The "Ghost Line" is from the stuff used OVER the weld to finish it...period. If it were the metal expanding/contracting at the weld, every time the temperature changed, it would work harden and then crack...
No it wont. Ever seen a oil can situation from a hail dent? you can pop it back and forth all day every day and never crack the metal. Steel will flex a lot before it cracks from fatigue. If the difference in expansion is only .010" across the whole panel it'll be a difference that shows up at the seam, if the seam is hard enough to not flex with the rest of the panel. If you don't believe weld up a couple of pieces of scrap sheet metal, grind smooth, and bend it back and forth 2 degrees (that's more than enough to show through paint and more than you would ever get a panel to bend under heat expansion) and tell me how long it takes the metal to crack.
All I know is that all my welded seams are hammered down below a straight edge so I can get about 1/16" to 1/8" of all-metal coating on them. Sounds like perfection metal finishing may have backfired in this case.
Did you use a spot putty? If so what kind? Spot putty seemed to be the weak spot in the chemical cocktail that is new automotive finishes.
well, now i have a question after reading all this. My car is painted black and yes i have a ghost line on the top(chop). If i were to change the color on the top would the ghost line hide easier?
This thread is old, but I just read through it and saw that it was an '09 Malibu quarter replacement. You need to grind the two mating points so they have an angle to them instead of a sharp high edge. When the new quarter panel 'settled in' the top of it in the sail panel moved out a little bit... if you taper it and then use a bit of all metal or duraglass type filler that line won't come through. We were taught this in school for collision repair.
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