I have an angle grinder that i bought toclear the rust out of the floor. The book that came with it said you could get sanding and polishing discs for it, but i was afraid that it might gouge the outside of the car. Are there any discs that would be safe to use on the outside of my car? Its a 4 inch disc witha 5/8 in arbor.
any help is greatly appreciated.

The grinder you are describing sounds like it would spin way to fast for use on an exterior panel with a grinding disc. Speed causes heat, heat causes warpage. Unless it has a variable speed trigger enabling you to slow it down, most don't.

i was watching one of the car shows, i think it was trucks, they showed a disc they said didnt produce much heat so it wouldnt worp the metal but i didnt catch the brand or anything that would help me find out what it was.

A Grinder is VERY DANGEROUS to use on the body skins. IT IS RISKY ! Even experienced bodymen have to be EXTREMELY careful and we usually use a 7" grinder. You MUST start the grinder on the panel and pull it off before stopping it. If you don't you are cutting grooves/holes! You have to use a FAST criss cross pattern and a very gentle hand, NEVER pausing for a second.

I would suggest that a Dual Action or Random Orbital sander be used. You can get 40 grit and cut it to primer and then step up to 60 or even 80 grit when you start to see steel. It's slower but safer as a grinder will show no mercy.

If you have to use a grinder, then tape off the crowns and edges with duct tape, work the flatter areas and in the curves be extra gentle and keep the cut soft to the primer ONLY. Really try to keep from going through the primer with a grinder and use a DA to go through the primer. The only exception is if you are digging out rust and cutting for filler work.

It's better not to rush otherwise you might discover a new route to China or the cookie farm ;)

Hope it Helps.