Hello I would like to paint or coat my rusty exhaust manifolds . Has anyone tried some of the stuff in spray cans available at the parts store thanks in advance 

You can use chemicals like Naval Jelly to remove rust.  It's messy.  I have them bead blasted then paint them with Eastwood's High Temp Coating.  It has the look of cast iron. A little goes a long way.  As you can see, I have had this can for years.  It's nice because you can touch them up later.