mig but some tig & stick too.
1st of all forget the flux cored wire it is not suitable for automotive use. all of the slag doesn't "boil" up out of the weld so you have alot of slag entrapment & the weld is brittle & prone to cracking on something that flexes like a car body or chassis. 75% argon 25% co2 with er70s-6 wire (most common for mild steel) is best. you can also weld stainless with this gas but you'll have alot of splatter. your gas supplier can rent you something more suitable for stainless on a temporary basis. straight argon is used for aluminum.
good service will be had from all 3 of the big names ( lincoln, miller, hobart ). i have a 175 amp lincoln & love it. miller & hobart are owned by the same parent co. "illinois tool works". miller is probably the best quality of the 3 having fewer plastic parts, but with the useage most home units will get, lincoln & hobart will be fine. go ahead & save your money & get a 230 volt unit. it will do anything the 120 volt welder will do & more. if you don't you'll wish you had. this is my most often ignored advice LOL!
the advice already given on aluminum has been good for the most part. it's best done with a spool gun do to the wire being soft. although i haven't tried it with my small wire machine, it may work ok do to the short lead. wire welding aluminum can be done well but it takes practice & won't work too well without preheating at least the 1st couple inches of where you want to weld with a torch. you'll see what i mean by running a bead on a piece of scrap aluminum with no preheat. for a ways the bead will pile up high & not penetrate deeply & then as the metal absorbs the heat the weld will flatten out & penetrate deeper & maybe even burn through depending on how hot you are running your machine. you just have to play with it & like i said practice.
as far as overhead welding goes, its no different than horizontal flat you're just uside down!! seriously it is this mind set that helped me learn welding over head. just imagine that you're not upside down & you're looking "down" on your work & welding in the horizontal flat position. oh yeah one more thing, try to position your body so you don't set your clothes on fire!
hope this helps,
robert.
