Rust and Paint

Yes on the whole thing. If you don't paint the whole thing, the colors will not match up. If some of the existing paint is still very firmly adhering to the metal and doesn't want to come off with a wire brushing, it should be OK to paint over it after a good sanding/scuffing up.

It might be easier to brush or roll the paint than to spray it; that's somewhat of a personal preference. (Rustoleum and similar paints do roll pretty nicely with a foam roller, possibly with a touch of thinning. With a little bit of care it can give a nice smooth finish that compares very well with spraying.)

Google POR-15. It's another option.

I would prep and paint the whole thing, not just the rusted area.

Should I paint the whole bar or just the area with rust?

Yes, do a good wire brushing. I however would use Hammer-rite paint. It has worked well on my steps, tow bar brackets and trailer hitch.

Take a wire brush on a drill clean rust and paint until shiny silver metal is seen, spray paint with metal primer and then paint with black paint, when using a can do not try to paint all at once you need to do it in several passes, buy good paint and primer.

navegator