Engineering, not IT here.
Previous company, no dress code to speak of. It was in Texas and so far as I can tell the only rule was pants, shirt and some kind of footwear required unless you were in the lab. Sandals, flip flops, messed up shorts, tshirts with logos/text were all fine. I resisted on wearing shorts for a long time but eventually gave in as wearing pants in 100+ heat just sucks.
Current company, no formal dress code to speak of. But people dress better here mostly. Nice jeans, khakis or slacks. Polos, button down shirts or maybe plain t-shirts. I think I have only seen one person wearing a tshirt with something printed on it and that was my manager three levels removed. First summer here but I don't expect to see anyone in shorts. We also have customers come to the site but I don't think they ever come through engineering so that isn't a huge concern.
Even with a lax dress code no one came in smelling bad, just dressed way down. Dunno why IT would be different but maybe it is. IMO business casual is as formal as IT/engineering should have to be in any occasion, even customer facing.