How do u get rust off a car

The long lasting way is to cut out the rusty metal and replace it with new. The not so long lasting way is to sand/grind off the rust. Fill with bondo and paint. Rust will return in two to three years.

Unless the rust is only minor surface rust. Then one can sand it out of the metal and epoxy primer will do a good job of preventing it from getting worse. Like tenspeed said though, if the rust is deeply pitted into the metal or if it is a rust hole, it needs to be cut out with fresh steel welded in its place

Muriatic acid under a control environment maybe 10 to 15 % or Pro 15 covers it will not come back

Media or soda blasting will clean everything off and show you exactly what needs attention. You can do this yourself, but be very careful, as heat can build up and warp panels. Once everything is exposed, you can decide what the best course of action is. I have been known to use a Dremel tool to clean small areas completely, then use a rust inhibiting primer such as is offered by "Rust Checks". Then spot putty and more primer. Done right the rust did not return even after 20 years. My other trick is to outline the trim with pencil, then carefully remove it. Sand lightly, fixing any rust that has started, and coat the area with rubber spray on stone guard, paint, and replace the trim. Since the stone guard is covered by the trim, nobody knows it is there, but it prevents galvanic reactions between dissimilar metals, which is the main cause of rust under the trim.